Showing posts sorted by relevance for query century/21. Sort by date Show all posts
Showing posts sorted by relevance for query century/21. Sort by date Show all posts

Thursday, January 7, 2016

Oh what a relief it is...

Fixing the Ten-Tec Century/21 Sidetone

I get some strange enjoyment out of using my 1977 Ten-Tec Century/21 CW-only novice rig.  It is a primitive radio for QRP(ish) CW operations but it has a charm that keeps drawing me back.  Maybe I just like to take the road less traveled.

Foreground: Audio pre-amp board in the bottom half of the Ten-Tec Century/21

It has a charm but something had to change

If you've previously read my blog you'll recognize one of my nits about the Ten-Tec Century/21 concerned its sidetone.  The same quad op-amp LM3900 chip is used for both the audio filter and produce the buzzy, square-wave sidetone.  The side tone pitch is fixed at 475 Hz while the audio selectivity filtering is centered around 750 Hz .  The sidetone volume on the C21 is adjustable but the pitch is not.  The later model Ten-Tec Century/22 offered adjustable pitch for the sidetone.

I had learned to live with the obnoxious sidetone and somehow even appreciated its novelty until I built an Elecraft AF1  kit to tighten the audio-bandpass filtering for this radio.  The Elecraft AF1 does its job very well; so well in fact that when zero beating a CW signal it results in the audio peak pitched at 750 Hz (the natural center for the C21 audio filter), the external Elecraft audio filter in its tight filter mode then filters out the sidetone which is pitched a few hundred Hz below the CW audio signal.  That means that while my AF1 filtered the incoming CW wonderfully and provided much better selectivity than that provided by the C21's built-in filter, I couldn't hear my sidetone when sending.  I could hear the clacking of my straight key but when using a bug I was literally deaf to what I was sending. 

I got around this problem temporarily by using my HAM Keyer as my key interface to the radio and listening to the sidetone from its external speaker (keeping one side of my headphones ajar).  Well that quickly became bothersome; both to me for having to wear my headphones askew, and to family members within earshot of the external keyer's audio.  

The pitch of the sidetone needed to match the pitch of the received CW

So I decided I needed to change the pitch of the sidetone to match the 750 Hz audio center of the CW filtering built into the radio.  Doing so would allow my external bandpass audio filter to pass the sidetone at the same pitch I'm listening to received CW.

A kind ham (WA4FOB) sent an email suggesting that I modify the op-amp circuit generating the sidetone.  He told me that I needed to change the resistance of R1 in the 80356 audio preamp  schematic.  But apparently Ten-Tec made some running changes to the pre-amp audio board because quite a number of resistor values on my board didn't match the values listed in the schematic. For example, the schematic showed R1 as a 68K resistor but no such resistor with that value was on the board.  

A bit of detective work was required.. 

The 80356 preamp audio board is directly connected to the AF and Selectivity knobs on the face of the radio and removing the board turned out to be more difficult than it should be (longer story not recounted here).  So without the ability to trace the circuits from the bottom of the board I had to determine the correct resistor to modify by tracing it backward to the correct pin on LM3900 by measuring resistance between components.

Op-amp schematic for the TT-C21 sidetone

The result

In the end it took me a little over an hour to find the correct resistor and then, with some trial and error, determine the correct resistance to add in parallel to bring the pitch up to 750 Hz.

R1 on my radio turned out to be a 47K ohm resistor rather than the 68K value indicated in the schematic.  I knew that I needed to lower it's resistance to cause the tone generation to raise pitch so I tested a few resistor values before settling on a 33K ohm resistor to be used in parallel with R1.  That gave me a resulting resistance value of:

1 / (1/47000 + 1/33000) = 19387 ohm

A resistance of 19387 ohm results in the sidetone pitch generated by one of the LM3900 op-amps very near my goal of 750 Hz.  The sidetone pitch now lies within the bandbass of my external filter and matches the received CW natural volume peak at 750 Hz. Another benefit of raising the pitch  has been to smooth out the brassy square wave.  It is now quite pleasant to listen to.  I may miss that old buzz-saw sidetone...  Nah, I won't.

All-in-all this was a fun little bit of detective work for an electronics novice such as myself.  I am quite satisfied with the result of this simple modification.

33K ohm resistor soldered in parallel with R1 to raise the sidetone pitch to 750 Hz

Scared of electronics?

I must admit that even though HAM radio has historically had a strong focus on electronics my background is completely devoid of working with electronics.  I was simply an "appliance user" of radios. But purchasing this old, inexpensive radio has been a boon for learning about a subject I should have studied long ago.  When I bought this radio it had a number of quirks.  The radio arrived with previous owner(s) modifications for driving an external amplifier and other "features". Some of those modifications negatively impacted both the QSK and the drive adjustment.  I spent hours studying the schematic and probing around the radio before I determined what to remove to get it back to a more factory-standard state.  It has been a great learning opportunity.  Since the radio was relatively inexpensive I am not too concerned about breaking it and the circuitry doesn't get much simpler in a transceiver than this.

Pick up an old clunker to mess around with

My little investigations under the covers of this rig have encouraged me to consider building something more complicated than the regen-radio and audio filter kits that I've built to-date.  Without the Ten-Tec C21 I don't think I would have the confidence to move forward in my nascent journey into the world of electronics.

If you are an amateur radio operator who, like me, is a total novice at electronics consider picking up an older solid-state radio such as this one just to learn about electronics and experiment on.  I think it will encourage you to learn more and become a better ham.  
But as with all things that run on and generate voltages that can maim or kill, go slow in your learning process and take precautions to keep yourself and bystanders from injury.

That's all for now.

Lower your power and raise your expectations

Richard, N4PBQ

Wednesday, January 25, 2017

Hard fought SKCC QSO using the Ten-Tec Century/21

Sometimes you need to move your QSO

My ever changing station configuration
Left to right - Elecraft KX3, Ten-Tec Century/21 with Ten-Tec Eagle on top, the MFJ 493 keyer on the right
4 keys - Navy Flameproof, Kent Hand Key, Vibroplex Bug, N3ZN QRP paddle
The Elecraft AF1 audio filter is sitting unused in front of the Century/21
After starting our QSO the ARRL QST program started right on top of us causing QRM that forced us to move to another frequency
My old Ten-Tec Century/21 is a lot of fun to use and its direct conversion receiver makes CW sound beautiful. But the frequency dial is fairly imprecise so when I asked the station to QSY up 1kHz finding him again was a bit of a challenge.  When I heard him I had to zero-beat him again to make sure I was on the correct side of the direct conversion receivers passband.

Enjoy the QSO and the QRM dodging...

Shooting this video

This video was a bit harder to shoot than what I normally do.  I usually place my camera to one side but I wanted to use my fisheye lens and shoot the QSO from above.  

While shooting I was straddling the tripod with the camera right in front of my face so I was reaching around the tripod to use my keys and get to my keyboard for logging.  It was a bit awkward, and in the video you'll see me bump the VFO while trying to operate the radio because I couldn't really see what I was doing.  It's always fun to add a level of difficulty while making these videos.

That's all for now...

So lower your power and raise your expectations

Richard AA4OO

Friday, February 5, 2016

Making use of Elecraft Mini-module Kits

Connecting the bits and bobs

I have enjoyed building Elecraft Mini-Module kits.  Now to put them to use...

Elecraft Mini-Module Kits

What to do?

I built the kits as part of my learning adventure and to improve my soldering skills.  It's also helped me learn to follow instructions better (my wife says I need to work on learning to follow instructions).  But ultimately these modules are intended to be useful, and in my case they work nicely to when operating my old Ten-Tec Century/21.

My Ten Tec Century/21 is a 1970s CW-only, low(ish) power rig originally intended for Novice license holders of the time.  It has no RF output meter or SWR meter.  It has poor filtering/selectivity compared to modern radios and its analog tuning dial is a bit vague so you generally only know your frequency within 5 kHz. 

The mini-module kits prove useful. I employ the W1 Wattmeter to determine my power output and SWR; the CP1 directional coupler is used to send a 20db attenuated signal to a frequency counter to determine operating frequency, and the AF1 Audio Filter makes operating near adjacent CW signals more pleasant by providing a narrow audio-band-pass filter.  The result signal can be transmitted through a LDG tuner into the BL2 switchable balun connected to my attic Doublet.

Bring out your cables

All these independent modules need to be connected, so tying the bits and bobs together requires a few coax jumpers to route the RF around:
  1. UHF to BNC from the radio to the W1 Power meter
  2. BNC to BNC From the W1 Power meter to the CP1 coupler
  3. BNC to UHF From the CP1 coupler J1 input to switched T1 output to frequency counter
  4. BNC to UHF From the CP1 coupler J2 output to the tuner
And other cables:
  1. Serial cable from the W1 Power meter to the computer
  2. 12v power cables for the W1 and AF1 (unless I want to use 9V batteries)
  3. Audio cable from the TenTec C21 to the AF1
So it's definitely not a neat and tidy setup at present. I plan to arrange things more neatly and possibly place the W1, CP1 and frequency counter into a single box. But for now it's fine and I like the flexibility to switch things around or pull a module out to use somewhere else as the mood strikes.

AF1 Audio Filter making crowded band operations pleasurable
CP1 Directional Coupler sending off 20dB attenuated signal to the frequency counter

Frequency Counter fed by the CP1 directional coupler.

W1 Power Meter sending its measurement off to the computer

W1 Power Meter Output to Computer

The W1 has a serial output to a PC for use with the Elecraft W1 software.  The software can both configure the meter and display more detail than can be determined from the LEDs.   Source code is supplied and the command set is documented so it would be easy to write your own software for this.

The W1 power meter LEDs give you relatively discrete output information for the lower two ranges (0.1w to 1.4w) and (1.5w to 14w).  But in the high range (over 14w) the LEDs are only displaying 10 watt intervals.  For instance in the high range, when the second LED is lit you don't know if your operating just 20 watts or 29 watts.  It won't trip the next LED until it crosses the 10 watt boundary in the high range so it can be useful to look at the measurement on the computer if you are operating QRO.   I'm not complaining.  I understand that the meter is primarily intended as a QRP meter and for QRP power (less than 15 watts) it offers plenty of information.
Here I brought the TenTec Century/21 up to nearly full input drive (55-60 watts) to see what it could output. The rig probably had a few more watts left in there but I didn't want to push it because I haven't gotten around to replacing some of the out of spec components in the internal power supply.  I normally use this radio under 10 watts (I look for about 30 watts input on the drive meter) but I was curious to see what the old girl could do since I had the meter hooked up to the computer display.
Measuring maximum RF output from the Ten Tec Century/21
The computer interface is a nice touch and the ability to modify the source code to suit is a plus.

Nits and Quibbles

My antenna's native SWR at 15m (~21.08MHz) is around 2.5 so it requires tuning (impedance matching).  After my LDG auto tuner spends a ridiculous amount of time trying to find a match it settles at 1.7 SWR according to the W1 Wattmeter, while the indication on the Autotuner is that it believes the SWR is 1.5 or better, while the radio on the other side of the W1 meter sees a SWR over 2.5.  I only see this behavior on 15m so I think there is some strange impedance reaction occurring in the W1 wattmeter that is changing the reactance on the jumper to the radio.  I've tried a few different jumpers, swapping jumpers, etc.  But it always presents an abnormally high SWR to the radio at 15m.  Now when I transmit into a dummy load I don't see this behavior, so it is some combination of SWR / reactance present at W1 that causes a impedance mismatch downstream toward the radio.  I have more investigating to do but for now I am choosing to not use the W1 Wattmeter in-line when operating on 15m.

The CP1 directional coupler is not entirely transparent and raises the SWR by a bit as signal passes through it.  You would expect there to be losses according to the -20 db taps (one forward and one reverse).  This should work out to about 0.08% loss but I wouldn't expect it to raise the SWR. It adds about 0.1 to your SWR  and occurs even if the forward and reverse couplers are switched "off" and shunt their respective loads to the on-board 50 ohm resistors.  I'm unsure what accounts for that slight SWR bump but be aware that CP1 contributes some very small losses.


So the Elecraft Mini-modules are fun to build; and with enough jumper cables, can be combined for experiments and general augmentation of other equipment in your shack.  So go out there, build some kits and experiment.  It's a rewarding experience.

I'm trying to decide what I'm going to build next.

That's all for now... 

So lower your power and raise your expectations


Richard, N4PBQ

Friday, October 23, 2015

TEN-TEC Century 21 --- Vintage Novice CW Rig

TEN-TEC Century 21

A second HF rig has somehow found its way into my home.

Ten-Tec Century / 21 CW Only Transceiver

Since getting back into HAM radio with my focus now on CW and QRP I find that many of my contacts use old and/or homebrew equipment.  Maybe it's because I often call CQ with my straight key rather than paddles that results in most answers to my CQ being operators using a straight key or a bug.   It seems these operators tend to not use the latest piece of shiny gear, which made me an anomaly; sending with a straight key while using my SDR-in-a-box like the Elecraft KX3.  Maybe for this reason I've found myself being drawn to less sophisticated types of equipment.  I'm not talking about wanting to go back to spark gap and gravity batteries, but sometimes the KX3 is just too easy to use.

In the same way that I'd prefer to send CW using a Straight Key to a keyboard since it's a greater challenge, I think that the older, less sophisticated equipment can bring more satisfaction to the hobby.

Vintage... like bell bottom jeans and corduroys 

Now don't get me wrong, I'm not suggesting that the only "real" radios are those with discreet components or tubes, nor am I saying no key but a straight key.  I'm just moving through some stages of the hobby that I missed because I didn't grow up with this older equipment and I think the challenges can be fun to learn and operate.  
I didn't get into Ham radio until 2006 and the commonly available used equipment of the time was microprocessor controlled rigs with digital displays, optical encoders, DSP filters and seemingly endless menus for configuration.  I went through a few HF radios over a couple of years: a Yaesu FT-857, ICOM 730 and lastly, a ICOM 746 Pro, before I sold the radios and dropped out of the hobby. At the time none of those rigs held any "magic" for me, they were just tools with increasing levels of functionality and ease of use.   However the ICOM 730 did hold copious amounts of stale cigarette smoke and nicotine from the previous operator that it would release into my room as it warmed up.  Not really magic, more of a non-corporeal element let's say.

If you've read my earlier posts you may recall that although I like my Elecraft KX3 immensely I have some strange fondness for TEN-TEC equipment.  Ten-Tec has made some quirky radios with legendary full break-in QSK and supposedly smooth, quiet receivers for CW operators for a few decades now.  So when a Craigslist posting leaped into my browser window (I don't know how that happened) advertising a seemingly pristine late-70s rig that had supposedly been reworked to a perfection, all for $140, I just couldn't pass it up... well at least the price in the ad was accurate.

The Ten-Tec Century 21 is an interesting transceiver.  In the simplest sense it was an ideal radio for the Novice Licensed HAM operator of the 1970s.  It is a CW only transmitter.  It doesn't require fiddling with a resonant tank circuit of the typical tube radios of the era to work out resonance.  It has a built-in power supply that runs off 115-120v mains.  It doesn't use a superheterodyne receiver but a direct conversion receiver (Ten-Tec called it a double direct conversion receiver).  This resulted in a simplified design and good selectivity but without the IF there is no AGC so be ready to work those RF/AF gain knobs.  It also has easy band changing and nice filtering.  From web searches and reviews its most common problem is a PTO that has to be rebuilt every few years.  The Ham I purchased mine from said it had been rebuilt.  It doesn't slip (yet) but it's kinda stiff so I expect a PTO rebuild to be in my future.  I spoke with a ham I work with who has rebuilt one and he said it's not difficult, simply time consuming (but he repairs electronics all day so YMMV).

Operation is relatively simple:  

  1. Start with the radio off.
  2. Turn the Drive knob down (counter clockwise), select your band 
  3. Turn the radio on by pushing in the RF Gain knob (it is the on-off switch).
  4. Find and open frequency (wait, listen, wait again, listen) and while holding the Set Drive button apply just enough power using the Drive knob to give you some RF out for matching your antenna.  Better yet use a frequency analyzer to tune QRM free.
  5. After you're matched up you can bring the power up to where you want to operate.  Unfortunately this can't necessarily be done into a dummy load unless you're match is near 1:1.  The SWR will affect how much output drive you can use.  If you're going to run QRP then no worries because you won't be running the power input up to a point that could trip the final, Maximum input power is marked by the thick line on the Input Power meter (about 70w).  This results in differing output wattage dependent on antenna resistance and frequency.  I found that into a 50ohm dummy load I could generate up to 40w output for 80m, 35w output for 40m, 30w output for 20m and so on, down to about 15w output on 10m.  As I plan to use the rig for QRP this is mostly academic.  It certainly can provide more than QRP output levels if conditions warrant.

To Tune a Station prior to the QSO

This seems more complicated than it should be but I'm guessing after I've done it a few dozen times it will become automatic.  

The Offset Knob

The CW tone you hear is the difference between the current PTO tuning and the position of the Offset knob.  The Offset knob can be an offset to either side of the current frequency (think of this as CWR depending on your band).  In other words the zero position of the Offset knob applies zero audio offset to the currently tuned frequency so you wouldn't hear a tone from a signal with zero offset.  You should have the Offset knob slightly to the left on 80m and 40m (LSB offset) and slightly to the right of zero for the USB bands.

The Zero Beat Knob

So with the information above in mind... Pressing the Zero Beat button defeats whatever the Offset knob is set to (effectively zeroing the offset).  When you are exactly on frequency with a signal the audio from the signal nulls (goes silent).  This null / silence is your indication that your transmitter frequency matches the other station.  

However I've found that the Null or Zero Beat is quite broad, such that you could be up to 250Hz off frequency based on where you leave the PTO in the Null. 
For my radio, on LSB bands, I press the Zero Beat button, find the null and then go past it (turning the knob to the left) and then just tweak it back into the null.  At least for my radio that works.  Maybe other Century 21s have a finer Q on the Null.  

After you have zero beat the signal you can use the Offset knob like a RIT. The range on that knob is really broad.  I think the manual said 5kHz so just a touch goes a long way unless you like to listen to CW with a ear piercing 2kHz, high pitched tone.

Here's a video demonstrating operating the rig...

TEN-TEC Century 21 -- Front Panel Controls


The Century 21 has full break-in QSK on at all times.  It is extremely clean with no discernable pops or artifacts.  One complaint I have is that the pitch and tone of the sidetone itself is fixed.  You can vary the volume through a little hole in the bottom cover to turn a thumb wheel, from very loud to just loud but you cannot change the pitch and it's a bit harsh sounding. 

The headphone jack on my particular radio is broken.  I need to open it up to resolve that before the wife uses a large heavy object on my beautiful new transceiver.


This video demonstrates the receiver selectivity of this old radio. 

Where is the S-Meter?

This is a bare bones transceiver with just the basics necessary for CW communication.  As far as information for the operator: Well there's an analog dial that gives you a rough indication (within 5kHz) of where you are transmitting, and an input wattage gauge for the drive and that's all.  Notably missing is a Signal Strength meter so the signal reports you send will be based on your ear, or how generous you're feeling at the time.

It's a little funny to me that I'm enjoying using this radio given it's lack of... well just about everything compared to my Elecraft KX3 whose tiny display indicates Signal Strength, Signal Relative to Zero Beat, SWR, RIT Offset, VFO A/B (down to a 10Hz range) Time, PA Temp, etc.  It just goes to show you how much modern rigs have that, when it comes down to it, isn't actually necessary for communication.


A bit of history about TenTec QRP radios and the C21 from a 1977 magazing article...


  • Frequency Coverage: 3.5 to 4.0; 7.0 to 7.5; 14.0 to 14.5; 21.0 to 21.5; 28.0 to 28.5; 28.5 to 29.0 MHz. (Crystal not supplied for 28.5 to 29.0 MHz, but available as accessory, Model 273.) Note - Early models only included crystals for 3.5, 7, and 14 MHz bands. Crystals for 21 Mhz and 28 Mhz bands were available as optional Models numbers 271 and 272.
  • VFO Frequency Stability: less than 20 Hz change per degree Fahrenheit, averaged over a 40o change from 70o to 110o, after 30 minute warmup. Less than 20 Hz change from 105 to 125 VAC line voltage.
  • Direct Frequency Readout: Marked in 5 kHz increments from 0 - 500 kHz, MHz markings for each band displayed.
  • Tuning Rate: Approximately 17 kHz per revolution of main tuning knob.
  • Power Requirements: 105 - 125 VAC, 50-60 Hz. 10 watts receive, 100 watts transmit.
  • Semiconductors: 25 transistors, 26 diodes, 5 integrated circuits.
  • PC Boards: 4 plug-in types, 6 integral.
  • Construction: Rigid aluminum chassis and sub-panels. Aluminum case. Grey front panel, black textured vinyl cover.
  • Dimensions: HWD 6.125" x 12.5" x 12"
  • Weight: 15.5 lbs


  • Sensitivity: 1 uV or less for 10 dB S+N/N.
  • Selectivity: Three position; 0.5, 1.0, and 2.5 kHz.
  • VFO Frequency: 5.0 to 5.5 MHz. Double Direct Conversion.
  • Antenna Input: 50 ohms, unbalanced.
  • Audio Output: 1 watt @ 8 ohms, less than 2% harmonic distortion. Built-in speaker; PHONES jack.
  • Offset Tuning: Approximately +/- 5 kHz, defeatable with ZERO BEAT switch.


  • DC Input Power: 70 watts
  • RF Output Power: 25-30 watts, typical.
  • Output Impedance: 50 - 75 ohms, unbalanced.
  • T/R Switching: Full break-in cw with PIN diode switch.


Sample QSO... Listen to the lovely receiver but the horrible sidetone.

Update: Here's another QSO I made a few months later into learning the Code.

And here's yet another from Straight Key Night 2017.

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Some of this old beauty's insides...

As I use the rig more I'll try to make some recordings and post them in subsequent blogs but that's all for now.

So lower your power and raise your expectations

73 / 72
AA4OO (formerly N4PBQ)

Saturday, November 7, 2015

Can a Straight Key really Coexist with a Paddle ?

The Harmony of the Keys 

/kōəɡˈzist/ -- verb 
exist at the same time or in the same place.

Can a Straight Key coexist with a Paddle? 

Key  ☾☮ E ✡ ☼ † 
Ok, so I have my nifty 1977 Ten-Tec Century/21 and it has one CW key input and of course at its age it has no built-in electronic keyer, so no paddle for you buddy.  I like to switch back and forth between a paddle and a straight key during a QSO so I went looking for an electronic keyer that would allow me to have both types of keys attached at the same time without touching any switches or controls.  Some people simply plug both keys into a Y-Cable and then switch the keyer on in the radio when they want to use the paddle but I switch frequently enough to where I don't want to have to change any settings and I especially don't want to go into a menu (I'm a confessed menu hater).

A modern marvel... The HK5A HAM KEYER

Aren't those gold tone knobs lovely... this must have been the Deluxe Model
This electronic keyer dates somewhere between 1975 and 1985. The St. Louis Ham Radio Center primarily made and sold keys, both paddles and straight keys that were knock offs of the old Brown Bros. keys.  One of their models was a "dual-key" with both a paddle and a straight key on one base so I assume that with this in mind they created the HK5A with dual-inputs allowing both a straight key and a paddle to be attached simultaneously.  The HAM KEYER uses the clever Curtis 8044 keyer chip which is long out of production.

This keyer has no provision for memories but I don't expect to do contests with the old Ten-Tec and my memory is still fine so no worries... mmm,  now what was I saying?  

The HK5A has a sidetone speaker with a volume and pitch (tone) knob.  It's not terribly unpleasant sounding, certainly no worse than the square-wave sidetone of the Century/21.  Maybe I'll set it five semitones lower than my Century/21 for some sidetone harmony.  The keyer weight knob has an enormous range and can turn your DITS into longer DASHES than the DASHES themselves so just a dab will do ya on that one, some component is probably out of spec inside the old boy.  The far right knob turns it on/off and lets you turn side tone on (with Tone) and the last position is key-down for tuning without touching the key.

So it's a fairly normal keyer with the added bonus that it has outputs for both direct keying and grid keying for older rigs with high plate current, that is assuming you don't want deadly voltage on your key.

The business end

On the back of the keyer you can see the outputs for grid and direct keying as well as the inputs for the straight key, paddles and a funky 2.5mm T/R 6v power supply plug.  
Paddle and Straight inputs, outputs for both Direct and Grid rig keying

It can also be powered by 4 internal C-Cell batteries which I've read last for ages so I went with that option rather than deal with RFI in one of my 6v wall-warts.  If it turns out to be power hungry I'll put a different plug on one of my old 6v wall-warts and try to choke it sufficiently to keep it RF free.  Best of all these old keyers come up frequently on auction sites and usually sell for very little.  I got mine for $16 + postage. 

So the HK5A HAM KEYER is the ticket to key coexistence.




Other options?

There is another option for wiring manual keys together with an external keyer that only has a single key input.  You can wire in the manual key(s) in parallel with the output of the keyer.  So you could use a Y-Cable at the output of the keyer and then the transceiver would be triggered by the keyer when a paddle is used and also be triggered when a manual key when it is used.  The only real disadvantage is that you cannot use the keyer for sidetone of any keys that are wired in parallel with its output.  

If you are using a rig with an internal keyer and only one key input there really isn't an option for two keys at once without changing a setting in the rig, that was the genesis of this article and the sister article for the KX3 two-keys-at-once.

That's all for now

So lower your power and raise your expectations
Or the way my posts have gone lately I should say "So purchase your grandfather's era equipment and lower your expectations, hi hi"


Thursday, December 15, 2016

QSO fun with a C21

It doesn't get much simpler

After dinner tonight I headed up to the shack to make a couple of QSOs.  I felt nostalgic and powered up the old TenTec Century 21 rather than one of my modern radios.  

My Vibroplex Bug and Kent Hand key are connected in series and I plugged into the straight key input on the back of the C21. I tuned as near to 3550 kHz as I could determine from the somewhat vague VFO dial and listened for a clear frequency.  I adjusted the output until I was producing somewhere around 10 watts to my lovely, no-tune OCF Dipole.  This old radio doesn't have a tuner so it's nice to use an antenna that is resonant on the bands the I use.

I turned on my camera, sent my call out once and was immediately answered by Dick (WB3AVF) up in Pennsylvania.  Turns out he was using a Standard Vibroplex bug that is very similar to mine.  It was my first contact with WB3AVF and we had a nice chat.

Fired up the 1977 TenTec Century 21 for a couple of old-fashioned QSOs

Switching the keys around

Dick and I had a couple exchanges and then he switched from his Vibroplex bug to a straight key so I followed suit on my next exchange, using my ever so clackety-clackety Kent Hand Key.

Vibroplex Bug and Kent Hand Key... both date to long before I became a Ham

The joys of an old radio

If you watch the video you'll note me chasing around the caller with the TenTec's audio offset knob.  I wasn't changing frequency with the VFO, I was trying to keep his signal in the audio bandpass sweet spot on the C21.  Unfortunately, my offset knob has become extremely touchy; as you can see in the video.  When I barely touch it, it will jump by a 100 Hz so it's fiddly to use.  I need to open up the rig again and find the out of spec components.  Maybe a Christmas project but I'm kinda hoping I get a new transceiver kit to build this year.  I keep planning to work on the C21 but other projects get in the way.

You can hear that the VFO drifts a bit as it warms up. That was the first QSO after turning on the radio so you'll hear after every exchange that Dick's station had dropped in frequency a bit and I was compensating with the offset knob.  He probably had to chase me about 300 Hz during out QSO while the components stabilized.

This C21 is from 1977 and uses a direct conversion receiver allowing you to hear the same station on both sides of the zero beat.  That makes for interesting zero beating...  I normally tune from a higher frequency to lower while keeping the offset set to the high side of the zero beat, about 600 Hz.  That way as I approach a signal and it's pitch decreases from high to around 600Hz I know that I'm on the correct side of the pass band.  If QRM becomes bad during the QSO I'll use the offset knob to jump to the other side of the zero beat and often that gets me away from an interfering station by moving their received "pitch" out my audio passband.  It's more complicated to explain than demonstrate.  I didn't do that during this QSO but, trust me it works well unless the band is really crowded.

The offset knob works on both sides of the signal due to the direct conversion receiver in the C21


Band conditions on 80m were nice tonight.  I was outputting around 10w and Reverse Beacon network showed that I had good coverage to the North which my antenna favors.
I saw decent RBN spotter reports even though I was using low power and my antenna is compromised for 80m use since it is only 25 feet above ground at it's apex and slopes down to 10 feet AGL on the long end of the OCF.

You can see that one report was as high as 34 db over noise and 9 reports were 20+ db over noise range, so not too shabby for the poor solar cycle and low power.  There were some faint static crashes, which are frequent on 80m especially in the summer but they weren't bad tonight.  

I really enjoy the 80m band in the winter for ragchewing in the evenings. Other than QRN it's much lower band noise for me and not as busy as 40m.  I can use my older radio without trying to dodge QRM from close packed stations.

Right after the first QSO was over I was called from different station, also in PA, and that operator was also named Dick.  So it was an evening of QSO coincidences.   

Make some calls and see how many QSO coincidences you enounter.

Ah.. the sounds of a 1977 QSO... 

I hope you make it to the Kent Straight key clacking toward the end

I'm glad I had the camera rolling when WB3AVF answered my call.  I enjoy listening to a two-way Vibroplex bug QSO.  I know the copy is a bit rough in a couple of places since I had not warmed up prior to the QSO. I normally need 15 minutes or so of time with my bug to smooth out my sending, and that didn't happen tonight.  If I can make the time, I'll add a transcript. Or if someone wants to send me a transcript of this QSO I'll give them full credit and include it here.

That's all for now...

So lower your power and raise your expectations... (and use old crufty radios)

Richard, AA4OO

I've added a video detailing operation of a Century 21...

Tuesday, October 10, 2017

CW tone comparison C21 to KX3

The old ways are sometimes best

This is a short one.  I haven't found much time lately to enjoy the hobby, but the past few evenings I've been firing up the old Ten-Tec Century/21 and just listening to CW while I tend to other duties.   Tonight, I managed to find time before dinner to have a brief ragchew with fellow SKCC member WV8DH (Dave in West Virginia) using my old rig.  It reminded me how much I enjoy the sound of CW coming out of that radio.

I was too lazy to set the camera up to capture the QSO, but after the QSO I dropped down the band to find a good ragchew going on and grabbed my smartphone and shot a quick comparison of the CW tone presented by the 40 year old TenTec radio and my new, modern, Elecraft KX3. 

After listening to the video I realize that a lot of wonderful sound, including harmonics are not captured by the microphone on the phone and can't be heard in the video.  Nonetheless, I think you'll agree that the older rig has finer CW audio. It's certainly more pleasant to listen to for long stretches.  The KX3 audio still wears me out if I operate more than an hour.  I wrote a detailed post comparing the KX3 to the Ten-Tec Eagle last year that pointed out what I believe the culprit of the tainted audio on the KX3.  The Eagle is presently off the desk and if anything the older Ten-Tec Century/21 sounds even better than the newer Ten-Tec Eagle.

But here's the brief, badly made smartphone video comparison of the C21 and the KX3...

Comparing CW tone from TenTec C21 to a modern Elecraft KX3

That's all for now.  I'm going to be reviewing a nice bug that a friend has loaned me soon.

That's all for now...

So lower your power and raise your expectations

72/73 Richard  AA4OO

Saturday, January 27, 2018

Before transistors there were TUBES

Oh Boy, what have I gotten myself into


A few months after re-entering the hobby in 2015 I picked up a TenTec Century/21.  It has been one of my favorite radios to operate and it is the most aesthetically pleasing radio I own.  After working with it's older (circa 1977) discrete transistorized technology and debugging some of it's problems, I became interested in building kits to learn about electronics.  I built a number of radio kits from different sources and some of the mini-module kits from Elecraft.

But I kept wondering about tube radios.  I came to the hobby well past the tube radio era and although I've read a lot about valve technology I didn't have any first hand experience.  I kept watching auctions for old Heathkits and Military radios and even bid on a few but lost the bids.

This past Christmas I decided that in 2018 I'd do something about this lingering interest.  I knew I'd eventually want to operate one mobile because, well that would certainly make it harder.  The power requirements of tubes are orders of magnitude greater than the QRP transistorized rigs I'd purchased.  Not knowing what I was doing I figured I could re-work an old Heathkit HP-13 power supply to give me what I'd need for an old military radio like the GRC-9.  

Heathkit HP-13a

Unsurprisingly, I was the only bidder and got one for $30 along with the odd grove power connectors that it uses. But I didn't do my research, and soon learned that the magic for these high voltage power supplies lies in the very specific design of their transformers.  In the case of the HP-13 it is operated much like an old military vibrator power supply with two germanium transistors acting as the vibrator.  Current is applied to to the core until it saturates and then a specific voltage determined by the number of turns is generated, the saturation drops the current to that winding and it starts over with the other transistor and the other winding.  I couldn't easily, or practically lower the 800v high voltage down to 580v required by the military radio I wanted and even the low voltage windings produce 300v and 250v respectively which is far beyond the 105v needed by the military radio.

I was warned off actually purchasing a military vibrator power supply due to a number of issues so I decided I'd start out with the radio this supply was designed for, a Heathkit HW-101.  All the electrolytic capacitors have to be replaced, and I plan to replace the diodes to be on the safe side as well.  I'm hoping the old transistors are still serviceable as I can't find any information on direct replacements for those.  I've ordered the replacement caps, diodes and resistors so I'll see how my refurb of this old power supply works out.  Working with voltages that can kill me is a bit daunting and I'm being very careful with the limited power-up tests I've performed so far.

Heathkit HW-101

That brings me to the newest arrival.  If you read my blog you know I like to do photography and it's no fun to photograph ugly radios so I kept watching auctions for HW-101s that were in good cosmetic condition.  I knew I'd have to do a good bit of refurbishment on whatever I ended up with but at least I could start with a "looker".

Heathkit HW-101
I plan, of course, to use it primarily for CW.  I'm aware that this radio is NOT particularly pleasant for CW due to the clacking relay as well as the poor filtering, but I've gotten accustomed to hearing lots of CW stations at once while working with my Century/21 so I think I can adapt.  All my other radios have full break-in so this will be a challenge to deal with, but I'm up to seeing what it was like for old time hams.

Crystal filter
While it has a crystal filter, 6dB of filtering at 400Hz will not offer much rejection to the out of band signals.  I guess I'll see. 

Admittedly this is far from QRP radio but I will endeavor to operate mobile at least a few times just for the experience.  I plan to operate at QRP levels to the extent I'm able.  There's just so much for me to learn.

If I don't maim myself or burn my house down, be on the lookout for posts as I resurrect the power supply and the old girl and get it on the air.  I have some ideas for photography involving glowing tubes that I think will be fun to figure out.  My bigger challenge is that I have no room for this thing at my operating position, so I'm trying to figure that out as well.

So drop me a line if you have restoration experience with these rigs.  Of course I'm reading what I can and look forward to learning how to align the transmit tubes and all the things I've had absolutely no experience with in the world of transistorized radios.

That's all for now

So warm up your tubes and raise your expectations

Richard AA4OO

Friday, November 6, 2015

The Amazing 80m Multi-band Windom

Happier than a slinky on an escalator

OCF Dipole resonant on 7 bands

The Windom (or OCF Dipole if you prefer), offers a true multi-band, experience without much use of a tuner.  
The tuner in the images below is in BYPASS mode.  I'm using it to demonstrate the resonance of the Windom on different bands.  If you're not familiar with reading a cross-needle meter, the needle pointing to the left is the forward power (transmitted) and the needle pointing to the right is reflected power.  You read the intersection of the two needles to determine the SWR.  The red, curvy lines in the middle are the SWR based on the intersection of the two needles.  It sounds complicated but it's so easy to view at a glance it's much nicer in my opinion than a digital SWR display.
The meter below is set to the 30w range rather than  300w so you are seeing 5w there rather than 50w

This antenna is resonant with a SWR  of 1.1 or below on 80m, 40m, 20m and 10m.

80m SWR 1.1
SWR 1.1 on 80m at 3.530 MHz

40m SWR 1.0

SWR on 40m at 7.030 MHz (forgive me I was transmitting 10w on the Ten-Tec)

20m SWR 1.1

SWR under 1.1 on 20m at 14.060 MHz

SWR on 10m 1.0

SWR 1.0 on 10m at 28.030 MHz

15m is the worst with a SWR of 2.5 so it requires tuning

SWR on 15m 2.5 at 21.030 MHz

Who Cares?

So in the days of auto-tuners maybe this isn't that big a deal except that SWR does eat some power in the coax and if your running low power then your 5w may become 2w without you realizing it.

For older rigs that don't have an auto-tuner like my Ten-Tec Century/21 I don't have to worry about tuning at all except on 15m.  It's also nice to just have the simplicity of transmitting into a wire without a inductance / capacitance circuit in-between.

Band change without re-tuning (except 15m)

So show me the antenna...

Images of wire antennas are not terribly interesting but here you go:

The apex of the antenna is hung from the peak of my roof.  The coax attaches to a 4:1 current balun with the positive side of the balun feeding the longer wire. The shorter wire is 44 feet long and is supported at the apex height of 25 feet by a birch tree in the front yard.  The long end of the antenna is 89 feet long and runs into the back yard. It is supported 12 feet off the ground by a fiberglass pole until I get a piece of wood permanently in place. 

To tension the wire I have a support rope in the front tree attached to a 5lb weight.  This will eventually wear through the rope and when it does I'll probably do it right and get a pulley up there. The support rope for the long end of the wire at the fiberglass pole goes through a pulley to a spring for tension.
80m Windom (OCF Dipole) hung from the peak of the roof
The line heading to the window is just rope that goes into the window so that I can pull it back to work on it, detach it, etc.
Long end of the wire (89 feet) is supported by a fiberglass pole about 12 feet agl

Back story

My 40m Windom had lain under the bushes for a number of years before being resurrected this past summer.  It was bare wire and the balun was likely wet, corroded and filled with critters.  Nonetheless I made hundreds of contacts using it QRP so I'm not knocking it too badly.  The issue I had was that it had gone out of resonance for a good match on the bands it was supposed to support and I had to use the ATU in KX3 to touch it up.  On some bands the SWR was as much as 5:1 so I was losing some power in the 100ft run of coax to my meager QRP radio.

When I recently picked up an old Ten-Tec Century/21 it had no auto-tuner and I'm not a big fan of manually tuning my MFJ Deluxe Versa Tuner II no matter how Deluxe it is.  It's just time consuming and if I answer a QSO after tuning around and see that I need to re-tune, well that's just a bummer with a manual tuner.  I'm trying to keep my costs down and using an auto-tuner with the old Ten-Tec just didn't seem right anyway so I wanted a resonant multi-band antenna.

I had an extra 4:1 current balun from years past and a fellow ham had recently given me a good supply of insulated wire.  I also wanted to get an 80m so that all played together to putting up an 80m Windom in place of the 40m Windom.   Only this time using some fresh parts.  That was a little over a week ago and I've had some time to play with this new antenna.

I've received good reports and finally am able to operate on 80m without the tricky tuning of my 40m Doublet in the Attic.

So that's all for now

Update (11-20-2015)
I originally only tested the antenna with my Ten-Tec C21 which had no WARC bands.  I was running the KX3 at the house yesterday and found that it also presents an SWR below 1.2:1 on 17m, 12m and 6m.  That makes it resonant without tuning and with a super low SWR on 7 bands (80, 40, 20, 17, 12, 10, 6).  That is truly an amazing antenna for those who don't like to use a tuner.  It requires tuning on 30m and 15m as it is natively 4.5:1 on 30m and 2.5:1 on 15m which is well within the capability of any built-in auto-tuner and easily matched by a manual tuner.
Update (2-11-2016)
I have been puzzling over the good performance from this antenna and updated information in this post:Feeling Skippy on 80m

Lower you power and raise your expectations


Sunday, January 8, 2017

My TenTec Eagle sounds better than my Elecraft KX3

Your eardrums will thank you

Coming back to the hobby in 2015 I re-entered as a CW / QRP operator and I searched for a good QRP radio.  The Elecraft KX3 certainly qualified and it has been a great radio to use, especially when portable.

Elecraft KX3 -- stellar radio for portable QRP operations

But a few months after getting my KX3 an old TenTec Century/21 found it's way onto my desk and through numerous blog entries you may note that for some reason I kept gravitating to use it rather than my KX3 when I operated from the shack, even though the KX3 beats the old C21 technically in absolutely EVERY regard.  I just enjoyed operating CW with the old radio more than the KX3. I couldn't explain why.

Fast forward to late March of 2016.  I purchased a used TenTec Eagle from my friend AA4XX and began using it as my primary radio when I wasn't portable.   Here again the KX3 trumps the Eagle in nearly every technical aspect and offers dozens more features.  I just kept gravitating to use the TenTec radios rather than the Elecraft.

I used the my KX3 for Field Day in 2016 and after I packed up and brought it home the KX3 stayed in my backpack and only came out for portable outings.  It did not go back on my desk.  The KX3 cried little electronic tears while the Eagle gloated...

Ten-Tec Eagle -- compact / simple HF transceiver

Why no love for the KX3?

Time passed, and over the new year break I got to thinking about what I missed about having my KX3 on the desk; like its RX/IQ output for HDSDR and the ease working DX splits using it's dual watch capability and it's integration to logging applications like the ability to trigger CW macros from my logging software.  The list of "nice-stuff" goes on and on since the KX3 contains multiple kitchen sinks...  So I re-organized my desk to make room for the KX3 again and operated with it exclusively over the past few days...

I was getting ear fatigue and my ears rang in the evenings.  This was not the sort of ringing in the New Year that I wanted. I had been previously operating the same amount with the Eagle over the past month without the earaches.  Something was amiss.

Had I finally discovered why I keep going back to my TenTec radios?

Audio, Audio, Audio

So over time, even when I switched back and forth between radios there was a subtle "ouch" occurring when I used the KX3.  I enjoy CW and digging out weak signals can be fun... or it can be painful.  I guess when I sat down to use a radio and my hand hovered between the "Oh-so-feature-rich" KX3 and the "Nice-personality" Eagle my brain was saying "choose the nice personality" you're happier that way.

But there was a underlying reality to the choice I was making.

Just the facts mam

I used an audio frequency analyzer to capture audio from each radio by sandwiching the microphone in my headphones.  It hears what I would hear.  And the graphs tell a tale.

Below is one graph for each radio.  The RED graph line in each chart is the averaged "peaked" frequency output audio during the same QSO.  Ignore the green line as it was just the instantaneous  audio at the time I froze the display between takes.  The CW sidetone on each radio is set to 620Hz.

I re-ran this capture for each radio a few times during a lengthy ragchew between two stations.  The signal strength was around S5-S7.  It wasn't a strong signal which is typical of what I work, especially as the Solar cycle winds down.

I tried the captures with and without noise reduction on each radio.  The RF was rolled off as evenly as I could determine for each and both were set to a DSP filter bandwidth of approximately 400Hz.  Both radios were using the same antenna and everything was as similar as I make it.  RCVR EQ was set flat for the KX3.

Elecraft KX3 CW audio (ignore green graph line)
Ten-Tec Eagle CW audio (ignore green graph line)

The CW audio output from each of the two radios is distinctive

KX3 audio demonstrates
shoulder noise
Eagle has clean audio
There's clearly a CW signal peak around 620Hz in each radio but the KX3 shows a significant shoulder of audio just 9dB down from the peak below the center frequency 

Whereas the Eagle has a clear peak presenting a narrow tone range at the sidetone pitch with narrow shoulders down to the filter width.

Confirmation of my subjective tests

When I saw this I literally said "Aha!"   

This confirmed what my ears and my subconcious had been telling me.  The KX3 is more fatiguing to listen to than the Eagle because it presents more noise in the audio or at least a wider audio signal given the same DSP filter setting.  I've always remarked about my TenTec radios that their CW seemed to float above the noise.  I believe it's related to the cleaner audio filtering. The TenTec Eagle just has cleaner audio out of the box. It has no audio adjustments beyond AF and NR, no menus for fine tuning.  My old TenTec Century/21 sounds the same when using its 500Hz selectivity setting. 

In my opinion Ten-Tec just got CW right.

Yes, I have tried using the KX3 RCVR EQ settings to reduce that lower frequency noise and the problem IMO is that the EQ is more for SSB audio.  I think the Q for each setting is too broad and when I try to reduce the low frequency noise IMO it just makes the audio sound mushy.  I just can't get as "clean" sounding CW tone out of the Elecraft as I can the Ten-Tec.

OK, "sound" is a subjective thing.  No two people will hear the same thing the same way and frequencies that bother me may not bother you, but it seems pretty clear from the graphs that the CW audio from the KX3 doesn't match the Eagle.


Admittedly, my test involved a very small sample size of one radio from each manufacturer.  It's just that I'd put the KX3 back on the desk after a many month absence and my ringing ears got me to investigate the cause a bit more scientifically.  

I will continue to use the KX3 for portable ops because it is a great self-contained radio and when I work portable I usually operate for much shorter periods so the audio doesn't become an issue.

Man, I hope Ten-Tec can come back from the grave. They sure made some fine radios for CW operators.

That's all for now...

So lower your power and raise your expectations

Richard AA4OO