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
Conditions
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)
72/73
Richard, AA4OO
UPDATE:
I've added a video detailing operation of a Century 21...
Keys left to right Nye Viking, Kent Hand key, Vibroplex Original Bug, N3ZN ZN-QRP paddle, Palm Single paddle
My collection of keys has grown over the past few months and I find that I like each for their particular qualities.
Keys from left to right
The Nye Viking is somewhere between a traditional J-38 low style American key and a tall European style. At first I couldn't get any sort of coordination with it even after a couple hours of practice and it stayed in the closet for a few months. Eventually I wanted to leave a key hooked up to the old Century/21 so I didn't have to move the output of my external keyer so the Viking came back out. I've finally become accustomed to it and am even beginning to enjoy it as much as the Kent. I'm amazed at how different two straight keys can be.
The Kent Hand key continues to be my favorite key for straight key operation. The Kent is operated using your entire arm off the desk and when I send using it above 15wpm I get the entire desk shaking with the motion. My desk light starts casting dancing shadows across the equipment from the vibration and with the clacking of the key and the blare of the sidetone the world of CW becomes visceral.
The Vibroplex Bug remains at the center of the collection because I have some strange affinity for the quirky bug. I use it on every QSO where I hear another bug operator or with SKCC operators that are sending faster than 17wpm. It has a non-cosmetic, yet effective, weight added from an old steel spacer to slow it down to a range of 21wpm to 16wpm and some dental floss around the DIT contact spring to reduce the potential bounce which results in scratchy sounding DITS.
The N3ZN ZN-QRP paddle is a work of art and when I'm working higher speed CW it's my go-to key. The carbon fiber finger pieces and lightweight clickety action always puts a smile on my face. I keep it connected to the external Ham Keyer which has a handy knob to for quickly adjusting keyer speed.
The Palm Single to the right is magnetically mounted to a steel base a friend made for me. I pull it off the base when I go portable as it's my go-to key for all my portable operations. But when I'm at the home station I leave it hooked up to the keyer input on the Ten-Tec Eagle because the Eagle's keyer is only Iambic-B mode and I just can't get used to "B-Mode". Using a single, non-iambic paddle eliminates the weird timing of the B iambic mode. I really should learn mode-B since it seems to be standard on Ten-Tec and Kenwood radios.
The 3 stars in the center are the Kent Hand key, Vibroplex Original Bug and the N3ZN paddle
The 3 keys in the middle (Kent Hand key, Vibroplex Bug and N3ZN paddle) remain hooked up to the Ham Keyer and I move the output of that keyer to whichever rig I'm primarily using at the time. That keyer uses Iambic-Mode-A which I'm comfortable with and it debounces the scratchiness of the Bug. I hook the output of the keyer up to either the PTT line on the Eagle or the secondary key input on the KX3. When using the C21 I just use the Nye straight key.
Debouncing a Vibroplex Bug
Side story on the Bug... If you get a Vibroplex bug and hook it up to the PTT line of your radio you may find that you're missing DITS or that the output sounds broken or scratchy. The PTT line of many radios is not "buffered" meaning it is reacting to every contact closure. On a bug, the DIT contact is actually bouncing potentially hundreds of times a second since the contact force is so light and doesn't make a clean closure. Many keyers will filter out those multiple contacts or bounces. My old HAM KEYER weight control actually serves as a DIT weight control for the manual keys as well so it's ideal for use with the bug.
KE6EE offered me this nice explanation of what was going on:
The more usual term for the process of dealing with problems of contact closure is "debouncing." Google and you will find lots of interesting visuals and explanations.
The actual start and finish of contact closures and openings in switches, relays and keys, is not a simple off-and-on process but a series of "bounces." Dit contact closures on a bug are likely to be very bouncy.
Bug dit contact design and bug maintenance and adjustment are critical for minimizing bounce. Ops with Vibroplex-style dit contacts often put a piece of rubber or plastic foam in the U-shaped dit contact spring. The Begali bug uses a unique pointed and spring-loaded dit contact. Many bug ops, from my observations on the air, do not adjust their dit weight properly to minimize a scratchy sound.
Transmitter keying circuits are usually "debounced" in various ways, the simplest perhaps being to put a capacitor across the key contact circuit. A PTT circuit doesn't need to be debounced so it isn't. Keyers often have debounce circuits designed to be used with straight keys and bugs.
Try different keys
So if you are getting into CW try some different keys. I think you'll be surprised by the differences and find that your mood or situation will dictate the use of one key over another. Morse keys on the used market aren't expensive if you shop carefully so you can build quite a collection. They also tend to hold their value if you find that you've obtained a key or two that you just can't grok.
My ever changing station sporting a spiffy new chair
That's all for now
So lower your power and raise your expectations
73
Richard, AA4OO
The Universal 1Watter (also called the 1H2O) is a full featured little superhet radio transceiver that you can build for about $50. It doesn't come with an enclosure, a tuning pot, speed pot or an on/off switch so that will cost extra unless you already have some in the junk bin.
Some of the features include;
1 mighty watt of output
Good selectivity from the 3 crystal filters
A VCXO tuned frequency range for the 40m band from approximately 7,020 kHz through 7,039 kHz
A built-in full functioned keyer with provision for adding a speed pot and messages
Included command button accesses the functions of the electronic keyer
Natural sounding sidetone (nicer than my Ten-Tec Century/21)
The Build
The kit is delivered in a box and inside are a couple of brown paper bags stapled together. Inside one of the bags are a couple of plastic bags with the components. The other bag contained the header kit. The ferrite toroid mix types are separated in different unmarked plastic bags so don't mix them up (the instructions tell you which bag has each mix). If anything is missing the kit supplier (Diz, W8DIZ) is very responsive.
The kit includes both SMT caps and through hole caps. I tried to solder one of the SMTs but I didn't have the right kind of tweezers to hold it in position for soldering so I used the through hole caps.
SMT and through hole caps are supplied
This is the 3rd revision of the Universal 1Watter board and I was the first to build the 40m version.
While the schematic was correct, some of the instructions weren't sorted out properly for the 40m kit. I related issues as I found them to the designer and he promptly updated the online documentation.
I soldered the components and wound toroids as I had time over a few evenings and the initial voltage tests went well.
using through hole capacitors rather than the SMTs
some of the bits and bobs
build is progressing
close up
XTAL filters give it good selectivity
Everything except the final transistor
AGC circuit
Debugging
When the build was completed I connected the rig to an antenna and heard nothing.
The keying circuit and transmitter worked fine and I verified those functions but the receiver was deaf as a stump.
Thus began a number of days of investigation. Diz (the creator of the board) guided me through a number of debugging steps.
The first recommendation was to examine and rewind the binocular toroid balun that transformed the impedance from the xtal filters to the input of the U5 oscillator. He believed that I may had wound it incorrectly. I desoldered it and rewound it but that did not resolve the issue.
He then guided me through determining if one of the filter crystals or filter capacitors was bad. I desoldered a few components as a tests but that did not resolve the issue.
There are 3 identical mixer chips on the board. I swapped them around as there was a suggestion that there were some faulty chips in one of Diz's shipments.
I then took the board to my Elmer Paul Stroud AA4XX. He had a signal generator, Oscilloscope and RF detector. He traced the RF and all looked well but we still were unable to obtain any signal through the U5 mixer. Lastly we tried disconnecting the AGC transistor to see if it was clamping it and that didn't resolve it either.
Diz asked me to return the radio to him so he could take a look. After a couple weeks he emailed me saying he thought the BFO xtal might have a problem. But he later discovered that the oscillator in U5 was not starting up. Apparently the circuit design had a low Q and needed more current to get the oscillator working. He modified the design, adding a 16k resistor to the bottom of the board on U5 to get the oscillator going. After that all was well and he shipped the board back to me.
The FIX for all those problems required an extra resistor connected across U5
Learning from problems
Being the first person to build a particular version of a kit brings its own set of challenges, especially when you're as new to kit building debugging RF problems as I am. However I'm actually glad the kit didn't work right at the initial build. The process of debugging the board, was a great learning process. I studied the schematics and learned, as best I could, the function of each circuit so that I could better understand how to test it. During the debugging process Diz instructed me that although RF signal generators and scopes are useful you can tell a lot by touching a RF component with an inductive metal object and listening for a buzz or hum from the BFO. So all-in-all, even though the bug in the board was not due to a error on my part, I'm glad it occurred. I understand more about superhet radio design than I did before and more than if the kit had worked right off the bat.
On the air
After receiving the board back, I hooked up the frequency XCO potentiometer, paddle, command button, audio and output potentiometer and an external speaker. I then connected a 12v battery and heard the 1H2O keyer chip announce itself at power up in Morse "1 W".
Frequency control pot on the left
Volume control, output jack, cmd pot and paddle input
You can change speeds and modify settings via the command button which I have not reviewed yet. I also plan to add the speed pot so that I can easily change keyer speed without entering the command menu. For this first on-air excursion I was using it at the default startup 15wpm keyer speed. You can default the speed higher with a different resistor value. I have a resistor shrink wrapped and connected in-line to the blue-white wire coiling above the radio connecting to the speed pot terminal. In essence fixing the speed at 15wpm until I add the speed pot.
Ready to transmit
On the air... I was using my paddle out of the photo to the right of the Bug
First On Air QSO
I tuned around and found a strong station at the end of a QSO near 7030 kHz.
When he sent the final dit-dit I called and WD4AXJ answered my first call. He was in TN near Knoxville, and I received a 559. We chatted for about 10 minutes. Sorry about the blurry video. I thought I'd focused.
After I recorded this video I found an open frequency and sent out my call. Very shortly thereafter KD2FSHanswered my call and reported me as 599!
Whoo - hoo. 599 for my little 1Watter 40m.
I was transmitting using my 40m attic antenna. So deed restricted HAMs take note. You can build a one-watt radio and make contacts using your attic antenna. Haha.
You'll hear in the video there is some weirdness going on with the audio derived AGC. It is clamping down sometimes and is worse when I don't have the volume turned up very loud. When I began calling it clamped after every semi-break-in but didn't do it much after that. I'll have to look into that.
The AGC clamping may be a side effect of the increased gain Diz added to the BFO oscillator. I'll ask the forum.
Other than the AGC issue I'm super pleased with the little board. I touched the heat sync a couple of times after transmitting my side of the qso and it was warm but not really hot. It seems as though as long as you have a reasonable match to the antenna the power transistor should be happy.
My next steps are to get it in an enclosure and get it out to the Excalibur antenna site to hook onto that nice 40m doublet we put up a couple weekends ago. I plan to use my efficient little BLT tuner for that purpose. I will do a further review of the feature set on the keyer and record some more qsos for a later review.
Summary
The band was fairly busy and the little 1Watter did a fine job with stations on nearby frequencies. You can hear some getting around the passband but it is not bad at all. I'll do some tests to further define it's selectivity but at first glance it is far better than my old Ten-Tec Century/21.
My calls were answered quickly and I received good signal reports. It didn't sound as though the transmitter was drifting at all during the QSO. That's one advantage of using VCXO in the design. The disadvantage of using a crystal controlled oscillator for the frequency control is limited tuning range. The transmitter only has about a 18 kHz tuning range around 7030 kHz and I don't find many of the SKCC folks around that frequency but it is the QRP watering hole for 40m.
It is possible to shift the frequency with some capacitance changes but I think I'll leave it as is for a time and see how many states I can work.
Just imagine. This little $50 single band kit has good selectivity, a nice built-in keyer with a natural sounding sidetone, and lest we forget... You get a MIGHTY 1 WATT of OUTPUT. What more could a QRP ham need.
That one-watt of output was sufficient for all the QSOs I attempted tonight.
So lower your power and raise your expectations
72/73
Richard, AA4OO
UPDATE: 04/01/2016
I
am still having the AGC pumping issue and others on the list have
reported similar issues but only on receive. It happens to me when I
key unless I turn up the volume very high. I did get it installed in a
case but I still need to wire up a real power connector rather than
using alligator clips.
!Watter installed in a case
UPDATE: 04/05/2016
After doing quite a bit of reading I learned that the LM386 op-amp used in the 1watter
is rather notorious for audio oscillations. There are a number of
suggested fixes. I went with a 4.7uf cap connecting Pin 7 on U6 (the
LM386) to ground. That hasn't totally resolved the issue but it's much
less pronounced now.
cap fix for LM386 oscillations
I
have it in the case with all the proper plugs now (see below) so I'm
happy. I've been making QSOs every day with it and it continues to
amaze me and the stations that work me. It is stable as a rock with
regard to frequency and the large knob with the single turn 10k pot
seems to work well for tuning. I have enough control to vary the
frequency slightly without having to turn it too much. The tuning range
is only about 20kHz so just 3 frequency markers are plenty to let me
know what frequency I'm near. The selectivity is just fantastic for
such a simple little radio. Diz has created an inexpensive winner.
1Watter in enclosure with all the proper connectors for the case Information on case and knobs:
I've had the opportunity to bring another wonderful radio from Ten-Tec into the shack. The Ten-Tec Eagle.
Ten-Tec Eagle HF transceiver
The Eagle is NOT a feature laden radio and using it is a bit quirky.
There are no menus on the Eagle. The dual-function buttons you see are what you get. The multi-knob allows adjustments for the various functions.
What it does have that is so common with the Ten-Tec line of radios is absolutely wonderful sounding audio and beautiful full QSK with no strange audio artifacts at full-break-in. It is a pleasure to work weak stations. This particular radio has three 4-pole filters for the IF at 2.4kHz, 600Hz and 300Hz. They are automatically selected as the dedicated bandwidth knob is adjusted, resulting in smooth and clear filtering of CW stations.
I also have a Elecraft KX3 and while it has similar receiver specifications, listening to weak CW with it has a lot of digital artifacts that are not present on the Eagle. I can work a weak station with the Eagle and not be fatigued at the end of the qso.
It also has a nice ATU capable of matching up to 10:1 SWR antennas and of course supports SSB. It covers 160m-6m and can do FM if the 15kHz filter is installed.
Eagle beside its much older brother, the Ten-Tec Century/21
CW the way it was meant to be heard
The solar conditions have been extremely poor over the past week that I've used the rig and are likely to be this way for a few years to come. It's nice to have a rig that makes these poor conditions still enjoyable.
If you love CW do yourself a favor and try a Ten-Tec. They are pricey compared to other rigs and they do not come close competing on price-per-feature but Ten-Tec receivers make for amateur-radio bliss.
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:
UHF to BNC from the radio to the W1 Power meter
BNC to BNC From the W1 Power meter to the CP1 coupler
BNC to UHF From the CP1 coupler J1 input to switched T1 output to frequency counter
BNC to UHF From the CP1 coupler J2 output to the tuner
And other cables:
Serial cable from the W1 Power meter to the computer
12v power cables for the W1 and AF1 (unless I want to use 9V batteries)
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.
Summary
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.
I had some time this afternoon to assemble another Elecraft mini-module kit. This time it was the Elecraft CP1 directional coupler.
Elecraft CP1 Kit
Couple what?
Ah, so if your new to this like me you might be asking what does a coupler do? Well it sorta listens in on the signal going out (forward) and reflected (back) and is able to send an attenuated sample of the signal to other devices. It attenuates the sample by either 20db or 30db depending on how you build the kit.
The 20db version is good for signals 25 watts and less so that's the way I built it. It was easy to build but my glue under the second toroid wasn't strong enough and you can see it popped up a bit. Also the Elecraft instructions had one confusing instruction concerning mounting the toroids. The instructions say "... When wound and mounted correctly, the enamel wire will emerge from the top of each core and connect to the top hole at each inductor location". Well when you wind a toroid only one of the wires can "emerge from the top of the core" while the other comes from underneath. This confused me for a minute until I finally just went on with the install. Anyway, if you're a stickler for following instructions that one may cause a moment of pause...
The switches for the two outputs forward, reflected (J3, J4) are in the up position when they are not in use. When the switch(es) are in the up position the 50 ohm 3 watt resistor(s) take the place of the switched off output. Don't disconnect an output and leave the switch in the bottom position. I'm not sure what will happen... maybe nothing, probably a bit of a mismatch on the SWR, or maybe it could be like "Crossing the streams" in Ghostbusters. Your mileage may vary.
My uses for a coupler
My old Ten-Tec Century 21 has an analog VFO dial that gives me a good guess at where I'm at but I use an external frequency counter to give me more information. I had it sorta rigged my frequency counter to sample the signal from RF leaked on the shield but I didn't really know how much power I was sending to the counter so this coupler allows it, as well as other devices, to be safely connected to the transmitted signal.
I also plan to use the coupler for IMD tests using a oscilloscope and other projects. It's handy device to have in your collection.
My confusion
I will admit I am still such an idiot when it comes to understanding how this stuff works. After I built it I was testing continuity and saw that input/output (J1, J2) both showed a short from ground to center pin on both BNC connectors. I thought I'd mis-soldered something and spent the next two hours unsoldering components and trying to trace the fault...
There was no fault. The way this thing works is a bit of mystery to me but as best I can tell it simply reverses the phase of the signal coming in one side (J1) and leaving the other (J2) and as far as continuity tests go, EVERYTHING has almost zero impedance. I'm still bewildered but it's AC not DC so my continuity tests don't mean much.
But in the end - It works
I finally just resoldered it, scratched my head and thought I'd give it a try. I connected the coupler between my radio and a dummy load and transmitted a watt and noted that the SWR on the radio was fine. Then I hooked up my frequency counter and it worked like a charm sending an attenuated signal to J3 for the frequency counter.
My MFJ watt meter doesn't seem to be all that accurate but I did a power test with it both in-line and absent. My MFJ watt meter measures 300w / 30w so it isn't very accurate at QRP levels. But I noted a slight difference in power reported when the coupler was in-line. If I had to guess by "Mark-One-Eyeball" I'd say the coupler was stealing about 1/2 watt. Maybe a bit more so that's something to consider. I'll know better once I build my Elecraft watt meter since it's accurate down to a tenth of a watt.
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
I've been working a lot of SKCC CW stations during the holidays and adjacent stations really interfere with my ability to use the vintage Ten-Tec Century/21. Its built-in audio filter is relatively effective if the band isn't too crowded but if I'm working a station and others pop up within a 1kHz on either side I have a real hard time keeping track of which QSO to listen to. I wanted some relief from the relatively porous audio filtering provided by the old girl.
A kit from Elecraft seemed to be the ticket to better signal isolation for my old radio.
Elecraft AF-1 Audio Filter Kit
Building the kit
This kit is about $60 and is pretty easy to build There are a couple of ICs to solder so it will be easier if you have a temperature controlled, fine tipped soldering iron. Santa brought me a nice soldering iron for Christmas so this was my first chance to make some use of it. Everything about the kit is very straightforward and Elecraft has wonderful build instructions along with a well laid out board. Their instructions list components in the order that you will be installing them on the board, left to right and even include the color coding or numbering for resistors and capacitors right there in the instructions so you don't have to keep going back to look up the coding. I've only built one other kit previously and the Elecraft instructions are better.
My only gripe is that this kit has been out for quite some time, but for some reason they shipped me a Version "A" board that required a trace to be cut and a couple of jumpers installed to correct a board error. I would hope that they would ship new versions of the board but apparently you can get an old version. Next time I order a kit from them I may specify that I want the latest revision of the kit.
Performance
The board powered up and worked right as the last of the solder smoke was wafting away. I connected it to the Ten-Tec and tried to find some adjacent station operations to test against but the bands were not terribly busy tonight. I did manage to get a decent audio test on a calling station and created a video to demonstrate the board's capabilities.
Summary
This is the first kit I've built from Elecraft. It was a simple one. The instructions were excellent, the silkscreen layout on the board was straightforward and all the parts were in the bag. The kit does not come with an enclosure so it looks a bit unfinished and the knobs are a bit wobbly on their tall, plastic shafts. That is my only negative concern regarding the finished kit. Putting it in an enclosure would also require the battery holder to be moved to the bottom of the board to clear the shafts exiting the top of an enclosure. Certainly not a big deal but I would be willing to pay an extra $10 for a ready made enclosure because when I've tried to make them they look like junk.
But the bottom line is that if you have an older radio that lacks good filtering or you've built a homebrew radio that you want to be more usable on the air, the Elecraft AF-1 is an excellent addition. I think it is going to serve me well with my vintage radio. Now to find a project box to fit it.
My burgeoning QRP station was getting messy, having stuff strewn all over the desk, so I made a shelf from some junk laying around to give me some vertical space. It is much more organized now.
A shelf helps
Left to right top shelf:
Ozark Patrol Regen Receiver Kit, MFJ Versa Tuner providing both tuning and antenna switching duties, Two Position Rig switch on top (blue box), Ham Keyer (circa '78) electronic keyer
Left to right under shelf:
Yaesu HT connected to home-brew J-Pole in attic, two switching power supplies, VHF/UHF meter, Elecraft KX3, Ten-Tec Century/21 (circa '77), Homebrew frequency counter on top of TT)
Three keys:
Bencher paddles, Vibroplex Bug, Kent Hand Key
That's all for now.
