Resistance IS NOT FUTILE

The Beautiful Genius Load

In this age of hyper-political-correctness it seems that I should not call my homebrew contraption an "Ugly Dummy Load".  

Ugly is so negative. It probably has a great personality and an inner beauty all its own.

And calling it a dummy is sooo degrading.  Why that's akin to calling it a Dolt, a Dullard, a Dunce, a Fool, a Blockhead, an Ignoramus, a Numbskull or a Simpleton.

So in the spirit of the age where Everyone Gets An Award

Behold the "Beautiful Genius Load"

Beautiful Genius Load

Construction

Up to now I only had one dummy load and it was built into my MFJ Deluxe Versa Tuner II so I thought it was high time to have something a bit more portable.  I already had the UHF connector in my junk box and lots of spare 12g solid copper wire.  So I ordered some 2w/1000ohm 1% resistors for 40 cents each and built the contraption above for about $10.  The bare copper wire is soldered to the bulkhead connector; one wire to the center conductor and the other to a screw terminal.  I simply wrapped the resistors leads around the bare wire and soldered them in place.  In the near side of the photo it looks as though they are not soldered but that is because it was flipped over when I soldered that side.

Concerning 1% resistors... I could have used 5% resistors rather than 1%.  The number of resistors would have averaged out the differences but I like the blue color and everyone wants to be a 1%'er.

Exhaustive parts list:

• UHF bulkhead connector
• 20 x 1000ohm 2watt resistors
• Two stout gauge copper wires

Not an especially good design

This is not a very good design for a dummy load due to its length.  The two parallel wires will generate some capacitance especially at higher frequencies but for ease of building it can't be beat.  In the following section I show the results on the analyzer and you'll see that there is some capacitive reactance that causes the SWR to be 1.1 starting at 14 Mhz.  This certainly isn't ideal but it is sufficient for most amateur uses.  If you think you need totally pure resistance all the way up to 28 Mhz you'll want a different design.

I may place it in a 2 inch PVC pipe with some holes drilled for ventilation to give it some mechanical stability but the heavy gauge wire seems plenty sturdy for now.  Of course, while it's in use you want to keep it clear of metallic objects and not touch it during transmission.  Also it will get HOT after extended use so don't go and grab after you've transmitted into it without determining if it will burn you.

Performance

Well it works mostly like you'd expect a Dummy... errr Beautiful Genius load should.  The twenty 2watt resistors give me plenty of heat dissipation for QRP levels.  I transmitted at 5w into it for a full minute and it was just starting to warm. It should handle QRO loads up to 100w for a few seconds at a time as long as it's given time to cool down between uses.

The SWR is 1.0 on the lower bands and 1.1 - 1.2 on the higher frequencies...

80m SWR 1.0

40m SWR 1.0 

30m SWR 1.0 

10m SWR 1.2

15m SWR 1.1 

17m SWR 1.1

20m SWR 1.1

Make your own Dummy Load... errr Beautiful Genius Load

It's always handy to have a small dummy load handy. You can use more or fewer resistors depending on your needs.  Just remember the formula for calculating resistance is:

Calculating Parallel Resistance

You want to end up with 50 ohm as your total.  Also be sure to use resistors with decent power handling.  Soldering 1/8 watt resistors in parallel isn't going to give you much power handling capacity.

That's all for now

So lower your power and raise your expectations

72/73

Richard, N4PBQ

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

• AF1 Audio Filter
• BL2 Switchable Balun
• CP1 Directional Coupler
• W1 Powermeter

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.

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.

That's all for now... 

So lower your power and raise your expectations

73/72

Richard, N4PBQ

I've Got the Power

Elecraft W1 Power Meter

The Elecraft W1 is another fine mini-module kit from Elecraft.  It is an auto-ranging power meter measuring as little as 150mw up to 140w.  The 150 milliwatt to 1.4 watt range is an especially nice feature for QRP'ers. 

Elecraft W1 Power Meter

Building

I am new to building kits.  My first kit was from 4-State QRP (Regen Receiver).  This is my 4th Elecraft kit.  The instructions are very detailed and easy to follow and I especially like that they give you the resistor color and capacitor identification right there in the instructions without having to refer to a data sheet somewhere else in the documentation.

All the parts come in a single bag so there is a bit of sorting that you need to do when you receive it.  I use a big egg carton to sort and inventory the parts so that I can find them more easily.

This kit was a bit more involved than the other kits I've built from Elecraft.  It has a binocular toroid which is fiddly to wind, 3 ICs and a couple of resistor packs.  Lots of soldering.  The most tedious parts to solder are the tiny transistors. Those solder pads are really close together for someone new to soldering like me, but I took my time and everything turned out ok.  I worked on this kit a little at a time over 3 nights.  If you can follow instructions and have a steady hand you should be fine.  

The kit has some ESD sensitive parts so you'll want to be able to properly ground yourself and your equipment.  Make sure your soldering iron is ESD safe and that you are grounded.

Lastly, final calibration is performed using just a multi-meter.

Build options

The meter can be built in a number of different configurations depending on how you plan to use it.  The battery holder and BNC connectors can be installed on the top or bottom of the board and the BNC connectors can even be oriented vertically on the back side of the board.  If you plan to use it in an enclosure give some thought to the location of the battery holder and BNC connectors before you get to that part of the build.

I plan to use some stand-offs to mount it to the front of an acrylic photo frame that I already had.

An acrylic-angled photo frame can make a homebrew stand

Operation

The meter can operate from a 9V battery or from an external power supply via the barrel connector on the side. There is a small power switch at the bottom left of the board.

The top row of LEDs indicate power for a given range. The 3 LEDs mid way down the board to the left indicate the current power range.  The range can be automatic or set via a command through the serial interface.

The ranges are:

• 150 milliwatts to 1.4 watts -- Green LED
• 1.5 watts to 14 watts -- Yellow LED
• 15 watts to 140 watts -- Red LED

Computer interface

There is a 1/8" stereo jack below the power connector that provides a serial interface to a computer.  There is a command set for interacting with the meter as well as a sample application available on Elecraft's site that allows a number of settings to be modified such as peak hold and saved to the meter.

Elecraft sells a $15 serial interface cable kit.  What they don't tell you is that it has a DB-9 connector rather than a USB connector.  I don't even have a computer with a DB-9 serial port so buyer beware. You may want to skip their kit and build your own.  I happened to already have a DB-9 to USB converter but I'd preferred their kit to provide a USB connector.

Demonstration

Photos

3 ICs to solder and toroid winding... lots of fun 

LEDs indicate power in each range and SWR

LEDs indicate the power range being displayed

Elecraft W1 Power Meter

That's all for now

So lower your power and raise your expectations

73/72

Richard, N4PBQ

Get a taste of the RF coming and going

Elecraft CP1 - A tasty RF treat

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.

That's all for now

So lower your power and raise your expectations

72/73

Richard, N4PBQ

Elecraft BL2

Two Baluns in One

Elecraft mini-module kits offer interesting and useful, little devices and I am learning a bit more about Ham Radio and electronics as I build them.  I previously built the Elecraft AF1 audio filter and tonight I assembled the BL2 switchable balun.

Elecraft BL2 kit

I wanted a small, low loss, balun for use with ladder line and end-fed antennas that I could switch between 1:1 and 4:1.  MFJ makes a commercial pre-assembled switchable balun but I suspect that the quality of its cores do not match Elecraft's.

The kit is obviously an easy build.  The most time consuming aspect is getting the four stripped wire ends from the core all equally inserted in their tiny holes.

I tried it out with my attic doublet and the ability to switch between 1:1 and 4:1 made a difference on difficult to tune bands.

According to an email correspondence with Gary (AB7MY) at Elecraft...

• The ground lug is there to be used to bleed off static voltage on an antenna that is not DC or earth grounded.
• We don't recommend using the balun with an end fed wire. It will have too much loss.  The balun is for use with a balanced antenna and a low impedance of 200-300 ohms or less.

Too Fragile?

The only drawback is the lack of an enclosure resulting in a relatively fragile mechanical connection to the antenna and coax.  I had hoped the board would be thicker than average epoxy board with some mechanical reinforcement of the connectors but it's standard thickness and the connections are only held on by their solder points.  450 ohm ladder line is pretty stiff stuff and I saw the connectors flex on the board as I attached the antenna.

I will need to get it in an enclosure before much field use.

Summary

I enjoyed the simple build and winding the cores and tracing out the continuity.  I've been studying for my Extra ticket and learning more about inductance.  Building even something as simple as a balun is interesting to me.

Update 2-8-2016

N4HAY recently performed a thorough test on the BL2 to measure its loss and current balance capabilities in blog (http://zs6rsh.blogspot.com/) in this blog post.

Thats all for now

So lower your power and raise your expectations

72/73

Richard, N4PBQ

Just stand up

The "Nifty Accessories" KX3 stand

Nifty Accessories KX3 stand

The Elecraft KX3 is naturally at home in the wild

My Elecraft KX3 is an incredible radio in many ways.  It's small size makes it a marvel for portable operations.

The upward facing display of the KX3's short legs is ideal for remote, portable operations

But on the desktop it's short stuff

But for desktop operation the short rear legs make for a laid back angle that makes the display difficult to see and the buttons awkward to operate.  I home brewed a stand that I've used for the past few months.  It angled the radio more vertically but it was still low to the desk. 

The KX3 on my homebrew stand

The KX3 "Iron Throne"

I finally felt it was time to give the KX3 some love and give it a proper throne chair for its little princely demeanor.  The KX3 now has some height and sits more vertically.  Access to the face of the radio is much improved.

Here's a closer view...

If you have a KX3 and use it on a desk in the shack the Nifty Accessories stand is a solid addition to improve the ergonomics of your little jewel.  It can be ordered with enough space to clear an attached paddle or lower to the desk if you prefer but I wanted the additional height to get it above some of my taller keys.

One Suggestion... replace the paper clips

The stand comes with big paper clips to hold the KX3 to the stand.  They are a a bit difficult to properly attach with all the cables exiting the KX3 on the left hand side and they look ugly.

I replaced the two paper clips with a small bungee cord which I attach as a loop across the top of the stand.  The bungee cord connects to itself underneath the stand...

The feet of the KX3 then slip under the bungee cord.  It seems to hold it sufficiently and is easier to attach and remove the radio.  It looks nicer as well...

That's all for now

So lower your power and raise your expectations

72/73

Richard, N4PBQ

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