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