Where did my power go? My Elecraft W1 power meter has been absent from the antenna chain for a while due to a jumper cable shortage when I last reconfigured my shack. But now the W1 meter is back in the chain and it revealed something a bit worrisome about the 1Watter transceiver...
I've had a bunch of QSOs using the 1Watter both in the shack and in the great outdoors. The 1Watter is my first home built transceiver (albeit from a kit) and has been a great learning experience. It is called a 1Watter (or 1H2O as Diz calls it) because it nominally produces an output of 1 watt.
The Elecraft W1 power meter is a nice, inexpensive QRPp to QRO meter because it measures from 150 watts all the way down to 150mw.
The little 1Watter transceiver does indeed produce just a hair over 1 watt when it's first powered up. Tonight I tossed my call out on 7030 kHz and was promptly answered by N4DR up in Maryland. He was running a YOUKITS TJ5A at 5w. When we started the QSO my W1 meter showed that my 1Watter was outputting between 900mw and 1w to my mighty attic antenna.
Then by the second exchange in the QSO I noticed my output power dropping down to 700mw. By the end of our ragchew my 1Watter output had dropped to 500mw.
Power meter in background showing 500mw by the end of the first QSO
As I ended that first QSO I was called by another station (AF4YF) who was running a 2 watt homebrew xcvr. And by the end of that QSO the 1Watter was producing less than 300mw. I felt that some investigation was in order.
Heat is the enemy
The 1Watter uses a 2N5109 NPN RF transistor for a final. Transistors really are not fans of heat.
The maximum power output available from a power transistor is closely linked to temperature, and above 25°C falls in a linear manner to zero power output as the maximum permissible temperature is reached.
My 1Watter kit included a friction fit heat sink, seen at the top of the photo below. But apparently this heat sink either saturates quickly or doesn't have sufficient surface to conduct away the heat. My enclosure is not vented but it is alumunium and I don't feel any appreciable temperature rise above ambient so I don't think venting is in order yet.
I allowed the 1Watter to rest for 30 minutes following the QSOs, still powered but not transmitting. That only resulted in the output power getting back into the 700mw range. I'm considering increasing the bias to start with a higher transmit power so that it will maintain 100mw but I'm afraid of destroying the transistor. I might also try some conductive paste but it's messy and I'm not sure it will help if it can't be pressed between two surfaces.
I'd appreciate any constructive suggestions. I'm still a noob at this electronics stuff.
But the real moral of the story is...
Band conditions on the evening of this QSO
So as I sat here wondering why my 1 watt radio was only producing a 1/2 watt now, I reminded myself that I was having extended QSOs using a (now) 500mw radio with other QRP operators (5w and 2w). I was also using my attic antenna, not some multi-element beam on a tower. Band conditions on 40m were also a limiting factor tonight (see snapshot at right).
These were not simply swap 599 TU QSOs, we were exchanging information on multiple go-rounds with solid copy.
So if you're reading this blog you likely have some interest in QRP. Hopefully this is just yet another reminder that we often don't need as much power as we think we do for communications. I was getting discouraged this summer due to the decreasing sunspot cycle and thinking "I'm gonna need to operate QRO more and likely get a real antenna put up in my yard". But it's times like this with my 1Watter that keeps reminding me to lower my power and raise my expectations.
So lower your power and raise your expectations...
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.
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.
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
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.
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
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
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.
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
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