28 April 2009

Empirically obtain the vertical radiation pattern

How would you study the vertical radiation pattern of your omnidirectional antenna? You'd need a signal source flying over the antenna at any given angle, far away.

For VHF and UHF antennas you may find that HAM satellites are handy for this task too.

Depending on your location, some LEO bird will pass over your antenna at a good selection of elevation angles. The best pass is one that puts the satellite as much above your head as possible. An FM satellite is even better, since it provides a carrier of constant power, like AO-51 downlink on 70 cm.

So, make a prediction of an usable pass. Don't forget to check the satellite operating schedule, if any. Draw or print or write down a selection of time, elevation angle and frequency +/- doppler. Azimuth is not relevant if your omnidirectional antenna has a clear view of the horizon. Sit back and wait. Then look closely at the S-meter (better if analogue).

So far I have received AO-51 UHF downlink on two antennas, one shorter than lambda/4 and one 3/4 wave (a VHF whip). Both magmounted on the car. At a certain point I noticed AO-51 signal at S2 on my S-meter with the VHF whip, as much as I could get with the Moxon beam!

Back to the computer, I used MMANA to simulate this antenna at UHF. It was not a surprise to see that at 45° elevation this antenna has a 5.5dBi gain. Moxon rectangles are said to have about 6dBi gain, so we're in the ballpark.

As a conclusion, I can say the 3/4 lambda at UHF is good to receive almost any AO-51 pass above 10°. Unfortunately it is not enough to hit the satellite repeater with 5W. With a proper S-meter, the vertical radiation pattern of an antenna can be drawn per-points.


If you were having a CW QSO with me and received a sudden "SRI QRT", as SP3DGV got last night, it means I had to run off to the youngest child because she woke up and needed assistance (ie woke up and started crying for whatever reason).

Radio time is very limited these days, and a 6 weeks old baby (@ end of April 2009) doesn't help.

Apologies in advance.

22 April 2009

FT817 keypad - April 2009 update

I have added support for a status LED (green), that is ON when the keypad is in the main menu/idle. For single key press functions (such as A/B), the LED is always ON, while it stays OFF for those sequences requiring several inputs until data is sent to the radio (like direct frequency dial).
The LED is now shown on the updated schematic diagram, but its use is optional. It is not included in the bag-of-parts I am offering from time to time. I will soon release an updated free firmware that supports the status LED.

I have also implemented and tested few more functions: A=B, AGC control, PBT on/off, BK on/off, FaST tuning on/off, Split on/off, RIT on/off, Lock. The latter three should also work on FT-857/FT-897.

Hopefully soon I will be able to certify "common" Yaesu functions on FT-817, FT-857 and FT-897, so to produce a cross-radio firmware.

17 April 2009

First attempts at AO-51

I had wanted to check how easy are today HAM sats for a long time, until I decided to give them a go few days ago. AO-51 looked like a good candidate, especially now that with FT-817 I can receive UHF with a simple setup.

I prepared as follows:
  • calculated next passes on the AMSAT website according to my location,
  • picked a comfortable pass, that would fly high over my head (strangely enough, at the time I'm driving to the office!)
  • prepared a 1/4 wave vertical antenna for the magmount car base
  • located a clear spot to park
And.... right on time the AO-51 downlink signal started filling my car, even just above the horizon. It was audible for the whole pass, altough did not move the S-meter (on my non resonant antenna).

For another pass few days later I had assembled a Moxon directional antenna (two elements, folded), and tried again. While it did improve the strenght, sitting on a concrete floor created a lot of reflections and I could not follow AO-51 in its flight over my head. It was strongest when beaming to the ground! But the antenna works as expected, if pointing some ground-based signals.

Anyway, a short youtube video with audio should show you how easy AO-51 is.

On the second attempt I actually received another "bird" sending CW telemetry on the same frequency (435.3 MHz +/- doppler), but I was unable to discover who it was, yet.

07 April 2009

WSPR: Beginner's Luck?

I had to confirm my MP3 WSPR assumptions with an on-the-air test. With the family permission I erected the antenna (base loaded horizontal monopole on the balcony), plugged the MP3 pen to the FT-817 and pressed the "Play" button at the +/- correct moment. No GPS or any real-time clock sync method was involved.

Output power was in the 0.5W ballpark, perhaps less since I was careful not to overdrive the FT817 SSB circuitry (50% ALC). FT817 uses ALC to control output power, so I need to measure it (another day, please).

On the wsprnet.org website, where WSPR spots are uploaded in real time by some kind listeners, my call appeared at 4 macro-distances: 8, 1000, 2000 and 19000 km away. 19000 km means New Zealand, The Antipodes from here.

What's Next? Either setup a WSPR Moon receiver or build an independent DSB/SSB transmitter.

One thing to mention. In this experiment I ran a 100% TX and 0% RX. I transmitted for 2 hours without breaks, except for few seconds between each sequence. This can be relaxed adding 2 minutes (02'00.00") of silence in the WSPR audio file.

Call Frequency
Drift Grid dBm
by loc km

IK1ZYW 10.140117 -18 0 JN35tc +27 0.501 OH3QN KP20tx 2121 1318

IK1ZYW 10.140117 -21 0 JN35tc +27 0.501 M0DUO IO91kw 995 618

IK1ZYW 10.140130 -15 1 JN35tc +27 0.501 IK1JNS JN35sb 8 5

IK1ZYW 10.140127 -19 0 JN35tc +27 0.501 EB1APK IN73bg 1094 680

IK1ZYW 10.140168 -26 -2 JN35tc +27 0.501 ZL3IN RE66hk 18812 11689

IK1ZYW 10.140131 -24 0 JN35tc +27 0.501 G4KYA IO93ln 1129 702

06 April 2009


Stimulated by a post on the soldersmoke blog and a direct email from Bill N2CQR about simple transmitters for WSPR, I have done some real-world tests.

My idea of a simple WSPR transmitter does not include a computer to send WSPR itself, but rather use a pre-recorded sound and play it endlessy with a MP3 pen. (But record it at the highest WAVE rate your player can reproduce, ie 44100 Hz 16 bit.)

First of all, a WSPR transmission lasts 1 minute 50+ seconds and starts at the 00 second of each even minute (x:00:00, x:02:00, x:04:00, ...). I have observed this by simply listening to WSPR program in TX-only mode.

So I need a 2 minutes long file containing my WSPR message. Problem: does my mp3 player insert a gap between the end and the begin of a file played in loop?

To find out, I recorded a single tone of 5 seconds, put it in the player and played back to the computer for a few cycles. On the computer I recorded it and then used an audio editing program to analyse it. Of course the length of the test tone is non relevant to this test, just make it long enough to be able to see it on the screen. As a result, my player introduces about 660ms (0.6") between each file. Thus the total length of my WSPR pre-recorded message has to be 2 minutes minus 0.6 seconds long.

After a short session on the wave editor program, I loaded the file in my mp3 pen, wired it to the PC soundcard and fired up WSPR in RX mode. In order to take into account human errors and reaction times, I added 1" worth of silence before the WSPR message begins. So, watching the WSPR screen and the advancing clock, I press the Play button one second before the reception begins (hh:oddminute:59).
Sit back and relax (work). It takes few runs to determine how good you were in measuring the delay. After 10 runs, 20 minutes, my WSPR looked like this one on the left (first picture).
The interesting column is DT, that shows how much "off sync" the signal is with respect to the machine clock. A DT value of 1 means your WSPR signal is 1 second late. Mine started 0.9" late and decreased constantly of a 0.1 factor each 2 minutes.

This means my WAVE file + mp3 pen delay was 0.1" too short. For curiosity I left it running for few hours until it got to -2.3 (seconds) and WSPR stopped decoding. At this point probably my WSPR signal is starting too early and WSPR doesn't catch it anymore.
Back to the audio editing I added 100ms of delay and I am watching the result while typing. Now I get an increase of 0.1" every 3-4 runs (5.0, 5.0, 5.0; 5.1, 5.1, 5.1; ...), so now I'm a bit too fast. But wait, it also decreases... I might be there!

If not, with 2-3 more iterations I should be able to get a correctly timed file.

There's another way to achieve more accuracy: generate a looooong recording, such as 1 hour or so, by concatenating many 2'00.0" sections. Your mp3 player loop delay will then occur only once in a hour, allowing for a much longer unattended operation.

One more info: for these off-the-air tests and measurements you do not need a properly GPS/WWL-locked synced machine clock. So feel free to experiment!

Now I need a simple WSPR TX, but I might try this out on the air tonight. I have it ready with 27dBm, 0.5W, my FT-817 minimum setting. I'm getting excited.

01 April 2009

Distributing 12V in the shack

All my RTX and accessories work at 12V. Since I have only one high-current PSU, I had to find a solution to distribute power amongst devices.

After asking on a forum, I did what follows.

I found a 10/16A multiple socket outlet laying around. Italian AC socket outlet has three inline holes and the 16A slot fits smoothly a banana socket. Some modification was needed, but the annoying mechanical part was already done.

After disassembling the plastic case I analyzed what was inside. On the cover there was the safety mechanism that prevents someone from inserting only one pin into the socket. It is made of the blue things and spring you see in the picture above. They come off easily. Then the surprise: current is distributed with these "rails" and the connection to the plug

Since banana plugs come with two bolts, I used the first to secure the banana to the top cover, and the second for electrical contact to the rail, as visible here:

Then I soldered all connections for a longer life without need for servicing. I needed the 30W iron and a bit of patience, but it was easy. Just be careful not to overheat and melt the plastic structure. Also the supply wire <-> rail connection has been soldered.

Now I have got 4x 12V sockets just behind the PSU for my radioes.

Apparently only Italian AC accessories are so easy to adapt for this use. Usually the cheapest model adapts best. In fact I had bought a new one for few €, but chose to sacrifice this one.