Tuesday, 8 June 2021

Single-Yagi EME


After being absent from 2m EME (moonbounce) for the past couple of years, I decided to spark-up again this spring to see if my simple system was still up to the task.

Pretty much every month, during the moon’s sweep through its northern declination, I get several days with moonrises right out in front of the house overlooking Georgia Strait. This is the large body of saltwater separating the British Columbian mainland (and the rest of North America) from Vancouver Island to my west.

Having an ‘over the ocean’ moonrise offers several advantages for me as it pretty well guarantees an extra 6db minimum of system gain (both on transmit and receive modes) and provides a noise-free environment for the antenna to look into.

Because of this advantage I’ve been able to get away with a very minimal system consisting of a single 9el Yagi and a small FM ‘brick’ amplifier which yields around 120W of output. The antenna is tower-mounted at 60’ and controlled in azimuth only. Without being able to track the moon as it rises, the Yagi is broad enough to give me about 2 hours of moon-time on each session before I start to lose signals. With most EME stations using four or more Yagis and high power, most of the heavy-lifting on my two-way work is being done by the other station. With the extra sea-gain here, my single 9el Yagi performs more like an array of four similar Yagis.

There always seems to be new stations to work whenever I get on the band and this spring was no exception. All told, I had 20 contacts, with 12 being new 'initials', bringing my total initials count to 130. The remaining 8 contacts were with stations I have worked previously. I was also able to add 2 new states, New Hampshire and Wisconsin, bringing my 2m WAS total to 30.

Conditions were poor to average, with one day in particular being excellent, when at one point I had a pileup of three callers!

Most of the stations contacted are always surprised to learn of my small system and comment that my station is the smallest one they have worked. I have worked a couple of two-Yagi stations over the years with one of them being worked several times.

Here are the cards that have arrived so far for this spring’s session:

If you haven’t given single-Yagi EME a try I would encourage you to test it out as you might be surprised at your results. Even without the added sea-gain, many of my contacts were loud enough to be easily workable with 6db less gain ... and there are dozens of big capable stations out there just waiting for new initials!


Michael said...

It is amazing. In 1964 they got permission to use Arecibo for moonbounce, and Wayne Green said it sounded like 20M. The dish had so much gain that felatively simple stations could get through.

In 1972 it still seemed like you needed a bit of oomph, but maybe it was showing signs of improvement. There were more stations with big antennas, so it wasn't like the early days, when both ends needed great antenna and amp.

In the late sixties, Ray Naughton in Australia did well, despite the rules limiting him to I think 150W. But he lived on the outback, lots of room. So he built rhombics, long and hanging off surplus telephone poles. He did fine, except he couldn't aim them (well he couod change the angle a bit with rope pulleys). So his moonbounce activity was a few days each month, when the rhombics could see the moon.

Vasily Ivanenko said...

Congrats. Pure inspiration Steve

PBealo said...

You are tempting me! What mode(s) do you use?

Steve McDonald said...

Tnx comments guys...Peter, give it a shot. Choose your times to coincide with closest approach and days of maximum EU activity. Check out the eme chatter on Ping Jockey and you can get a feel for how things work. The mode is JT65B. Good luck!

ATMBob said...

I haven't tried JT65B but use FT8 almost exclusively from 6m down to 80. Does JT65B give you an indication of received SNR?

My question centers on if you can you see if the extra 6dB you get from the reflection off the water means contact vs. no contact. Even with the other guys doing the "heavy lifting."

I'm trying to prepare for 6m EME, but an array of 4 long yagis isn't possible on my small suburban lot and the nearest saltwater is a mile away. I might get "a couple" of dB help from the relatively flat yards within the first few wavelengths, but certainly not what saltwater would give. A single long yagi might be possible if it's to point toward moonrise or moonset.

It seems the best I can do is right on the edge of possibly working.

I'm just about as far SE as one can get and still be in the US. I'd like to get from 48 states to WAS on 6m and (of course) need HI and AK. It's not looking like EME is feasible.


PBealo said...

I'm in Eastern NH (FN42) and with my modest 5el 6m beam and 100W have worked California several times on FT8. You may not need EME for the lower 48 states.

ATMBob said...

Thanks, Peter, but I already have the lower 48 states confirmed on 6. It's the farthest two that I've been unable to hear in over 10 years of trying.

Steve McDonald said...

Bob, JT65B gives you an SNR value for each decode, basically the same as all of the digital modes. I'm evaluating my 6db minimum gain based on the information given in the one of the RSGB Handbooks which states this value as a minimum. I honestly believe it is that, perhaps a little more as I see better performance than expected on any band I am set up to operate. I don't think I could have had this same success on 2m EME without the added gain.
I have noticed on 2m EME that often signals will rise out of the noise in mid transmission and become audible...usually it is around -16db for me. When they hit that point I can hear them by ear.Many of the signals that I work are much weaker than this, up to -27db. Removing my 6db of sea gain still leaves a lot of guys that I could work without the ocean's help.

If you watch the ON4KST 6m Region 2 chat you can follow the prop every minute of the day. There are several openings to JA and W4 each summer on some form of enhanced E and often KL7 is at one of the enroute hop zones and KL7 is worked from W4. It is a challenge for sure but the same happens to KH6 once in a rare while.
To grab KH6 and KL7 on 6m EME will require a big station on the other end and I'm not sure there is one in KH6 ...maybe KH7Y. KL7UW I believe is EME capable on 6 so you may want to talk with him.
If Cycle 25 turns out to be a decent cycle, you should easily work these two sates in the winter of 2023 if all else fails :-)

Scott the Dad said...

Steve - what radio do you use, and is frequency stability a huge concern with JT65?

Also, do you use a preamp anywhere in your system? How many dB?

Steve McDonald said...

Scott - I use an (old now) Icom 821-H without the 'high-stability' option. It's stability is fine but anything much older might be a problem. I always let it warm for at least an hour and I see no drift.

My little FM/SSB brick amplifier has a built-in GasFET preamp.It would be more effective up at the antenna but there is also benefit to having it in the shack as it makes switching and protection easier.