Thursday, 8 November 2018

Moonbounce and a bit of tropo

First of all, there was a nice little 144MHz tropo opening here on 5 November. There was also a bit of aurora about but I heard none of it.
144MHz contacts at GM4FVM on 5 November 2018
Not bad at all. It took all day but I worked 12 squares, with DXCCs including GM, G, F, DL and OZ. DK8WK is 1078km so that was not bad either. A new square was GM6VXB who this time was in the wet square IO98. It helps that Martin works off shore and occasionally operates from the strangest parts of the North Sea.

Worth mentioning is that the barometric pressure was not high. What the weather was doing was looking like the pressure was high when it wasn't - it was about 1012 mb (I should be using hectopascals I guess) but pretending to be 1030 with a lovely mild, still, clear day here with no wind and plenty of sunshine. That is one in the eye for the weathermen at the RSGB propagation predictions department. They didn't see that coming (well, neither did I).  

I am not entirely sure how to put all this into context with my contact last week with NC1I on 70cms Earth-Moon-Earth. Jan OZ9QV commented "I am looking forward to hearing more about 70cm EME from you." That is a fair enough comment but I am not sure. I know that many others have caught the EME bug and gone 100% for the Moon. On the other hand I was back on tropo duty the next week.

An email has flooded in from Frank, NC1I, who read this blog and kindly commented. He also sent me a screenshot of my QSO
GM4FVM as seen from NC1I on 432MHz moonbounce.
Click the image to enlarge, as per.

Frank says that I was -24dB on the first day and -26 on the second day. As I was a new station for him Frank confirmed that I was not in his database. Thus I was heard without the benefit of deep search.

It was great to hear from him and also good to see my signal on his waterfall.

He adds "My station uses (48) 15 element K1FO rear-mount yagis. I have mechanical polarity rotation however if I remember correctly at the time of both of our QSO’s I was receiving and transmitting horizontal. Power at the feed is around 1100-1200 watts. I have a cavity preamp that measure around .16 dB nf mounted at the feed. This system has been in use almost continuously since 1994! I live in a rural area and have about 5-acres of property but still there are houses less than 100 meters from my array so I do have noise/interference, especially near the horizon."

The difference is colossal - he has 48 times 15 elements, and I have one 12 element yagi. He has 1100 to 1200 Watts at the feed but I have less than 95 Watts. The key factor of course is his preamp which allows him to hear my weak signal.

I think Super Stations and weekend dabblers are like the poacher and the gamekeeper - we need each other. If we didn't have poachers (that's me by the way, a sort of blow-in who makes the minimum of effort and liberates the salmon) we wouldn't need gamekeepers, but then again, if we didn't have gamekeepers there would not be so much game to attract the poachers. So we live off each other. The little stations benefit from the investment of the big stations, but the big stations get the squares and the nice DX on a regular basis. It seems like a happy balance, except perhaps that there are not enough of either of us, at least on 70cms.

If I wasn't for Frank and his carefully engineered station I could never have done it.

Frank also confirmed what Jan suggested by confirming that even smaller stations are possibilities for improbable DX ... " The smallest station I have ever worked on 432 EME is a 3-element yagi (that’s not a typo it was a three element yagi) and 60-watts so it doesn’t take much. Single yagis with 12+ elements and 50 watts are pretty easy for me to work. My array gain is 31+ dBD."

Whilst my contact with Frank can hardly be described as a great surprise - I did think it was possible if unlikely and gave it a go - it has certainly surprised lots of other people. Several locals have been reeling in amazement. For those who think that moonbounce is something for others comes the dawning realisation that they could do it if they tried.

At the other end of the scale, John, GI7UGV, is one who does try and he got in touch. He was listening the same day as me and he heard DL7APV (I didn't!). John has a better receiver and antenna set-up than I have but he was not in a position to reply. John is known to me as a satellite and amateur television operator but it seems that he has been bitten by the moon bug too. It is a very inviting area to explore. As John said "It actually worked, shouldn't be surprising as was told it would work but actually seeing and hearing the signal ever so faintly in the speaker finally confirms it :)" That captures the excitement of the moment better than I could.

Finally, another amateur asked some very detailed questions about EME and I will post below my reply to him. Each point is open to debate by you all, but I was trying to dispel a few myths.
1) I am just a beginner. That has its merits, because I do not have complex gear or big antennas.

2) There is a "centre of activity" on 144.120 which some people use as a calling channel. Otherwise everybody is spaced out a 1kHz intervals between about 144.105 and 144.145

3) I use a combination of these sites to find out who is on ...
Basically I look to see who is calling CQ and then if they are strong with me I might call them. You can tell the Super Stations as they give their antennas and power on the chat room, 2x12XY/1.5K is two 12 element crossed yagis and 1.5 kilowatts. By comparison mine would be 7H/300 for a seven element horizontal yagi and 300W which is small. However, the gain figures add together and if I can hear someone running, say, 600W, then they should hear me 3dB lower, or 6dB lower if I was running 150W. Most of the time I run 200W on 2m. Generally they can hear down to about -26dB.

4) There is far more activity at the weekends. HB9Q is on 2m most weekends and they use a large dish and can work stations down to 50W and simple antennas. Most stations who take part in UKAC contests could work HB9Q at moonrise or moonset.

5) They don't count countries or squares so much as initial QSOs. After all, once you go via them moon it doesn't matter where in the world the station is in terms of distance. I don't routinely post on the chat room as I don't often call CQ. Sometimes I post a thank you to somebody I have worked which is also a confirmation. If I do that I get besieged by dozens of stations on the chatroom who want skeds.

6) I can get to within 1 degree of accuracy which is far better than I need with my antenna. However, that is once I have got it pointed at the moon. Because my mast is in two  telescoping sections there is play between them and I probably do not get better than +- 2 degrees to begin with. This does not seem to matter.

7) Most people use JT65B. You can use CW and I can hear HB9Q's CW ident perfectly clearly. The WSJT-X software can show all the directional and elevation data if you select "astronomical data". You need to tweak the WSJT-X settings a bit. This is to largely get round the error correction which would otherwise stop you decoding a lot of it.

8) One QSO per day is my practical limit. I have about an hour at moonset or moonrise. QSOs take about 8 minutes and it is all peace and calm compared with meteor scatter.

9) There are so many variables that conditions change over the month. The moon distance changes about 10%, for instance. Then there is Faraday rotation, polarisation differences caused by the curvature of the Earth and the range of the station you are working ... sometimes a week or more would go by when I would hear nothing.

10) Elevation isn't everything. Several of the "big" EME operators in England have no elevation but they do have, say, 2 x 9 ele Tonnas. You soon get to know that your antenna has lobes in the vertical axis which you can use as the moon rises or falls in the sky. With a single antenna and a hundred watts most UKAC stations would be in with a good chance, though a mast-head preamp is the only thing you would want to add if your coax run is over 20m.

Just doing it once is most of the fun. Simply listening and learning is fascinating to me. Nothing about it really makes me think I would want to have a Super Station and high power. I have worked stations on 2m and 70cms, but only heard one station on 6m. So far!

P.S. I find this site handy as once you have told it where you live you can see ahead as to when moonrise and moonset will fall, what the angle will be both horizontal and vertical, and the moon distance...
It is well worth reading GM4JJJ's comments to my last posting.

Many of the generalist "VHF" books are not very helpful. In my view, they tend to make the whole thing look difficult and expensive. There will always be a photo of some enormous Goonhilly type antenna and some QSL cards from an operator who spent a million quid on gear and who lives in a stately home with enough land to put up said antenna (bitter ... who me?). Whatever happened to the concept that this hobby progressed by taking many small steps, each adding a quantum of improvement, and each of us developing skills and knowledge along the way?

As so often, I disagree. I disagree that this needs to be seen as difficult. With folks like Frank, NC1I, around, us ordinary types have a chance of a really memorable EME QSO. I thank him for that.

We need a few gents in this hobby. Luckily there are still a couple of us about.




P.S. Just in case you think I am going cold on EME, I have thought about a separate (small) antenna system with elevation ...

1 comment:

  1. A question on the tropo, was it traditional SSB/CW or the dreaded FT8? ;-)