[Moon-Net] DISH SIZE FOR 1296

Courtney Duncan courtney.duncan.n5bf at gmail.com
Mon Nov 21 16:43:21 CET 2016

Hi Serge,

I put up a 3 m. dish because it is the size K1JT recommended in his excellent ARRL Handbook section on EME.  (In my 2014 Handbook, this is not in the printed pages, but in the included CD, which I printed out!)  In Table 9 he lists “Typical Antenna and Power Requirements for CW EME” in which for 1296 he says 3 m. and 160W.

3 m. is the largest antenna I could assemble and put up myself (i.e., without a crane or other special equipment or a dozen friends and a case of beer) and the smallest with which I could dependably see (and occasionally even hear) and measure my own echoes.  My requirement is to be able to see my own echoes.  Then, I will be able to work any other station that can hear their own echoes.  I did not want to be limited to being able to work only other stations that are larger and I did not want to be limited to performance tests that I couldn’t do self-contained with my own station (e.g., echoes).

In my limited experience (over the last three months of being on 1296 EME, I’ve completed QSOs with 35 different stations on JT modes and 14 on CW), I can dependably work, in JT modes, stations of my own size (equipment as indicated, for example, on HB9Q listings), can easily work larger stations, and can often, and perhaps with some difficulty, work stations down to 2.3 m with at least 200-300 W.  (I haven’t yet completed a QSO with any station on yagis.)

On CW, another station of my own size (3 m., 300 W.) is the minimum and it’s better if the other guy is > 3 m. and 600 or 800 or 1500 W.

This agrees with my echoes comment.  I see and measure JT echoes readily.  I can audibly hear my own echoes only under the best conditions.

So I would say, if you want to work 1296 EME CW with anyone but the big guys, you need to be at least 3 m.

My EME dish is prime focus.  In my local 10 GHz community there is great discussion about the difference between prime focus and offset feed.  My own opinion is that there is more discussion on this topic than actual difference.  I run offset feed on 10 GHz tropo and don’t really see that much difference in performance compared to other prime focus stations of similar size and power.

I have not yet tried different feeds and chokes on EME so I can’t say how worried I am about shadowing loss (I’m not worried right now with my choke-less feed but I do plan optimization experiments in the near future) but I can say two things:

1.  In the contacts I’ve made so far where I know what the equipment is on the other side, I’ve only worked one offset dish, most of the stations appear to be are prime focus.

2.  I align my system by pointing at the sun or moon and observing the shadow of the feed on the center of the dish.  An ad hoc alignment process like this is much harder on an offset system.

73 and good luck!  Courtney, N5BF

At 07:25 AM 11/20/2016, serge wrote:
> For some of you that actually are operating on 1296 could tell me 
> the minimum size for a prime focus dish or offset dish to operate on 
> CW? after you have worked the big guys?? Would anything less than 10 
> FT/3M be worst looking at or not??.
> Thank you
> Serge VE1KG
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