The star of the whole show is the 2.4m folding dish from Sub-Lunar Systems. Without this dish and the feeds from Paul, W2HRO, I would not have even tried to do 1296 or 902 MHz EME. KB7Q wrote this in October, 2020, “The key part of the project – the small W2HRO folding dish antenna with patch feed…” KA6U is using Paul’s dish creation for his 1296 roving.
The feed configured for circular polarization is deceptively simple and even easier to put on the air. As shipped, the 90 degree hybrid is labeled for TX and RX.
Here is a comparison photo showing the size difference of the 902 feed versus the 1296 feed as configured for NX9O Rover.
Paul’s feeds are based on patch feeds from SM6PGP. I found a detailed description in a Swedish EME-meeting May 2013 paper, “Circularly Polarized Patch Feed for 1296 MHz”, published by SM6FHZ and SM6PGP. Toward the end of the presentation there is a suggestion of a good way to setup the feed for circular polarization.
While this method of connecting the feed for circular polarization is quite comprehensive, for field use, it is way too complex. It is much simpler to use split transmit and receive lines, put the LNA at the feed, and use a small RF relay to protect the LNA during transmit. I tried to source suitable 12VDC SMA relays for my feeds, but the relays I was shipped turned out to be latching and not failsafe. Getting failsafe versions of these SMA relays is much easier at 24-28VDC. That is what I ended up doing. I rewired the control cable to the feed to add a pair of lines for 24VDC relay control to go along with the 12VDC LNA power. These two lines are enabled when I turn on the sequencer, and are dropped by the sequencer when going into transmit. At some point I’ll add a block diagram to this page to show exactly how I did it.
Purists will point out that maybe I did it wrong. The decision to provide more protection to the LNA’s was deliberate. I might have a minor amount of discontinuity to my circular polarity and/or impedance mismatch during transmit by having the RX port effectively unterminated. It is a conscious decision. On 1296 with up to 500w I have more than enough power to make up for the discontinuity. On 902 it seems to be relatively circular based on the few reports I have been given so far with less than 200w. I am hoping to be able to improve my transmit output level during this next year on 902.
The other choice that some may quibble about is that of circular polarization instead of linear with the ability to switch between horizontal and vertical. I agree that would be more compatible with most of the existing stations on 902. As a newcomer to 902, I am fighting the history. I have seen how easy it is to concentrate on the rest of the factors and not have to even think about faraday or polarization mismatch when using circular polarization on 1296. The fewer things that need my attention when I try to activate a new location, the better. The 902 and 1296 feeds are completely plug compatible in my system.
This summer I expect to add 2304 MHz. My new feed has already arrived from W2HRO to my home in Georgia. If all goes well with amplifier retuning, I will have 140w or more. It should be a lot of fun. I hope to put on many states, but I probably will not ever reach the level of dedication that KA6U has shown in making his activations. I hope to work all of you many times.