Thursday, 31 December 2015

Lunch in Cambridge

Excellent New Year's eve lunch with some of the Cambridge hams at Horningsea today.
Lots of talk about EME and testing systems. This was quite relevant as I have been playing with MAP65 over the last few days. I want to be able to monitor the 40-50kHz of 23cm where the JT65C activity is located.

MAP65 on 2m EME

My previous attempts at getting MAP65 to work have been unsuccessful. Recently I became aware that it was possible to use the SDR-IQ on the IF output of the K3 with SDR-Radio as the interface to MAP65. My attempts to get it to work were getting nowhere until I spoke to G4IDR.  Dave talked me through setting it up. I had not spotted a small icon on the SDR-Radio screen. Once pointed out it was possible to start MAP65 and send data packets to it.

Tuning the K3 to the 144MHz beacon band it spotted and listed GB3VHF. Clicking on the display trace of GB3VHF produced a decode of the beacon.

After this I reconnected the 9 element yagi and masthead preamp and left the yagi pointed towards were the moon would rise in a few hours. 

15 minutes after moonrise I came back to see a whole load of stations listed, including RRs and 73.
Several of the stations were obviously direct terrestrial signals from the nearer continent, but at least three were by moon reflection from their DT timing on the decoded display. All in all I was pleased with this result and I'm now looking forward to connecting to my 23cm Eme system and looking at how many signals I can decode on that band/mode.

Monday, 21 December 2015

Some low noise tests

Merry Christmas,
I had intended to work on my EME dish today. However, the weather has been very wet and windy since mid morning. Consequently I decided to do some measurements on the LNA with a view to reducing my EME system noise temperature on 23cm.

After (re)reading a number of interesting articles on noise figure reduction by SM5BSZ and RW3BP I thought that I would measure the insertion loss of my LNA protection relays. These are SMA types by one of a number of manufacturers and all are surplus ( second user) SMA types with 3  in-line SMA female connectors. All are12V working.

After carefully calibrating my HP8753C network analyser ( warmed up for several hours) i found that the best I could do was 0.071dB insrtion loss from a Totsoel with 0.1dB from a Teledyne CCR 33S80
I must stress these are used relays. I have to use what I have!

The net result of using the Totsoel relay with an SMA90 bend to the feed and SMA male back to back adapter between the relay and VLNA is 0.38dB as a noise figure.
This is quite good but I believe I can improve on it using some of the techniques describd by RW3BP.
The back to back adapter can either be eliminated completely or replaced with a modified version using a piece of UT141. The probe to relay connection can be made in one piece to eliminate yet another SMA connector.
Now to try a few of thse ideas.