A Bit of MIcrowave.

A while ago I went to a rally and got myself  power amp for 1296MHz.

The amp is built with 4 10-15W power modules and has a built-in linear power supply. It is quite heavy, so it is not suitable for portable use or outdoor mounting. The nominal output is about 50W.

The amplifier has no T/R switch relays built-in, so I will have to make myself an external relay system. As I am using a preamplifier I will have to use a sequencer as well, as I would not like to destroy the preamp.

Yes, I have already destroyed one preamp for 1296, not by transmitting reverse into it, but likely for one of 2 reasons. Either a lightning strike nearby, or (more likely) transmitting up to 100W on 2m from an antenna a few meters away. The antenna for 1296 was a 3 band antenna for 144/432/1296MHs, with no 1296MHz filter. 

I noticed it one day, when the preamplifier was switched in, the noise increased, but the signal from the local beacon went down into the noise. Bypassing the preamp reception had a much better signal to noise ratio. I can replace the preamp for a next try, and I intend to mount a triplexer (144/432/1296), so the 2m and 70cm signals into the 1296MHz preamp will be attenuated considerrably. More to do, once again, and I will need to call for assistance to get the system up and down.

I am still thinking of a portable system for 1296MHz, so I can operate from hilltops or other suitable places. That is a bit further into the future.

Now for some 10GHz news.

I found an old transverter, built with much assistance from a friend. It has been dormant for several years, and I have retrieved it from my storage. A mounting plate for a tripod is included, so the system is made for portable use.

This is a quite old construction built with modified modules from Qualcomm, and should privide about 500mW of power. 

The system was "born" with a home made waveguide transition and a 48cm dish. During transport the dish has been bent out of shape, so it will need some repair.

I intend to use a smaller horn antenna (15dBi gain) with WR90/WG16 waveguide  for the first experiments.

The wavequide was using a non standard flange, so I deeded to use a modified waveguide extension, modifying the flange used at the transverter end, and standard at the horn antenna. That modification is done.

I also got myself an old FT290R (1) transceiver that should be suitable for controlling the transverter. The T/R switching uses a DC (bias) voltage (>5V) for switching into TX mode, and the FT290 should provide that voltage to the transverter through the antenna cable. Unfortunately the voltage drops below that threshold when the transverter is connected (only 2V). Not good, so a modification or repair of the FT290 is needed, or maybe a modification of the sensing circuit in the transverter.

The receive side appears to function properly, there is a sufficient increase of noise in the FT290 RX when the transverter is switched on.

When the TX part is activated, however, there appears to be a quite low output from the transverter, the needle of the built-in power meter hardly moves, but it does move. More to investigate.

There is a possibility that the negative gate voltage for the PA stage has dropped out ... Oops, new PA module needed. It's not a disaster if this is the case, I do have another PA module.

We shall see when I get more tests done, and when I can get it up and running. Hopefully before winter.