Messing about with Microwaves – A 3.4 Ghz Transverter from a surplus Subscriber Transciever…

 

 

Around 18 months ago I had the foresight to obtain 3 surplus 3.5 Ghz subscriber panels made available from the Geelong Amateur Radio Club. The information is still up on their website here.

These panels sat unused in my shed until a few weekends ago when I FINALLY got around to doing something with them, so out they came for a session with the screw driver…I wasted no time in undoing the 4 million screws that hold the back cover for a look inside…

They are nicely made, and contain a full duplex TX RX set up with an intergral 18dBi panel antenna that did wireless internet on 3.5 Ghz.

Some clever chaps at the GARC have devised a way to make these a goer on our 3.4Ghz ham band. The main activity in Australia has shifted down to 3398 MHz SSB from the old 3400MHz. This is due to a recent shift in the frequency allocation in Australia for this band. The panels work fine on either frequency. As modified, the panels run an IF of 442Mhz for 3398 MHz

So far, I have started to modify one of the panels according to the instructions, including fitting a Minikits 2.6Ghz Relay kit for TX/RX change over. I was lucky enough to have the 12 V version of this kit (which has since been discontinued due to the relay becoming obsolete) spare in my junk box. This was duly constructed and fitted to the original board. I unsoldered the existing MCX socket for the antenna connection from the oringinal board and soldered it to the output of the relay board. The original Panel antenna now plugs in here. The 5V version is still available however. (Just use a 180ohm dropping resistor for 12 V)

I used a blowtorch to gently heat the covers that needed to be removed, once they were hot enough they came off quite easily. The far left cover was removed by mistake!

I’m currently waiting on the switcher board PCB to arrive, so I can continue with the conversion. The hope is to have this ready for the next VHF-UHF Summer Field Day contest on the 14th and 15th of January 2017…this will be my 1st Field day for several years, after losing interest in Amateur Radio for a while…I’m back!!!

Update 31/12/2016: The Switcher board finally arrived!

I wasted little time in assembling and testing it, and mounting to the main pcb, and finishing off the Transverter conversion…

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The only real snag I had was the modification of the TX mute section of the panel, the instructions called for moving a resistor to another location, but after thinking I’d done it, initial tests showed no additional current was being drawn on TX. It was soon apparent the tiny 1M ohm smd resistor wasn’t soldered properly and repeated attempts to reposition it and try again failed dismally – it’s just too small!  This prevented the unit from going into transmit. I ended up putting in a conventional 1M resistor to make it functional. It worked fine after this.

 

The unit is now drawing approx. 800ma on transmit, in agreement with the documentation. Some of the soldering required to mod the panel is certainly a challenge, as you’re dealing with smd smaller than 0805. These components are TINY!!! You need to be careful…

Here are another few snaps of the progress. The unit is now complete, and is switching to TX as it should when connected to my FT817. The next step is to adjust the receiver…

As I have limited test equipment, I’ll set up a 3.4Ghz source and tickle up both RX filters using the onboard signal beeper as a guide…

Update 6/1/17…It’s alive!

Yesterday I travelled down to Adelaide to see Tim, VK5ZT, as he kindly offered to help align the receiver and check the panel TX.

Tim has quite a collection of RF test equipment and he soon had the panel hearing very well. I had attempted to try this myself but the instructions for adjusting the filters in the documentation are a bit “out there”. Far better to leave the filters screws as they are an adjust them from there as a starting point. Tim also recommended the two stubs on the filters be removed also, so they were duly unsoldered. The panel was able to easily hear the 3.4Ghz Elizabeth Radio Club beacon reflected from the side of Tims house through the shed/shack door at around S8! We then netted the panels’onboard  10Mhz oscillator to frequency as well. We checked TX and established the panel has a clean and healthy output on the spec-an. Job done!

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Here you can see the panel listening to the 68th harmonic of my 50mhz oscillator connected to a  2-11Ghz log periodic PCB antenna…( at the bottom of the image, pointing at the panel antenna)

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Back cover on and ready for a run in the Summer Field Day contest next weekend!

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