3cm Project

Well, 3cm is probably as high I will go. On the other hand, you never know.

I did build a DB6NT transverter around 2000, it did work however some drift and problems with output power was there. This one has not been widely used by me.

 

 

I also made a penny feed for the Lansen nose radar parabolic dish.

This type of feed has a bad reputation of efficiency. On the other hand, it is popular and simple to build.

Without adjustments with the small screws visible in the picture above the return loss was quite poor. About 13db. The tuning screws should been at the back side, my mistake.

RX was quite nice, probably because the add of the Pre-Amp visible in the first picture. This is a dual stage GaAs fet made by a company called GigaTech in Sweden. I got it from my neighbour Kenneth which also is a radio amateur (SM6DID) and was involved in GigaTech.

 

 

Time flies, and there is always new things round the corner.

I live in a urban area and noise is always a problem. HF works good sometimes, 2M has high noise levels in some directions. Now it's time to get 3cm on the roof.

New versions of the DB6NT transverter has been developed during the years, now current is G5.

I found a suitable water proof box, Hammond 1550L. And also, O-ring sealed N-connectors, the power connector is a MS-connector sealed with silicone.

 

It is recommended that the transverter is mounted on a heat sink. I made one of a piece of 3mm aluminum plate. The plate is hot glued to the box to prevent more drilling in the water proof box.

The stability of the transverter is not superb, so an OCXO is added. Some step-up and step-down modules is used for the coaxial relay, OCXO and PA.

I made a simple schematic of the Rx/Tx switching. For the PA control I use a TMR-1221 which is a small dual 5V supply. The -5V will be turned on before the 10V VDD.

 

 

The PA is built very simple, and best practice is not 100% followed, however it works. First, I tried a TMD-7185-2, but I could only have gain up to 9GHz. It was actually 0 at 10.368. This was not expected because many uses the RFMA-7185 with success on 3cm.

I found a TMD-1013 which did work, and delivers about 2W with 22db gain. I made a small brass box and soldered the MMIC. The box is mounted on a small heat-sink. Since the PA is on for short periods will this probably be ok. After a while with Tx on it becomes really hot. Before the box was closed, I added pieces of the kind of black foam IC's are usually sticked into. How much damping this does is not known by me. I just took what's in the junk box. I did not see any unstability on the SA.

 

The gain is measured with my recent added analyzer Systron-Donner 809-2.

Thank you Ronny SM7FWZ for letting it go :)

It is an old spectrum analyzer meaning measuring gain has of course some ± db accuracy.

An ADF-5355 module is used as signal source.

 

 

Complete transverter.

 

The Lansen parabolic dish with penny feed is not really water proof. I guess it can be, but I will use that one for later portable use, hopefully together with my old DB6NT transverter.

For the roof I will try an offset dish parabola. I selected a quite small (60cm) because it will be mounted together with my other antennas. If my old Ham-2 rotator will manage this will time reveal.

 

I needed a feed for the offset parabola. I made one that W1GHZ has described.

It is made from brass and a piece of WR-90. A flange mount SMA has the right pin length.

 

To be able to fixate the feeder in the parabola focal point I use an old LNA. Removed everything inside and only use the housing. The WR is centered and then hot glued in place. The front is covered by a piece of plastic from the lid of a cake can. The RL was measured to 20db @ 10.368GHz.

 

 

Here in place. If the offset parabola doesn't work good I could try with my penny feed instead. 

 

 

 

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