Tuesday, December 25, 2012

5.7 GHz poor guy transverter

Not so many simple transverters for 6cm band seen up to now. So here is one, really simple and working, with minimum parts required and poor guy like me did find all the parts within the pile of microwave "LEGO bricks".

The architecture is traditional and straightforward, no bells and whistles in this design. The core of the transverter is the mixer. Simple as it can be, SKY-60 double balanced mixer working up to 6GHz with affordable price, new through the e-bay purchase. Drive on the IF port 0dBm @ 432MHz, +7dBm @ 5328MHz for the LO port. On the output RF port we have LO, LO+432MHz and LO-432MHz signal present. To get rid of the unwanted signals the mixer is followed by the filter. Here we can use many types of filters but the pipe cap was a simple and cheap solution, can be tuned easily even with no special measuring equipment. Tune to peak method will give good results. Of course the frequency is 5760MHz. This filter will be used both , for RX and TX operation. PIN diodes, RF switch, relay, resistor splitter or Wilkinson divider. Well, the Wilkinson divider was appropriate and simple enough for this approach. More over, no switching required for RX/TX operation. I made mine from the old 1.8GHz cellular equipment easily cutting out the peace of the PCB with the printed divider. Simple calculation, sharp x-act knife and the divider legs were modified to L/4 @ 5.760MHz. This way I end up with two ports, one for the RX and the other for the TX side of the transverter. For the RX front end i choose not the best, but cheap and simple MMIC block with the MGA-86563 declared to work up to 6GHz with not so bad performance. The MMIC was biased for the maximum gain with 8V power supply. On the transmitting side there is also a MMIC block, simple Sirenza SNA-586 good up to 6GHz biased for the maximum gain with 8V power supply. 


So this is it, a simple transverter, of course with the limited performance but good for the quick qso with the neighbor station or somebody on the hill within the line of sight. To operate this transverter we need some kind of local oscillator and a simple electronics handling the power and antenna switching. Crystal oscillator with the chain of multipliers can give us maybe better phase noise but better stability and more flexibility in choosing the IF insure the synthesizer built fir microwave frequencies. I choose the VK3XDK Si-4133 synthesizer version with the 16 programmable frequencies. The synthesizer is locked to high quality 10MHz double oven oscillator granting excellent stability and lower phase noise comparing to the cheap 10MHz canned oscillators. I prefer to use the 70cm IF so the LO was programmed to 1776MHz. The 13dBm output was attenuated with the 7db attenuator to safely drive the 3x multiplier box producing some 15dBm of the signal @ 5328MHz. Again 7db attenuator between the multiplier and mixer to bring the signal to the required mixer level. At the same time the mixer was very happy to "see" the 50 ohms impedance at any port. For this experiment i choose the IF 432MHz, but much better will be 434 or higher. Not more than 0dBm is required on the mixer IF port, so the 27dBm (500mW) signal from the FT-817d was reduced with the 26db attenuator at the sequencer board. Sequencer is also switching the power for the MMICs in the transverter as well as the power for the coaxial relay at the output. RF sensing and PTT ports insuring high protection. If the coaxial relay or RF electronic switch is not available we can use two separate antennas for the RX and TX. With this arrangement the setup is ready for the smoke test and initial qso testing. The output power is low, not reaching not even 1mW and the conversion gain is also poor just a few db so some extra amplification is required for serious work. 


Good LNA will lower the noise figure and improve the conversion gain and on the other side a few MMICs on the TX side will give us pleasure to work some distant stations. Just for the test I add another SNA-586 on the TX side bringing the signal up to the 3dBm. Not much, but at the same time I add another pipe cap filter between the MMIC blocks to reach the cleaner signal at the output. Result can be seen at the video. The same approach can be used to build the transverter for the other microwave bands, so no excuse for the low activity at the microwave bands. 

So "Use them or lose them"


4 comments:

  1. Hey Adam, nice lash up! What is your Transverter controller board?

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  2. It is a simple PTT (ground) control plus RF sensing control with IF attnuator switching and DC power switching part. A kind of small sequencer, very primitive one.

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