~by Peter, G3PHO

DB6NT 6cm transverter
(This article was updated and revised on 7 September 2001)

I don’t know what it was that encouraged me to email Michael Kuhne, DB6NT for one of his 5.7GHz transverter kits but I’m very glad I did! I normally do my construction work during the winter months but, after improving my 24GHz system over the 1999 Christmas period with one of Michael’s amplifiers, I received his latest catalogue. Inside was an ad for the “3rd Generation 5.7GHz Transverter”. The Sterling/Deutche Mark rate was at the very favourable rate of 3.3DM/£1 in early May, 2000, so I took the plunge and bought a 6cm kit, the MKU57G2. The kit cost just £190 ( or 598DM). It arrived within a few days of ordering and it literally took only two days to build into its tinplate box! A further day was spent making a suitable enclosure for the complete transverter (i.e. including c/o relay, metering and IC202 interface).
    On opening the parcel from Kuhne Electronic, I was immediately impressed by the high standard of presentation. There were two plastic, compartmentalised cases containing the components. Each compartment was labelled with the component value. The construction manual is in English and the circuit, pcb layout and other diagrams, including photographs are beautifully presented.  Most of the components are very small SMD types and are a very good test of one’s eyesight!



The transverter is of singleboard construction on RO4003 substrate. The DB6NT catalogue guarantees an RF output of more than 200mW. I found it easily did that and much more. A receiver noise of 1dB is claimed for the module but by the time I had the chance to check it on precision noise figure measurement equipment I had assembled a complete transverter with change over relay and sma output connector. the NF at the antenna connection measured a very creditable 1.25dB. 
    The pc board is of excellent quality, gold flashed on the ground plane side and with plated-through ground connections from the circuit side. It fits into a tinplate enclosure 33 x 55 x 150mm. SMA connectors are used for IF input and the separate antenna connections to RX and TX. Feedthroughs are used for the 12V DC input line, PTT, power monitor and the +12V output for external relay control. Everything is provided except for the external c/o relay at 5.7GHz.
    As received from DB6NT, the transverter is configured for a 144MHz IF but, with some slight component changes, it can be used with a 432MHz IF. State which you want if you order the kit.
    The actual construction presented no problems. Before the active devices were installed, the pcb was checked for soldering errors. The voltage regulators were then installed and checked for the correct output. Then the bipolar devices were fitted and voltages checked. The module was set up on my test bench (seen here to the left) where the LO was checked against my frequency counter and adjusted to 117MHz. Finally, the GaAsFETs were installed and bias levels checked. After that the tune up was very straight forward since Michael provides clear instructions with relevant voltage levels for the various test points. The filters tuned up beautifully. No one was more surprised than I was when the marker from my Adret 5401 synthesizer/diode multiplier arrangement was heard very loud and clear at T9,  bang on 5760.100MHz!
I use the IC202s for my microwave IFs. Both have been modified to give 120mW out instead of the more usual 3 watts. Since the DB6NT kit comes with an IF input attentuator for a 3W input,  I had to modify this to allow the lower input value to drive the unit.  This meant reducing the 470 ohm resistor in the PI-attenuator to 100 ohms. The fitted variable 100 ohm pot could then be adjusted for correct IF drive to the mixer. The DB6NT  transverter, as it stands, is configured to use an FT290 prime mover where +9 volts or so is present on the coax during transmit. This voltage switches a keying transistor into TX mode. I decided to leave the DB6NT intact and to make a simple two transistor keying interface for the IC202 so that,  on pressing the microphone switch,  the interface would ground the DB6NT PTT terminal, thus switching the module to TX. The IC202 has around +4.5 volts present on the coax inner on RX mode rather than the TX mode of the FT290. The interface was built into a small diecast box.

    The tinplate box housing the transverter, the IC202 interface module and the microwave coaxial change-over relay were then installed into an Eddystone diecast box (220mm x 145mm x 55mm) which had been pre-drilled and sprayed with silver hammer finish paint. Switches, input and output connectors plus a meter to monitor both the 12 volt DC input and the TX RF output where also fitted. The photographs on this page show the details. The 12 volt change-over relay came from a Teletra 23GHz TX/RX unit. It is an excellent relay and,  of course,  is to some extent wasted at this lower frequency. However it is the only 12 volt DC one I have, the others being 28 volt Transco types. To keep the DC requirements simple I therefore treated the 5.7GHz transverter to a good relay! In any case it fitted across the SMA connectors on the outside of the tin plate box just perfectly! I used two male-male couplers here plus a short length of semi rigid coax to reach the bulkhead mounted SMA output socket.

I can easily get over 300mW output from this transverter. At present I have a moderately low gain antenna system for it …. A 60cm offset dish with pyramidal feedhorn designed for 0.7 f/D. As a result, I am getting around 28dB or so gain from the antenna. Nevertheless,  I have been very pleased with the results so far, with 9 separate stations worked in two portable sessions, the best being G0HNW/P at 265km.
   I can thoroughly recommend the DB6NT 5.7GHz transverter to anyone contemplating getting going on this interesting microwave band. You can buy one ready made (and 8 watt PAs also) but you can save a lot of money and at the same time get an immense amount of pleasure by building up a kit. Similar singleboard transverter kits are available for the other microwave bands up to 10GHz.
Congratulations to all at Kuhne Electronic for a fine piece of kit!

For further details and a catalogue, contact:

Kuhne Electronic, Birkenweg 15, D95119 NAILA/Holle, Germany
Telephone:  0049 9288 8232    Fax:  0049 9288 1768
E Mail:  kuhne.db6nt@online.de

Website:  http://www.db6nt.com

In early 2001 I rehoused this transverter in a new, homemade enclosure and included a surplus 1.25 watt solid state PA. The photograph on the left shows the finished item. I have further plans to replace the PA with a 12 watt one and to add a G8ACE oven controlled crystal oscillator. This should then give me the frequency stability and accuracy I presently enjoy on 10 and 24GHz!

The photo above shows the new layout. Most of the items in the enclosure are from the original 300mW transverter but the large module at the bottom of the picture is the 1.25W PA. Fortunately this operates with a single 12 to 13 volt input and thus nicely fits in with the rest of the modules which are also +12V operated. A transmit/receive sequenced changeover module, contained in the small diecast aluminium seen here between the DB6NT transverter and the PA, was fitted as a precaution against damaging the sensitive HEMT receiver RF stages. The PA requires only a few hundred microwatts of drive at 5.7GHz so I fitted a variable 38dB connectorised attenuator between the DB6NT module and the PA input (see above the PA on its left hand side). This enabled an optimum drive level to be set up.

In 2003 I changed the PA to a surplus 12 watt amplifier that I had acquired at Microwave Update a couple of years previously. With this kind of power output to the 1.2m dish I now find I can quite regularly work the long 500km+ paths from my portable location near Sheffield to French and Dutch stations on mainland Europe.

E.I.R.P.rules !!!!