3cm


	3cm Equipment

My first attempt at 3cm was with a DEMI low power transverter kit. When Steve Kostro says... “the best bang for buck in 3cm kits around”, I tend to agree. The kit went together very easily, worked first time and drives the DEMI 3W PA to full output. The oscillator is the DEMI MICROLO kit that outputs 1136Mhz from a 189.3Mhz crystal. I’ve added a VE1ALQ PLL and 10Mhz ovenised reference (used Vectron oscillator) to provide a very accurate and stable signal on 3cm. A Minikits sequencer and 24v DC-DC converter to drive an SMA relay, and it’s complete.

Building modules is one thing but producing a working “system” is another. I decided to use an ex satellite TV offset fed dish, a 65cm model purchased new from an Internet retailer out of Melbourne for about $35. Working out how I’d mount the dish and feed it became an exercise in lateral thinking... come to the rescue W1GHZ, check out Paul’s on-line microwave antenna book for information on managing off-set fed dishes. I know that prime focus dishes and penny feeds have been the standard for many years in VK3 and VK5, however when I wanted a dish I didn’t have a prime focus dish of around 60cm available to me. Don’t be put off by the perceived complexity of an off-set fed dish, they’re not hard to feed and mount effectively provided you use a little ingenuity. Bonus is that you can usually pick one up for next to nothing at your local recycler.

I added a DEMI 3W PA and LNA together with an SMA relay close to the feed and connected those to the low power transverter via short lengths of LMR240. I can detect Sun noise with this system but have yet to make measurements.

While single board transverter kits are great, I thought there had to be an option that was effective and simple. What I’m working on currently is a re-hash of the original ideas of Zac Lau and Paul Wade from the early 1990’s, the idea of using building blocks to make up a transverter interests me because of simplicity, flexibility and ease of construction. Technology has moved on since Lau and Wade described their building block transverters for 3cm in the early 1990’s.

For 3 and 6cm the Hittite HMC220 is an attractive mixer package, a couple of these SMT devices easily replace the original hybrid ring and discrete diode mixers. Filters are still an issue and for my time and effort I’ll revert to a simple waveguide filter by Zac Lau based on his original article from the early 1990’s. I’ve also built a post type filter for 3cm which exhibited better performance, but at the cost of added mechanical complexity and size. The measured performance of either filter is sufficient for a 144Mhz IF system.

Gain stages are easily accommodated using MMICS such as the NLB310 from RFMD. And for low noise figure receive stages I’m using surplus gain stages off old TVRO LNB’s. The challenge however remains the oscillator chain, but there are a number of options now days that add significantly to frequency accuracy and stability. However always keep in mind the phase noise performance of multiplied PLO’s with an fo around 1Ghz, one early model PLO I tried when multiplied to 10224Mhz was a total failure because of the phase noise degredation in the receiver.

3cm Equipment