DownConverters and Preamps for Dishes

AO-40 Receive

The most frequently used system is a surplus MDS crystal controlled downconverter modified to receive the 2401.3 MHz signal on 145.3 MHz.. Many hams have tried converting on of these surplus MDS downconverters themseleves, and those on the air are the successful ones. But unless you are a technical giant, get one converted and tested for you by a technical giant! Then, try your hand at improving.

The classic MDS downconverter is the Drake 2880, but sources for this unit seem to have dried up.

2401 MHz Downconverter Sources

The 2401 MHz downcoverter pictured at the right is a "California Amplifier" #31881, a converted MDS unit available through WJ6T. Bob converts these units and adds a crystal for output on 2M for $55 pp. After Bob works his magic, they work quite well..

Bob Seydler K5GNA (281) 852-0252 k5gna@aol.com has an starter system, called the "Complete System" for $175. It consists of a 3' barbecue grill dish, a converted and tested AIDC 3733 down converter, 2M xtal, Murata filter, F to BNC adapter, power supply and 75' of cable. Such a deal. Another downconverter from K5GNA is an AIDC 3731. This is a new version with an excellent front end comb filter that has a lower noise figure. A select version modified for 2M witha .89 or less NF is sold by Bob for $115. I used one of these, further modified for 12 VDC operation on my 10' dish's dual band patch as shown on the right.

New 2401 MHz downconverters are available from SSB Electronics and Down East Microwave. The SSB UEK-3000 is the top of the line in AO-40 downconverters, and is priced accordingly at $475. The DEMI downconverter is a bit more reasonable. Often the DEMI preamp for 2400 MHz is used ahead of the surplus MDS downconverters. Unfortunately these great downconverters have a serious front end overload problem when used in proximity with the uplink antenna on 435 MHz or 1269 MHz. The AIDC 3731 has a comb filter in its front end that eliminates all the overload and desensing making full duplex operation possible. I use nothing but AIDC 3731s with my dual band and tri band patch feeds.

A common woopsie is transmitting into your down converter. This will pooff your downconverter's output stage. I recently did this to my PrimeStar's UEK-3000 when I tried to use 2M FM into an unmarked piece of coax, thinking it went to my 22 el 2M yagi. Fortunately the output stage uses a cheap little MAR-3. I couldn't find any MAR-3s in the junque box, so a MAR-4 worked just as well. Wheh!