The fact that most service monitors stop at 1 GHz or 500 MHz is probably one obstacle to more use of the 1.2 GHz band. There are some pieces of test equipment becoming available at moderate prices, so that may change.
It sounds like your immediate interest is receiver testing. Some 2 GHz signal generators are starting to show up for less than $1K, so you may want to start saving. In the meatime, perhaps you could try building an upconverter. Something similar to the transverters the weak signal folks use to get on the higher bands but using your service monitor as an IF rather than using a transceiver as an IF. Perhaps some parts or kits from Down East Microwave would work for you. Alternatively, for receiver testing, you might be able to feed your service monitor's generator output into a simple mixer along with a suitable LO [local oscillator]. You should be able to find a mixer from Lorch or Mini-Circuits on the used market for a few bucks. Research mixers in the Mini-Circuits RF/IF Designers Handbook or get the application notes from their web site. You will find that you will need a LO that generates somewhere from 0dBm to +10 dBm or more. Where to get that cheap, easy, and quick? How about using an 800 Motorola Maxtrac? One of those with the 5- pin board and no T/A VCO that no one wants can be had for a few bucks. Pull the PA off it and you will find a little coax that feeds the PA. The PA drive is around +17 dBm. Close enough that you should be able to get the correct mixer level by simple adjustment of the Maxtrac bufer amp or by inserting an attenuator. Just follow the instructions on the repeater-builder site to blank the radio and convert itto conventional. Program in one receive frequency. [Pick what you want for your LO by subtracting the radio's 45.1 IF from what you program in] Make a hardware mod so the TX buffer is live all the time so you have RF out the TX to PA coax. Hook that to your mixer LO port, your service monitor generator to the mixer RF port and the mixer IF port will be your new RF out. Say you program the radio to receive 865.1000. Minus the 45.1 IF, your LO will be at 820.000. Subtract that from your receiver's frequency and you have the frequency for your service monitor generator. Remember the level of your generator will need to be set higher to offset the mixer conversion loss. Ideally, get with a friend who has a spectrum analyzer while you work on the project so you are sure you get the levels right and know your exact offset for a calibrated output. --------------------------------------------------------------------- -- --- In [email protected], David Struebel <[EMAIL PROTECTED]> wrote: "... I have a 1.2 GHz repeater, but no service monitor or signal generator for these frequencies. My service monitor, a Singer- Gertsch only goes up to 499.995 Mhz. ..."
