Sunday, October 14, 2012

Uh-Oh....I May Have To Go To "Plan C"

WELL.....got everything assembled and apparently working, until I tried to transmit. I'm having a horrible case of receiver "desense", which basically means that my local transmit signal is hammering my own receiver. This results in the complete overwhelming of the receiver, and I can't hear my signal coming back from the satellite. I can hear other users just fine, but when I transmit, all I hear is a distorted version of my own uplink.

I had this problem when I first got started many years ago, and followed the hard won wisdom of all those who've gone before me. Namely, ADD SOME FILTERS.

I have a filter on the UHF side which only passes signals from about 380 MHz to 500 Mhz, and another one on the VHF side which only passes signals from 144 MHz to 148 Mhz. These are basically used to keep any 145 MHz fundamental from getting into the UHF side, and to keep any 3rd harmonic from the VHF side from getting out of the transmitter.

The UHF filter is ahead of the preamp, which has it's own helical filters inside, and the VHF filter is connected directly to the output of the transmitter.

Up until now, it's worked "As Advertised", and I haven't had this problem since I started using them.

SO......I either have something connected wrong, or the antenna I'm using isn't real happy with the way the coax runs to it. The antenna I'm trying to use (and it's worked fine before) has the VHF and UHF elements on the same boom, mounted at 90* relative to each other to minimize and cross-coupling. Sometimes the way you run the coax can have unpleasant results, but I don't have the time to troubleshoot a rather arcane problem like that.

Tomorrow I'm going to tip the tower back over, and reinstall the two separate antennas I use for Field Day, on the long cross-boom, check ALL the cabling again, and give it another go.

I *know* that set up works, and I've been using it for several years now, both at Field Day, and here at home.

The big problem with transporting all this stuff down to the IOWA is I'd have to rent a trailer. Fortunately one of the guys who's helping with the event has a full-size pick-up, and he'll swing by here Friday morning to load it up and take it down there.

1 comment:

  1. Sounds like you can't win for losing ... but I have no fear. You'll figure it out!

    ReplyDelete

Keep it civil, please....