Looking for the expert on this one. Normal Tx and Rx frequency separation would either be 3 or 5 Mhz.
The question is: Can the normal 3 cavity duplexer for a GR300 be tuned for about a 2 1/2 Mhz separation in frequencys??
Ex: Rx - 460.5125
Tx - 462.9375
Obvoiusly my other option if this doesn't work is to use two different antennas
Any input or opinion would be appreciated
GR300 Duplexer Question
Moderator: Queue Moderator
The narrowest 'factory spec'd' separation I've seen for those smaller notch-filter duplexers is 3MHz. The 'standard' unit which is provided for the GR300 is spec'd for 5MHz. I've tried to tune them for 2.xx separation, with no success. Actually, I can get it to work as far as desense, but the insertion loss was somewhere around 6dB if I recall.
Todd
Todd
No trees were harmed in the posting of this message...however an extraordinarily large number of electrons were horribly inconvenienced.
Welcome to the /\/\achine.
Welcome to the /\/\achine.
My two bits worth:
You certainly can use a duplexer with this freq split, just not this one.
You will need a duplexer factory specified for your split. You will likely end up with a 4 or 6 can pass-reject duplexer, which is larger than your repeater. Do NOT waste your time attempting to tune a duplexer outside of factory specs.
The closer the frequencies, the higher cavity "Q" is required resulting in larger, more expensive cavities.
Using dual antennas is fine so long as you have them absolutely co-linear. You will need 20 or 30 foot vertical on center separation.
There are charts for this purpose. The radials on the antennas are supposed to keep the radiation off the tower, thus improving isolation.
Be very careful with the coax cables and connectors, as well as the shuields on the radio equipment.
The closer the spacing, the more critical the shielding and TX-RX isolation become. 2.5 MEG should work well.
You certainly can use a duplexer with this freq split, just not this one.
You will need a duplexer factory specified for your split. You will likely end up with a 4 or 6 can pass-reject duplexer, which is larger than your repeater. Do NOT waste your time attempting to tune a duplexer outside of factory specs.
The closer the frequencies, the higher cavity "Q" is required resulting in larger, more expensive cavities.
Using dual antennas is fine so long as you have them absolutely co-linear. You will need 20 or 30 foot vertical on center separation.
There are charts for this purpose. The radials on the antennas are supposed to keep the radiation off the tower, thus improving isolation.
Be very careful with the coax cables and connectors, as well as the shuields on the radio equipment.
The closer the spacing, the more critical the shielding and TX-RX isolation become. 2.5 MEG should work well.
Aloha, Bernie