One of the easy tests I use to check for transmit to listening antenna
coupling is to simply connect a wattmeter to the listening antenna .. Then I
transmit with up to 1500 watts . If you get any deflection on most
wattmeters it is too much coupling to maintain the directional pattern of
most antennas... With only 20db of isolation you will have 15 watts coming
back while transmitting 1500. If you have 30 db you can see 1.5 watts with
1500 being transmitted. As you can see 1.5 watts is a lot of return power to
be dumped into most antenna ports or even protection devices. Most receiving
antenna transformers may not be capable of handling the return levels
greater than a few watts so you may have to reduce the transmit power to
keep the cores from saturating and use only the power necessary for a
measurement. Regards Lee K7tjr Oregon
|