Re: Hailing channel and intermodulation suppression


Tom Hayward <esarfl@...>
 

On Sat, Jun 22, 2013 at 10:42 AM, siegfried jackstien
<siegfried.jackstien@...> wrote:

Repeater builders use a highpass lowpass combination (procom 70/6 or
similar) to transmit and receive on the same antenna ... now my rough guess
is that you could add such a filter to your antenna input and can transmit
on one frequency without desensing on the other frequency
Sorry for the delayed response. I was away from Internet all weekend.

The problem is not desense. The UDR56K is half-duplex so I don't need
to worry about desensing the receiver during transmit. And all the
other receivers on the site have bandpass filters so that is not an
issue. The problem I am trying to prevent is signals from nearby
transmitters mixing in the final amplifier of the UDR56K and causing
intermodulation interference. This is accomplished by using an
isolator/circulator to send any signal coming down the antenna into a
dummy load before it reaches the UDR's amplifier. Every
isolator/circulator I am familiar with has a very narrow bandwidth, so
by implementing this technique I would sacrifice the frequency agility
of the UDR56K, the integral feature of "A Hailing Channel for Packet
Radio".

Tom KD7LXL

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