Re: Hailing channel and intermodulation suppression

John Lloyd <lloyd@...>


Use a couple of good UHF bandpass cavities, at least 4" diameter in series with the UDR56K to the antenna. Tune them to the simplex frequency that you will be using. This will protect most problems for both your receive as well as transmit and others on the site.

John Lloyd, K7JL

Tom Hayward wrote:

Another thought... Maybe the power density is low enough that we won't
bother anyone with intermodulation interference. Would still need to
convince the site manager of this.


On Mon, Jun 24, 2013 at 9:24 AM, Tom Hayward <esarfl@...
<>> wrote:
> 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
>> 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

Join to automatically receive all group messages.