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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

Tom Hayward <esarfl@...>
 

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.

Tom KD7LXL

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 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

John Lloyd <lloyd@...>
 

Tom,

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.

Tom KD7LXL

On Mon, Jun 24, 2013 at 9:24 AM, Tom Hayward <esarfl@...
<mailto:esarfl%40gmail.com>> wrote:
> On Sat, Jun 22, 2013 at 10:42 AM, siegfried jackstien
> <siegfried.jackstien@...
<mailto:siegfried.jackstien%40freenet.de>> 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