Michael,
You can't really "measure" the sensitivity of a repeater with an iso-tee
fitting, since there is nothing to compare it to as a reference. An
iso-tee is often used to assess receiver desense, but a better method
uses a test antenna. It is necessary to break into the feedline to
install an iso-tee, and that very act alters the configuration of the
system, which may invalidate the results. After all, as Kevin Custer
likes to point out, everyone else has to come in through the antenna, so
that's where the test signal should enter.
The method I use is simple and widely used. I have a magnetic-mount
whip that I can stick on the roof or the wall, on the outside of the
equipment shack. The whip is connected to the output of my service
monitor, which can generate a signal level as high as +30 dBm. I hook
up the SINAD leads to the speaker output of the repeater's receiver, and
I disable the transmitter so it won't repeat. I generate a signal on
the receive frequency, and set the level for 12 dB SINAD. I then enable
the transmitter, and observe the SINAD meter for movement. A good
repeater will not budge the needle, indicating zero desense. A poor
repeater will have more than 1 dB of desense. As you might imagine,
very few 2m repeaters make the grade with only a four-cavity duplexer.
More often than not, the owners of such repeaters are unaware of this
performance impairment!
73, Eric Lemmon WB6FLY
Michael Singewald N1PLH wrote:
>
> A while back, the conversation was about bench sensitivity versus
> real world sensitivity. I would like to test the sensitivity of our
> repeater rx while hooked up to the duplexer, feedline and antenna.
>
> I think I need some kind of T connector to put between the duplexer
> and receiver. I don't think it would be a standard T, so my question
> is what exactly do I need?
>
> Thanks
>
>
> Yahoo! Groups Links
>
>
>
>
Yahoo! Groups Links
<*> To visit your group on the web, go to:
http://groups.yahoo.com/group/Repeater-Builder/
<*> To unsubscribe from this group, send an email to:
[EMAIL PROTECTED]
<*> Your use of Yahoo! Groups is subject to:
http://docs.yahoo.com/info/terms/
