Try putting a one inch dia, single turn loop on the end of a coax
feed line to a receiver. Use it to sniff around inside the box to find the RF.
73 de KN6TD
(s) Derek
At 11:42 AM 8/31/2008 -0400, you wrote:
I've tried everything, it seems, and I still have desense!!
Even when I connect only the repeater (Yaesu Musen FTR-1510) and a
controller (needed to make the repeater transmit) and put a dummy
load on the TX out, I get desense.
Following up on Eric's suggestion about holes leaking RF, I sealed
the edges and holes in the TX and RX units inside the repeater, and
I built a shield to enclose the back side of the TX connector that
is on the back side of the repeater. That might have reduced the
desense a little bit, but not much.
I even ran the TX feedline to an outside wire-mesh chair in an
effort to reduce any possible radiation getting from the dummy load
to the receiver. There was still the same desense.
The desense is at least 10 dB.
It appears to me that the desense has to be occurring inside the
repeater cabinet, but for the life of me I can't see how this can
be. Everything seems to be well shielded.
So, I'd very much like to hear your theories and suggestions. Is
there some way to find the source of the desense radiation? Is there
some way that unshielded control lines, audio lines, and power lines
can carry RF to the receiver?
I have looked at the output of the repeater TX with a spectrum
analyzer [tnx Tom N4ZPT] and it is clean.
While I don't think the following is significant, for completeness I
note that the repeater RX and TX both appear to be several kilohertz
low in frequency. However, I do not have a frequency counter, and I
am only checking the frequencies by the use of an HT and mobile,
both modern transceivers by Yaesu.
Your thoughts, suggestions, and sympathy will be appreciated.
John
AF4PD
