[RTTY] Radio interference problem

[Roy Morgan]

At 09:45 PM 12/27/2005, K8JWT wrote:
>Sorry for adressing multiple reflectors but this problem is killing my 
>capabilities to operate.
>Any suggestions would be very helpful. . .


(This to only RTTY at contesting.com and K8JWT)


1) confirm that the source of the QRM is the monitor by unplugging it. (not 
just turning it off..the darned things have active circuits even though 
they appear to be off.)

2) Establish the route the QRM is getting into your receiver: Unplug the 
antenna input and put on a dummy load or a short at the antenna jack *on 
the back of the receiver*, not at the end of some coax.  A direct-short or 
50-ohm PL-259 is a *very* useful test item.

3)  A) If any of the QRM remains, continue to unplug wires to the radio 
until you know how the noise is getting in. Power cord last. Try battery 
power if your receiver will run on it.

B) If the noise is getting in via the antenna jack/front-end then 
investigate your antenna setup:  Coax connectors (PL-259's are not as good 
as BNC), The coax itself (if aluminum foil reduces the noise you can 
suspect incomplete shielding in the coax) or noise travelling along the 
outside of the coax (Ferrite beads/clamps, or coiling the coax will help 
confirm this), any coax antenna relays can leak a lot unless they are very 
high quality.  Put a short circuit or 50 ohm load AT the antenna to see if 
the noise is travelling from the monitor to the antenna and then back to 
the receiver.  This is a very revealing test to see just how "shielded" 
your coax system is. You may be surprised at how many stations you can hear.

C) If the noise is getting in via the power cord, make a two pronged 
attack: at the source and at the receiver: Ferrite clamp-ons, bypass caps, 
RF line filters, and the like.

4) If all else fails, get a copy of the ARRL book on interference and start 
at Page 1.

5) IF that fails, get rid of the monitor and get one that's quiet.

Roy


- Roy Morgan, K1LKY since 1959 - Keep 'em Glowing!
7130 Panorama Drive, Derwood MD 20855
Home: 301-330-8828 Cell 301-928-7794
Work: Voice: 301-975-3254,  Fax: 301-948-6213
roy.morgan at nist.gov --