Eric:
Were you able to determine if the 160M / BC interference from the stations
was fundamental overload or IM?
I've found both to exists however, many times the source is external to the
radio and thus is IM as a result of non-linear devices in the field of RF
from multiple sources.
In one case I solved, the interference was the result of transmitter IM
being from 5 different sources mixing in the PA of a VHF paging TX. Took
some good software to find this one and lots of listening to figure which 5
TX's was on the air when it happened. They were communications sources
which were of dispatch nature and thus only transmitting briefly. A
circulator was placed in the output of the offending TX and the problem was
solved.
These guys complain about BCI and IM. To that I say HA! My ORION is at a
5KW AM TX site. The 75M center fed antenna is tied to one end of the AM
radiator with the end insulator about 45 feet from the tower. To add insult
to injury, there is a 50KW SW AM station is about 2 miles away. It
operates mostly near the 40M band. Needless to say, there's a good bit of
RF around the ORION which is located about 30 feet on the desk from the BC
TX. NO BCI exists, no external filters required.
From my perspective, most hams don't have a clue as to what a "clean site"
actually is and most are very poor RF technicians with even a poorer
understanding of good engineering practice.
73
Bob, K4TAX
----- Original Message -----
From: "Eric Rosenberg" <wd3q@starpower.net>
To: <tentec@contesting.com>
Sent: Saturday, May 28, 2005 8:21 PM
Subject: Re: [TenTec] ORION BCI
I've been following the thread on BCI to the Orion with both interest
and amusement.
I live in Washington, DC proper, 5.5 miles from a 50kw AM station
operating at 1500 kHz (signal measured a -10 dBm with a lab-grade
spectrum analyzer on my inverted-L), and another relatively high power
AMer at 1260 kHz.
From my roof I can see (and have photos of) all of Washington's TV
(NTSC and HD) and FM broadcast towers, not to mention the plethora of
US and foreign government, commercial and other point-to-point
transmitters and repeaters that operate into the microwave bands and
seemingly beyond.
Regardless of the number and size of cavity filters, weak signal and
amateur satellite operations are difficult (I used to operate on AO-13
and to a lesser degree the pacsats) or impossible.
And the intermod/overload on 160 is pretty amazing, regardless of the
radio I've used... be it Kenwood, Icom, Yaesu or Ten Tec.
For the past 5 years, I had an Omni-6+. For the past year, an Orion.
The solution? Well designed and built BCI filters. I spent as lot of
time researching what was available in the amateur radio
world. Neither the ICE filter (402X), W3NQN, Top 10 Devices or anyone
else's worked for me. In the end, I did find one, not (yet)
commercially available filter that worked so well for me that I had my
best score ever in the CQ 160 contest! If and when it becomes
available, I'll post information here on the reflector.
A great resource for locating the broadcast (AM, FM and TV) stations in
your neighborhood is AMSTNS and TVFMSTNS by Bob Carpenter,
W3OTC. Bob's software was invaluable to me in identifying the local
broadcasters to better understand who and where and to what degree the
offending stations might be. An overview of the software is available
at http://users.erols.com/rcarpen/INFO0227.html while the latest
versions of the software are available at
http://home.earthlink.net/~lvehorn/ For best results follow the
various links!
The bottom lines is that if you're close to a broadcaster and suffer
from intermod and overload problems, don't blame it on the
radio! External filters are the only solution.
GL!
Eric W3DQ
Washington, DC
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