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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