WDCR-AM 1340

Dan.Strassberg dan.strassberg@att.net
Thu Aug 20 06:17:56 EDT 2009

Filters for diplexing of AMs present an analog design problem. I am
skeptical of any formula that specifies the minimum frequency spacing
directly in kHz, irrespective of the stations' dial positions. The
rule of thumb with which I am most familiar is that the frequency
difference should exceed 10% of the carrier frequency of the station
whose carrier frequency is higher. This rule is nowadays often
violated. Some of the most exotic arrangements are in Honolulu, where
triplexes are common and I'm pretty sure that there is at least one
quadriplex and there may be several. Thank goodness that there are
almost no (or maybe just no) directional AMs in Hawaii. The one on 870
(KAIM?) is no longer directional (I think it has also moved from 870),
but there may still be a directional AM elsewhere in Hawaii.

In any event, using the frequency difference as a percentage of the
higher carrier frequency, the two most closely spaced (in frequency)
diplexed AMs are in Santa Barbara on 1290 and 1340. 50 kHz is only
3.73% of 1340 kHz. I have no idea what the audio sounds like but I
suspect it's pretty muddy (no highs). Locally, WRCA and WKOX (just
barely) violate the 10% rule of thumb. 130 kHz is 9.77% of 1330. WBIX
used to diplex with WKOX during the daytime (1200-1060)/1200=11.67%. A
second closely spaced pair (signfiicant because they are relatively
high-powered stations sharing a complex DA) are 1370 and 1500 in San
Jose. These violate the 10% rule 130/1500=8.67%. The most closely
spaced diplex of two 50-kW AMs is probably 820 and 950 in Seattle

Long ago, 560 and 610 in SanFrancisco were diplexed 50/610=8.2%. 610
is still diplexed, but with a station on 1400 (no frequency-spacing
problems with that one!). And 610 is still ND-U, but in those old days
560 was also ND-U.

Note that not all cases of AMs sharing a site are diplexes. For
example, in Philadelphia, 860 and 950 share a four-tower site, but it
is not a diplex. 860 is a daytimer and 950 uses the site only at
night. In Syracuse NY, the owner of 1490 and 1540 was planning to have
both stations operate from the same site but use different towers. I
don't know, however, whether he ever moved 1540 to the 1490 site.
Sites that are shared but not diplexed present fewer filtering
problems than do true diplexes.

Dan Strassberg (dan.strassberg@att.net)
eFax 1-707-215-6367

----- Original Message ----- 
From: "Paul B. Walker, Jr." <walkerbroadcasting@gmail.com>
To: "Garrett Wollman" <wollman@bimajority.org>
Cc: "Dan.Strassberg" <dan.strassberg@att.net>; "bri"
Sent: Wednesday, August 19, 2009 11:50 PM
Subject: Re: WDCR-AM 1340

> Just because "West Lebanon"  doesn't exsist as an independent place
> to be
> served, doesn't mean someone can't try.
> Applications for new AM stations in "West Simsbury, CT" and "June
> Park, FL"
> come to mine.
> The later being nothing more then a mobile home park of a few
> hundred people
> in West Melbourne, FL (which IS a town!)
> 1490 WUVR is far enough away frequency wise where a diplex would
> work. The
> reccomended distance is usually at least 180Khz, but I've seen it as
> close
> as 80Khz in one case at the very upper right end of the dial in
> Orlando,
> Florida.. and it was a disaster.
> Comparing WUVR's coverage on 1490 with 640W, WDCR with 1KW would
> cover
> Hanover just fine by day, but it would be questionable at night,
> depending
> on a number of factors including incoming interference, efficeny of
> the new
> tower, etc
> Paul Walker
> www.onairdj.com
> On Wed, Aug 19, 2009 at 10:41 PM, Garrett Wollman
> <wollman@bimajority.org>wrote:
>> <<On Wed, 19 Aug 2009 22:27:27 -0400, "Dan.Strassberg" <
>> dan.strassberg@att.net> said:
>> > These days "wouldn't be any problem" usually turns out to be an
>> > overly
>> > optimistic assessment, even with little ND Class C AMs. They must
>> > now
>> > serve at least 80% of the CoL population at night, and with the
>> > high
>> > NIF's on graveyard channels, that often turns out to be either
>> > difficult or impossible to accomplish. For example, doing it from
>> > a
>> > cell tower that is not also used by another Class C AM licensed
>> > to the
>> > same community can be quite problematic in communities in which
>> > the
>> > population is not tightly concentrated in a small geographic
>> > area.
>> But if Vinikoor's 1490 can do it from a cell tower in Lebanon, then
>> a
>> 1340 could presumably work there too (assuming there are no issues
>> with adjacent channels).  (It turns out, by the way, that I was
>> wrong:
>> Lebanon is a city, so West Lebanon doesn't exist as an independent
>> place to be served.  The 1490 is licensed to Lebanon and was
>> granted
>> as a new station in 2004 from the last AM window in 2000.)
>> -GAWollman
> -- 
> Sincerely,
> Paul B. Walker, Jr.
> www.onairdj.com
> walkerbroadcasting@gmail.com

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