Re: Walter's Telephones [Telecom]

[channel-6 LPTV as FM "radio" station]

47 CFR 73.653 (which is incorporated by reference into the LPTV rules in Part 74) provides:

The aural and visual transmitters may be operated independently of each other or, if operated simultaneously, may be used with different and unrelated program material.

So analog television licensees (at this point, only LPTVs) may broadcast video only, audio only, or both.

Combiners for broadcasting are generally built from a quadrature hybrid and a bunch of cavity filters. I have pictures of the combiner rooms at the Empire State Building and at the Hancock Tower in Chicago, but unfortunately I haven't published them yet. They look like rooms full of tanks, with lots of plumbing (rigid feedline) connecting them together. (Simple identification tip: Dielectric cavity filters are black rectangular prisms, whereas Shively filters are white or grey cylinders.)

Depends on the video system. System A (the old British 405-line system) and System E (the old French 819-line system) both chopped off the upper sideband. (System A originally used straight AM, before it was realized that VSB provided most of the benefits of AM while being more efficient in both power and spectrum utilization.)

It's the other way around: the video resolution is (well, was) determined by the bandwidth alloted for it.

-GAWollman

Reply to
Garrett Wollman
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No, Lisa, others have said that it cannot be used because it would cause interference to the *digital TV* station which is assigned that channel. This is not certain yet, and experiments are currently ongoing to determine the extent of and tolerance for such interference.

All existing NCE-FM stations give greater protection to the old channel 6 analog audio carrier than they do to FM broadcast stations assigned to comparable adjacent FM channels.

-GAWollman

Reply to
Garrett Wollman

=================================

Well, it's gone now, and it shall remain so for decades to come. Get used to it.

As at least two other posters (Garrett Wollman and me) have already explained to you, someone does indeed desire to use (and already is using) that particular frequency: namely, The Walt Disney Company, licensee of digital television station WPVI-DT.

I don't recall anybody saying that. It would not cause interference to other FM stations. However, it would certainly interfere with WPVI- DT's signal.

Neal McLain

Reply to
Neal McLain

I enjoyed reading Neal McLain's telling of his work with John Reiser. I think I first met John when we were both on a panel at the NAB (National Association of Broadcasters), probably one dealing with remote control of broadcast transmitters. At that time, the FCC required "fail-safe" control of the transmitter such that a failure in the circuit controlling the transmitter that prevented the operator from turning off the transmitter resulted in the transmitter going off. John expressed the FCC's flexibility in that rule by saying they didn't care how you turned off the transmitter. It would be OK to aim a cannon at the transmitter. I quoted him in a book I wrote for NAB on transmitter control and unattended transmitter operation. Since then, I often run in to John at NAB shows. I also get an occasional email from him, such as when he contributed the channel one article to my wiki.

He's a great guy!

Harold

***** Moderator's Note *****

Since many (most?) transmitters were controlled by voltages that were simplexed on the audio pair, I think the FCC's logic was that if the audio pair was cut or damaged, there'd be nothing to broadcast anyway.

Bill Horne

Reply to
harold

Not according to the newspaper. Apparently, surprisingly many people miss it and they're looking into bringing it back.

I don't understand. Several things suggest to me the digital and analog used _different_ frequences. (If in fact digital is using the same frequencies, yes, of course the issue of is moot.)

1) Before the digital switchover, TV stations were broadcasting in _both_ digital and analog. They would have tests pre-cutover where they'd tell viewers they were temporarily cutting off the analog signal. If the viewer could continue receiving, the viewer was set for digital, but if not, the viewer was not ready. 2) Further, I thought (as stated by others) that the digital signals were using different frequencies because the old analog ones were to be reassigned to other uses, such as public safety. But, Ch 6's old audio could not be reassigned because it was too close to other FM broadcast signals. 3) The newspaper article (admittedly not a technical document) suggested the problem was legal, not technical. Apparently dealing with royalty payments. They weren't issue when it was a 'quirk'.

When this was discussed in the other newsgroup, it seemed to me the only barrier was bureaucratic, not technical. There were long replies of various FCC rules; that if one took at their letter, either Ch 6 or consumer FM radio receiver manufacturers had been violating federal law for decades.

Frankly, I was troubled by the bureaucratic stance; I was hoping someone would take a consumer or public service stance. That is, instead of coming up with all sorts of _legal_ reasons why it couldn't be done, come up with a reason how it _could_ be done.

***** Moderator's Note *****

I'm not an expert on the subject: FWIW, here's my understanding.

  1. Some Analog stations were allowed to switch to Digital using the same range of frequencies (i.e., the same TV "Channel") that they previously used for Analog. Channel Six in NY was one of them. While the transition was in progress, I think those stations were _temporarily_ assigned UHF channels to use for Digital trasmission. It may be that Channel Six was allowed to skip the simulcast phase, i.e., it might have chosen to "flash cut" over to digital by disconnecting the Analog transmitter and hooking up the new DTV transmitter, both of which used the same TV Channel. I'll invite others to clarify this point.
  2. One of the stated aims of the DTV transition was to free up bandwidth in the lower frequency ranges formerly used by Analog broadcasts, so as to make those frequencies available for police, fire, homeland security, and other public safety uses. The unstated reason was that the federal government wanted to auction off the newly-available bands to commercial interests that would use them for the burgeoning portable device market, thus allowing more and faster services for users of Blackberry, Treo, and other portable devices. I'm not familiar enough with the differences between VHF and UHF TV bands to speculate on why the new services could not be assigned vacant UHF TV frequencies; again, I'll ask others to clarify this issue.

Some broadcasters, like Channel Six, got to keep their old assignments. I don't know if that was for technical reasons, such as the need to have a VHF assignment because of the peculiar terrain the station has to cover, or for other reasons. As I said above, I don't know if Channel Six used a temporary UHF assignment to simulcast its programs during the run-up to the transition, but whether they did or not is not germane to this discussion: the point is that the old Analog system is not compatible with the new Digital broadcasts, and a TV channel can be used for one or the other, but NOT both. Since Channel Six is now a DTV station, there is not, and cannot be, any FM audio carrier at 87.75 MHz for anyone to listen to.

  1. I don't know which newspaper article you're refering to, nor why royalty payments would apply. Please provide more background info.

Bill Horne

Reply to
hancock4

If that is the case the issue is moot since the frequency is in use.

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"One problem is that if 6ABC were to broadcast its content specifically for radio, the Philadelphia TV station would have to secure new intellectual-property rights. Under the pre-June 12 broadcast situation, people could hear the 6ABC shows basically by accident. So 6ABC did not have to acquire intellectual-property rights to be heard on radio."

Reply to
hancock4

None of the stations I worked with put their control on their program line. The program lines were generally driven with a WE 111C transformer to drop the 600 ohm source resistance (studio equipment) down to 150 ohms to drive the line. Another 111C converted it back to

600 ohms at the transmitter. There was then an equalizer (parallel resonant LC with a series pot) across the transmitter site transformer secondary. That then drove the transmitter site equipment (typically an audio limiter).

Control was generally on another pair (or two). The first system I worked with was a Gates RDC-10. It used different voltages and polarities on each wire of the pair to ground. One wire was held at a constant voltage by the RDC-10 "filament" switch. At the transmitter site, relays and steppers would interpret the control signal and send the metering sample back on a second telco pair. During my first FCC inspection, the inspector shorted out the control line and told me the transmitter was supposed to drop. I pointed out that the rule said "line faults causing loss of transmitter control" were required to shut the transmitter down. I then turned off the RDC-10 filament switch, and the transmitter went off. So, we still had transmitter control.

The next remote control I worked with was the Moseley WRC25, or something like that. It used vacuum tube circuitry to put dial pulses (tone pulses) and other control tones on a single pair to the transmitter site. There, the tones were detected, drove a stepper that sent DC sample voltages back on the same pair for indication on an analog meter at the studio.

Next came the Moseley PBR-15 and TRC-15, which continued to use tone for control, but also returned metering as another tone on the same telco pair. These could also be used on STL, FM, or AM subcarriers (for AM, it was in the 20Hz to 25Hz area).

Harold (author of the NAB Engineering Handbook chapter on transmission control systems)

***** Moderator's Note *****

Never let it be said that I can't take a hint.

Reply to
harold

Yes, before the transition, all stations were *temporarily* assigned additional channels to use for digital TV. Authority to operate on the "extra" channels expired on June 12, 2009. Every TV station had to choose whether to make the temporary digital channel permanent (an option not available to all stations), change their original channel to digital (an option not available to all stations), or choose yet another channel. The Digital TV Table of Allocations was set up to favor stations that made the first choice, but because some stations' temporary digital channel was assigned in spectrum that was scheduled to be removed from television service, not all stations had that option. (Some stations were particularly unlucky, with "double out of core" assignments, and they had to build a temporary digital transmitter on one channel, and then a completely new permanent digital transmitter on a different channel.)

The VHF-low band is useless to anyone other than broadcasters or hams, and the broadcasters aren't too keen on it either -- there's way too much interference, particularly on the lower channels. Remember the noise you would see on your television set if you ran your vacuum cleaner while watching channel 3? In digital TV, you don't get sparklies in your picture, you get no picture at all.

Public-safety services are getting part of the 700-MHz band, formerly channels 52-69.

You and I were obviously reading different posts.

[Now quoting our esteemed moderator:]

They were. Qualcomm MediaFLO, for example, has a nationwide license on the former channel 55, and was able to get its service to market before the transition by paying the occupants of that channel to shut down early. There are two reasons why no non-broadcast users have any interest in the VHF-low band:

1) The wavelength is far too long. Think about how big a ham antenna for the six-meter band is. Even a quarter-wave dipole is more than a meter long, which is far too large for any modern handheld device. 2) There is too much interference. You could build sufficient forward error correction (FEC) into the protocol to handle local, man-made interference, but Mother Nature gives us E- and F2-skip on that band, which makes it unsuitable for emergency services and other uses where the utmost reliability is required. In any case, while 700-MHz UHF does suffer from tropospheric ducting, there isn't nearly as much noise on these bands, so less bandwidth is required there to get the same amount of data through.

WPVI had a transitional digital assignment in part of the UHF band that had already been reassigned to non-broadcast service. For various reasons, there were no "core" UHF or VHF-high channels available in Philadelphia after the transition that they could have moved to.

They may soon be joined in the Roxborough tower farm by a station being moved in from Wyoming, which will operate on channel 3. The owners of the station found an obscure section of the Communications Act that allows this, and channel 3 is the only feasible channel currently available. (In this case, they don't care about over-the-air reception; the channel-3 license is only required in order to force their programming onto cable and satellite systems.)

-GAWollman -- Garrett A. Wollman | The real tragedy of human existence is not that we are snipped-for-privacy@csail.mit.edu| nasty by nature, but that a cruel structural asymmetry Opinions not those | grants to rare events of meanness such power to shape of MIT or CSAIL. | our history. - S.J. Gould, Ten Thousand Acts of Kindness

***** Moderator's Note *****

Given the likelyhood of interference due to the upcoming sunspot cycle maxima, I'd have thought broadcasters would be overjoyed to abandon VHF-Low assignments if favor of UHF. As you point out, the license is mostly an excuse to get on the cable or up to the Clarke Belt, but over-the-air viewers still count for Neilson ratings, so why would a station choose to keep a VHF-Low assignment if they had a choice? It meant converting to DTV twice instead of just once, so why not just convert to a UHF DTV channel, and stay there?

Reply to
Garrett Wollman

I've been Googling the DTV transition assignments, and came up with this document, entitled "DTV Tentative Channel Designations for the First and Second Rounds":

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.... which says that WPVI was assigned UHF channel 46 for DTV transmission. The document doesn't say what "first and second rounds" are (or were), but since others have said WPVI is using VHF Channel 6 for DTV, I assume they were the transitional phases of the DTV switch, during which WPVI simulcast it's programming to the DTV audience on channel 46.

This thread has gotten me curious: does anyone have the URL for the list of VHF channels that *were* retired/reassigned, and which ones are still available or in use for television? Does it vary by area, or is it the same throughout the U.S.?

I'd also like to have a list of stations which switched to UHF channels for their final DTV assignment, and which ones remained on VHF (or moved there after the changeover). Does anyone have a URL?

Bill Horne

Reply to
Bill Horne

Bill,

Try

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for a list of all DTV stations, their channel assignments and the cutover dates. It is organized by areas.

Eric T.

***** Moderator's Note *****

Thank you! That's perfect!

Some questions, after a quick look:

  1. Are the digital channel numbers the same as the old analog ones, i.e., does "Channel 12" occupy the same frequency range under the analog _and_ the digital assignments? I know that there are a lot of "Virtual" numbers that aren't actual frequency assignments, but the list shows some digital channels next to each other, such as channels 12 and 13 in Rhode Island, which used to be forbidden for analog stations.

  1. There are a lot more digital stations on VHF than I had expected, since I had been under the impression that (one of) the justifications for DTV was to "re-farm" allocations for new services and public safety. Was there ever a fixed range of frequencies that were to be reused for non-tv services, or are new services expected to be frequency-agile and able to slip into "white space" between the new DTV stations?

  2. If I wanted to help out all the little old ladies who still have rabit ears, could I rebroadcast the DTV stations onto analog channels? Are there still translators in existence that do that?

Bill Horne

Reply to
Eric Tappert

Twentyfive years ago, when I had a dozen+ LMC's for pipeline control; we were getting told by Ma that She would not give us an new inter-CO metallic circuits [i.e. DC connectivity], and the ones we had were subject to shutdown any time. Further, no guarantee as to how long intra-CO metallic ones would be available.

This was because inter-CO copper was being retired in favor of T Carrier. I'd assume N-Carrier [an analog mux scheme noted for causing global warming due to its array of vacuum tubes...] was also being scrapped but that's not germane here.

-- A host is a host from coast to snipped-for-privacy@nrk.com & no one will talk to a host that's close........[v].(301) 56-LINUX Unless the host (that isn't close).........................pob 1433 is busy, hung or dead....................................20915-1433

***** Moderator's Note *****

The push to install T-Carrier had an unintended consequence: many local municipalities were using "dry" pairs to interconnect parts of McCulloch-loop alarm systems, mostly used by burglar alarm systems, but sometimes even for fire alarms. The McCulloch Loops were set up like the original telegraph circuits, with negative voltage feeding one side of the loop, and positive feeding the other, so that if any part of the loop went open, the stations on either side of the break could still signal using ground return. Most municipal fire alarm systems that use Gamewell boxes still operate this way.

When told they would have to switch to tone or data-based alarms, the municipal managers screemed so loudly that Ma Bell bid a hasty retreat, and ordered D-4 boards which could repeat McCulloch Loop signalling. The towns and hamlets got to keep their investments in McCulloch Loop equipment going, and Ma Bell got to put the trunk pairs to better use.

That compromise would normally be called a "Win-Win" scenario, but T-Carriers turned out to be much less fault-tolerant than DC circuits on dry pairs, because, as I said, the McCulloch Loop devices could still signal with one side of the circuit open. With early T-Carrier spans suffering high failure rates, some mayors and city managers went to the PUC in their states and demanded that they be given access to dry pairs again. AFAIK, such requests were granted on an "As available" basis, but ONLY to government agencies, not to commercial BA providers such are Atlas, Wells Fargo, etc.

Reply to
David Lesher

In most cases the stations want to be identified by their old analog assignment and have chosen that for the PSIP channel identification. The RF frequencies are the same. Adjacent channels are allowed if about the same power level from the same retransmitting site ([just] like CATV).

The spectrum removed from TV service is UHF channels 52-69.

I suppose you could get a DTV converter and an RF modulator to do that job. The coupon DTV converters all have channel 3/4 modulators though.

David

Reply to
David

======================================================

Bill:

Assuming the FCC's chart is up-to-date, the digital channel numbers in use now (as in today) are (or should be) what the chart says they are. A chart showing the temporary assignments in use before the transition date is at

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As for your hypothetical "Channel 12", the digital may or may not occupy the same frequency range that Channel 12 analog occupied. Subject to some limitations, every (well, almost every) station could choose to remain in its temporary digital channel or return to its old analog channel. See Wollman's post of Jul 27, 12:25 am.

Indeed there are. Many (most?) stations have retained their old analog channel numbers for promotional reasons even if they're actually on a different channel. Case in point: Philadelphia's KYW-TV is now on Channel 26, but still calls itself CBS3.

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I'm not sure I trust that chart. I can believe that 12 and 13 could be adjacent in Providence, but I doubt that there are three digital stations all operating on Channel 7 in Rapid City.

Neal McLain

Reply to
Neal McLain

Depends on how you word the question.

DTV and NTSC frequencies are still in good old Megahertz. They get talked about as channels by by some engineering types and yes they are the same as always. I've seen various labels for those channels: "RF Channel" "raw channel" etc. See that FCC spreadsheet for their term.

The viewer-seen "Channel" is now just a marketing logo. It has zero correlation with the engineering one. In a FEW cases, they will be the same [see below]; but stopped clocks, etc.

As others said, stations had the choice of a 1) new temporary frequency or a 2) new permanent one [or 3), move twice]. There were tradeoffs either way. With 1), they'd be able to use their existing antenna and maybe transmitter final stages; with the new digital modulator. I don't know how most NTSC transmitters did modulation, but will guess it was NOT at the last stage. Correction welcome.

With 2) They could plow money into the digital transmitter and antenna as a permanent investment.

Some fudged; I know WETA [RF-26] got RF-27 for DTV; I suspect they retuned, not replaced, that antenna.

The economic analysis is actually a LOT more complex. In The Good Old Daze, everyone wanted Low VHF [2-6] for max range aka market size. Then color came along, and 2 etc had more issues with subcarrier phase shifts and such.

Now, Low VHF greater multipath vulnerability is a bigger issue than with NTSC.

But the BIG factor in the Musical Chairs game is: market areas have changed. There was a time when that flyover state Chan 2 had a 1500 ft tower to get way out to Hooterville and Bugtussle; now there's less audience for Chan 2's ads over there. And the local cable system in those burgs gives them NBC from a bird.

And for a REAL joker; some large % of TV station ad revenue dollars are from {remember them?} local car dealers. There are far fewer of those and less Detroit kickback money to pay for TV, etc...

I always figured the channel {interference} protection rules had to go back to Philo and DeForest; ISTM there were not just adjacent no-use areas, but also IF image ones, harmonics, images of harmonics, and you name it. One reason is obvious; think about the selectivity and image rejection of the circa 1930 tuners. I assume the FCC could/did use the DTV adventure to /dev/null many of those old rules.

There was no plan to reassign VHF TV space to others users, but a chuck of the UHF was peddled off at a very tidy sum. [THAT was the real instigator of the whole process; the Hill wanted to auction off spectrum space to cellco's to Make Money Fast...but they had to make the TV lobby happy too.]

A very good place to look for ALL kinds of data is the "AVS forum" site. They have some participants who know their stuph. One guy runs -- it's useful enough I bet even the FCC checks there.

Another note. Both the ABC & CBS outlets in DC, WJLA & WUSA, old 7 &

9, used the 1) plan above. When D-Day came, and they abandoned their temporary UHF slots; they were flooded with complaints by people who could no longer receive them, but had in NTSC. [As well as those who needed to rescan..] Even the WashPost Technology editor was a victim.

No one has yet to offer a lucid explanation as to why their DTV coverage was so much poorer than predicted. One or both got interim power increases [I am GLAD I was not working at the FCC Broadcast Bureau that week...] but have nearby co-channel neighbors as well. [Maybe Delaware in one case; I don't recall.] In any case, there are unhappy campers out there still.

One last thing to recall. The very last people to want more space, ergo more stations, to be available are those current license holders. The value of that piece of paper is inversely proportional to the number of competitors.

Reply to
David Lesher

PS to my previous post ...

I suppose three stations could share one DTV channel ... FOX on 7.1, ABC on 7.2, and NBC on 7.3 or something like that. Or, in view of the fact that there are two affiliates in the DMA for each network, maybe there's sufficient spacing to allow three Channel 7 transmitters to operate simultaneously without co-channel interference.

Neal McLain

Reply to
Neal McLain

Bill et al.

Answers in-line.

E. T.

Yes and yes. Same channel frequency assignments, just a shuffle of channels and a change of modulation... The virtual channels are just to keep the TV station identity the same. The old channel 10 may now be on a different frequency assignmentl, but your tuner can tune it by being told it is "10.1" even though it is somewhere in the UHF band. Also digital allows multiple subchannels. I get some channels with up to 5 different programs in the same frequency band as one "channel". Accordingly, you need 10.1, 10.2, 10.3, etc. to pick the right bitstream. It really is kind of neat. I used to get 12 channels over the air, now I get 31 (counting all the subchannels). Some old ones no longer come through, but there were some new ones...

Not knowing the inner thinking of the FCC, I can't answer this one... I suspect that the channels that are freed up are being used for other (non-TV) services that don't geographically extend beyond the old TV channel range.

My understanding is that all full power stations are now digital and the low power ones will have to convert in the next couple of years. The rabbit ears will work (with a converter box for an analog TV) for the VHF channels. There are "rabbit ear" type antennas for the UHF channels, so the little old ladies just need a converter box (which puts DTV channels on analog channel 3 or 4 on an RG-58 cable or an S video output for newer sets) and an indoor antenna that covers both the VHF (rabbit ears) and the UHF bands. Actually rebroadcasting over the air requires a license and there will be no more analog TV licenses in a couple of years.

Reply to
Eric Tappert

In point of fact, they were not given a choice about it. The DTV rules in effect on transition day required that stations use their old analog channel as their virtual channel. The FCC has shown some flexibility since then, mostly for stations that were "double out of core" before the transition.

-GAWollman

Reply to
Garrett Wollman

Actually, that's entirely possible, assuming they are all the same station, because the FCC now allows something called a "distributed transmission system": instead of using one big facility to serve their allocated coverage area, stations may elect to use multiple smaller transmitters, possibly with directional antennas, to serve their markets. A number of stations made the transition using DTS to reduce the cost, particularly in rural areas where an omnidirectional antenna would waste a lot of energy over sparsely-populated parts of the market.

-GAWollman -- Garrett A. Wollman | The real tragedy of human existence is not that we are snipped-for-privacy@csail.mit.edu| nasty by nature, but that a cruel structural asymmetry Opinions not those | grants to rare events of meanness such power to shape of MIT or CSAIL. | our history. - S.J. Gould, Ten Thousand Acts of Kindness

***** Moderator's Note *****

Please tell us about the various combinations of mode and signal available to digital stations. For example, if a station has two separate broadcasts going on, as does channel 7 in Boston, are they both being transmitted as part of the same digital stream, or are they only logically linked and transmitted on separate physical channels?

What about channel 44 in Boston? It has four separate subchannels: are they all just slots in one large bit stream coming out of WGBX's transmitter?

I ask because I regularly get dropouts and pixelation on 7-2 when 7-1 is coming in OK, and likewise have trouble with 44-3 or 44-4 when

44-1 is fine. If they're all part of the same bit stream, why does the problem affect only some of them and not all?
Reply to
Garrett Wollman

WETA uses a Dielectric TUP-O4-12-2 antenna, a high-gain broadband UHF panel antenna, which was installed a few years ago for the transitional DTV facilities of WJLA and WUSA, at a different site from the old channel 26 analog. So, no "retuning" required, or indeed possible. (The old tower, if I remember correctly, was in Virginia; the new tower is in far Northwest DC at the Maryland line.)

The rules have changed over time, and the FCC's approach to the rules has also changed. The FCC no longer models TV facilities using fuzzy photocopied charts derived from experiments done in the 1950s; now everything is done using the Longley-Rice propagation model. Furthermore, new TV allocations must follow a set of distance constraints in addition to the contour-overlap constraints, of which the most significant is the "donut hole" first-adjacent-channel taboo, which requires adjacent channels to be either very close or very far apart.

It seems widely agreed that the FCC's modeling did not accurately reflect real-world coverage of VHF DTV operations. (The fact that they assume everyone has an outdoor antenna ten meters off the ground doesn't help.) VHF-low band, in particular, had its initial maximum power rule very low, compared to VHF-high or UHF. There was also the issue that converter boxes were not required to include FM traps to be part of the coupon program, so people who bought them, live in markets with DTV on VHF-low, and live near an FM station lost big time.

It's the Media Bureau these days.

-GAWollman

Reply to
Garrett Wollman

,

====================================================

Garrett:

After further thought, I agree that it's entirely possible, particularly in a huge DMA like Rapid City. That DMA covers counties in four states, two of which are isolated islands inside other DMAs. Those isolated counties may be served by translators of Rapid City stations, or they may have separate stations.

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However, your statement "assuming they are all the same station" doesn't fit the situation I just described. The three Channel 7 stations in the Rapid City DMA 7 have separate call signs and they're affiliated with different networks. One of them (KSWY) is in Sheridan County, WY, one of those isolated counties (I should have recognized the Wyoming area code!).
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Neal McLain

Reply to
Neal McLain

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