Theory Discussion: Circular Polarization Vs. Vertical Polarization

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Paul678
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Re: Theory Discussion: Circular Polarization Vs. Vertical Polarization

Post by Paul678 » Wed Nov 09, 2016 9:53 am

w9wi wrote:[img]http://www.w9wi.com/images/KRRN.jpg

Legal reasons. See the image. (assuming it works :) if not, try http://www.w9wi.com/images/KRRN.jpg )

We're looking at KRRN, 92.7MHz in Las Vegas. Legally, KRRN is NOT a Las Vegas station -- it's authorized to serve Moapa Valley, Nevada.

KRRN cannot locate its transmitter any closer to Las Vegas than it has. The lime green circle on the map is the interfering radius of the KRRN transmitter -- the area in which its signal is strong enough to interfere with stations KOMP (92.3MHz) and KYMT. (93.1MHz) The red circle is the area in which KOMP and KYMT are protected from interference. Note that the circles touch but don't overlap. Note the location of Las Vegas on the map -- at the outer edge of the area reached by the KRRN main transmitter. Note that there isn't much population within the green circle, except in the southwestern corner.

The irregular blue area is the area served by KRRN's booster. Note that this encompasses nearly all of the city of Las Vegas -- and not much else. Note mountains northeast of Las Vegas: the signal from the main KRRN transmitter is probably considerably weaker in the city than the green circle suggests. (if it wasn't, the booster would interfere with the main)



My point is.. most of the area covered by the booster is populated. Most of the area covered by the main transmitter isn't. The main transmitter must be located where it is because of FCC regulations. (I'm sure KRRN would rather its transmitter be located on the same mountain as KOMP and KYMT, but the regulations say otherwise) A booster won't be licensed unless it has a main transmitter to boost. (I'm sure KRRN would rather not bother building & operating the main transmitter, but they can't legally operate the booster if they don't)

So the main transmitter exists solely to justify the booster, and will be operated as cheaply as possible. The booster exists to reach Las Vegas, and it's worth investing in a circularly-polarized plant.
That's crazy! If I understand you correctly, the booster could be made into the main transmitter, and the listeners wouldn't notice
the difference!

But even as-is, doesn't the booster itself have an interfering radius that is within the red circle, the area protecting KOMP and KYMT? Or is the booster's interfering radius much smaller, and will not penetrate Las Vegas, and can legally be ignored?

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Deep Thought
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Re: Theory Discussion: Circular Polarization Vs. Vertical Polarization

Post by Deep Thought » Wed Nov 09, 2016 11:36 am

Paul678 wrote:But even as-is, doesn't the booster itself have an interfering radius that is within the red circle, the area protecting KOMP and KYMT? Or is the booster's interfering radius much smaller, and will not penetrate Las Vegas, and can legally be ignored?
Boosters are licensed under Part 74 in the same rule section as translators, and can be ordered off the air should they cause "actual interference" just as translators can. The primary limiting factors for booster operation are the 60 dBu of the booster must be wholly within the 60 dBu of the primary, and it cannot exceed 20% of the ERP of the primary station's ERP (adjusted for primary station antenna height if necessary).
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Re: Theory Discussion: Circular Polarization Vs. Vertical Polarization

Post by w9wi » Wed Nov 09, 2016 12:39 pm

Paul678 wrote: That's crazy! If I understand you correctly, the booster could be made into the main transmitter, and the listeners wouldn't notice
the difference!
True: they could shut down the main transmitter & operate only the booster and nearly all the audience wouldn't notice the difference. It would however be contrary to the rules.
But even as-is, doesn't the booster itself have an interfering radius that is within the red circle, the area protecting KOMP and KYMT? Or is the booster's interfering radius much smaller, and will not penetrate Las Vegas, and can legally be ignored?
Deep has the answer to this part. As a practical matter, note that the booster is located outside the populated area of Las Vegas which makes actual interference less likely. That, and modern radios are far more selective than they were in 1964 when the framework of the current rules was established. But if anyone complains of interference, the booster must be shut down until (and unless) the interference is resolved.
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Re: Theory Discussion: Circular Polarization Vs. Vertical Polarization

Post by Paul678 » Wed Nov 09, 2016 1:36 pm

w9wi wrote:
Paul678 wrote: That's crazy! If I understand you correctly, the booster could be made into the main transmitter, and the listeners wouldn't notice
the difference!
True: they could shut down the main transmitter & operate only the booster and nearly all the audience wouldn't notice the difference. It would however be contrary to the rules.
But even as-is, doesn't the booster itself have an interfering radius that is within the red circle, the area protecting KOMP and KYMT? Or is the booster's interfering radius much smaller, and will not penetrate Las Vegas, and can legally be ignored?
Deep has the answer to this part. As a practical matter, note that the booster is located outside the populated area of Las Vegas which makes actual interference less likely. That, and modern radios are far more selective than they were in 1964 when the framework of the current rules was established. But if anyone complains of interference, the booster must be shut down until (and unless) the interference is resolved.
But aren't these archaic rules a bit silly, if the booster can supply nearly all the required signal?

Can't they re-write the rules for modern, high-Q filters with better out-of-band rejection?

And even if the booster is less than 20% of the ERP of the main transmitter, there will still technically be an interference radius around it.

Seems to me the only benefit of this situation is that if the booster is shut down for interference, you'd still have a signal (albeit weaker) on the air from the main, so maybe that's the justification.

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Re: Theory Discussion: Circular Polarization Vs. Vertical Polarization

Post by w9wi » Wed Nov 09, 2016 9:35 pm

Paul678 wrote: But aren't these archaic rules a bit silly, if the booster can supply nearly all the required signal?

Can't they re-write the rules for modern, high-Q filters with better out-of-band rejection?

And even if the booster is less than 20% of the ERP of the main transmitter, there will still technically be an interference radius around it.

Seems to me the only benefit of this situation is that if the booster is shut down for interference, you'd still have a signal (albeit weaker) on the air from the main, so maybe that's the justification.
Absolutely, there is still an interference radius. Most of it will fall in a place where there are no people - I suppose they're hoping the rest, nobody will notice. I note the booster has been licensed since 2008 so apparently they have chosen well:)

The justification is that, from a legal standpoint, the community served by KRRN is NOT Las Vegas. It's Moapa Valley. The FCC is charged with providing a "fair distribution" of service. Authorizing another signal to Las Vegas (which already has fifteen FM stations) is a far lower priority than providing a service to Moapa Valley. (which only has two, counting KRRN)

I suppose they could rewrite the rules to acknowledge the more-selective receivers. Canada has -- allowing same-site frequency separation of only 600KHz, vs. 800KHz required in the U.S.. I'm hearing Mexico has just reduced the required separation to 400KHz. If it were to be done in the U.S. I suppose KRRN might be one of a very small number of stations which might be able to take advantage. (it won't be done here, nobody is asking for it and I suspect existing broadcasters would fight a proposal) Since there *is* another station (KJUL 104.7MHz) authorized to serve Moapa Valley, KRRN could move to Las Vegas without leaving Moapa Valley without local service.

Such a change would have little or no impact on places like, say, Chicago, where all the 400KHz splits are occupied by suburban stations. You can't move the suburban station into the city because it would cost the suburb its only service -- and go counter to "fair distribution".
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Re: Theory Discussion: Circular Polarization Vs. Vertical Polarization

Post by Deep Thought » Thu Nov 10, 2016 12:32 am

Paul678 wrote:But aren't these archaic rules a bit silly, if the booster can supply nearly all the required signal?

Can't they re-write the rules for modern, high-Q filters with better out-of-band rejection?

And even if the booster is less than 20% of the ERP of the main transmitter, there will still technically be an interference radius around it.

Seems to me the only benefit of this situation is that if the booster is shut down for interference, you'd still have a signal (albeit weaker) on the air from the main, so maybe that's the justification.
"archaic"
"silly"

On what basis do you make these statements?

Do you know the history behind these rules? Are you prepared to replace >300 million receivers in order to assure proper operation? What would you do if I moved a booster to within a few miles of your station on an IF-related channel and wiped out most of your coverage within 5-10 miles of my booster? Would you think that was silly?
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Dale H. Cook
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Re: Theory Discussion: Circular Polarization Vs. Vertical Polarization

Post by Dale H. Cook » Thu Nov 10, 2016 8:08 am

Paul678 wrote:... I've never personally owned an FM modulation monitor. Can you recommend a reasonably priced one, with good features?
My personal favorite for an analog-only monitor is the QEI 691. Although they are out of production QEI still supports them. Because they were expensive not a ton of them were sold, and they seldom come up for sale. When they do appear it is not unusual to see an asking price of $700-800, sometimes more. They can be beasts to repair, especially for someone whose has never worked on one (I have almost 30 years of experience with the 691). My 691 is one that I used to use when I worked full time for the previous owner of a station. The current owner replaced it when he installed HD.

If the 691 is going to be transported Mark Persons has some good modifications:

http://mwpersons.com/tech-tips/FM/QEI-691-mod-mon.htm

I don't have any current FM clients, but do get occasional calls from former FM clients when their young engineers get up a creek with a major problem. I like to have my own 691 for some problems.

A good lower-end analog monitor is the Inovonics 530. It does not do AM, which is unfortunate as I work in mountainous territory where synchronous AM minimization can be a vital adjustment. There are other ways to accomplish that, though.
Paul678 wrote:What do you think about this page:

http://www.thebdr.net/articles/rf/ctl/W ... onitor.pdf
As Jim points out, a station without a mod monitor is like a car without a speedometer, which is why I own frequency agile AM and FM analog monitors (none of my clients, which are all small stations, do digital).
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Re: Theory Discussion: Circular Polarization Vs. Vertical Polarization

Post by BroadcastDoc » Thu Nov 10, 2016 9:30 am

Ah, yes. I have a 691 myself. Sorta works. ;-)
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Re: Theory Discussion: Circular Polarization Vs. Vertical Polarization

Post by W2XJ » Thu Nov 10, 2016 2:49 pm

Interesting drift of topics.

Regarding polarization: Vertical polarization is more rapidly attenuated as it leaves the transmitter and is more readily reflected so causes more multipath. Another point is that due to reflections, the polarity of FM signals is random in the field. Based on real world measurements, the CBC and most European broadcasters have determined HP is the better alternative. Some US stations have opted for elliptical polarization where the vertical component is a fraction of horizontal due to multipath issues.

Regarding stereo vs mono: This is simple math. Modulation index determines signal to noise. With stereo the index is 1.5 for a case where the transmitter is modulated single channel at 100% modulation. For mono the modulation index is 5. I have put on stations where we limited the audio bandwidth to 8 KHz for an index of almost 10. The higher the index, the greater the signal to noise and the more positive the effect on capture ratio. Many public radio stations are mono to improve coverage and mitigate multipath.

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Re: Theory Discussion: Circular Polarization Vs. Vertical Polarization

Post by Dale H. Cook » Thu Nov 10, 2016 4:12 pm

W2XJ wrote:Many public radio stations are mono to improve coverage and mitigate multipath.
I was CE for more than a decade at an FM News/Talk that was mono for the same reason.
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Re: Theory Discussion: Circular Polarization Vs. Vertical Polarization

Post by ChuckG » Thu Nov 10, 2016 6:46 pm

BroadcastDoc wrote:Ah, yes. I have a 691 myself. Sorta works. ;-)

Mine is the same. Kinda like a speedometer, sure. But one you can't trust.
<><><><><><><><><>
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Re: Theory Discussion: Circular Polarization Vs. Vertical Polarization

Post by Paul678 » Fri Nov 11, 2016 12:29 am

W2XJ wrote:Interesting drift of topics.

Regarding stereo vs mono: This is simple math. Modulation index determines signal to noise. With stereo the index is 1.5 for a case where the transmitter is modulated single channel at 100% modulation. For mono the modulation index is 5. I have put on stations where we limited the audio bandwidth to 8 KHz for an index of almost 10. The higher the index, the greater the signal to noise and the more positive the effect on capture ratio. Many public radio stations are mono to improve coverage and mitigate multipath.
There you go...you explained it better than me!

Thanks everyone, for the input....Circular polarization it is....if you can afford it!

:lol:

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Re: Theory Discussion: Circular Polarization Vs. Vertical Polarization

Post by Deep Thought » Fri Nov 11, 2016 10:13 am

Paul678 wrote:Circular polarization it is....if you can afford it!
If you can't afford it, you should reconsider your business plan. The antenna is one place skimping will universally come back to bite you in the ass.
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Re: Theory Discussion: Circular Polarization Vs. Vertical Polarization

Post by Paul678 » Fri Nov 11, 2016 1:06 pm

Deep Thought wrote:
Paul678 wrote:But aren't these archaic rules a bit silly, if the booster can supply nearly all the required signal?

Can't they re-write the rules for modern, high-Q filters with better out-of-band rejection?

And even if the booster is less than 20% of the ERP of the main transmitter, there will still technically be an interference radius around it.

Seems to me the only benefit of this situation is that if the booster is shut down for interference, you'd still have a signal (albeit weaker) on the air from the main, so maybe that's the justification.
"archaic"
"silly"

On what basis do you make these statements?

Do you know the history behind these rules? Are you prepared to replace >300 million receivers in order to assure proper operation? What would you do if I moved a booster to within a few miles of your station on an IF-related channel and wiped out most of your coverage within 5-10 miles of my booster? Would you think that was silly?
Are you implying the FCC has never changed any of its rules in its entire history? I highly doubt that!

It would be foolish to write their rules in stone, never to adapt them to new standards and new innovations in the RF world.

And it's completely silly and ridiculous that the main transmitter in this case does not significantly add to the signal given
off by the booster, and only exists for legal reasons.

Why not take the rules that allow the booster's interference radius to be within the red circle, and apply those rules to the main
transmitter, so that the booster itself can become the main?

That would be far more efficient and less wasteful.

But if you are obsessed with the rules as they are, then reason is hard to come by....

:wink:

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Re: Theory Discussion: Circular Polarization Vs. Vertical Polarization

Post by Deep Thought » Fri Nov 11, 2016 3:04 pm

Since all it seems you want to do is argue I'm done here. Enjoy your failed station.
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