Half Wave, 5/8'S WAVE VERTICAL ANTENNA HELP!

[greg.hahn]

It all comes down to cost. Spend enough money and you can obtain good gain, cancel downward radiation and expand bandwidth with CP.

Translation: Vertical antennas are cheaper. True.

And DBX 166s are cheaper than Optimods.

Bottom line is you can buy more coverage area at a fraction of the cost using VP.

Not true. The true bottom line is that you can get on the air for less with a VP. You don't get the superior coverage you are suggesting. If you did, we'd all switch to it and be done.

 

[Shockwave]

It all comes down to cost. Spend enough money and you can obtain good gain, cancel downward radiation and expand bandwidth with CP.

Translation: Vertical antennas are cheaper. True.

And DBX 166s are cheaper than Optimods.

Bottom line is you can buy more coverage area at a fraction of the cost using VP.

Not true. The true bottom line is that you can get on the air for less with a VP. You don't get the superior coverage you are suggesting. If you did, we'd all switch to it and be done.

If you are able to compare a single CP bay against a single VP without changing any other variables, it will become clear to you also that VP provides the largest coverage area. I'm talking about simple RF engineering here not FCC regulations that benefit CP by authorizing the same ERP in both planes. VP is twice as efficient per bay, per watt. The main reason it hasn't taken off in the USA is the FCC.

 

[greg.hahn]

If you are able to compare a single CP bay against a single VP without changing any other variables, it will become clear to you also that VP provides the largest coverage area. I'm talking about simple RF engineering here not FCC regulations that benefit CP by authorizing the same ERP in both planes. VP is twice as efficient per bay, per watt. The main reason it hasn't taken off in the USA is the FCC.

Big deal.

Let's assume that it is true that a vertical is twice as efficient as a circular. The FCC would then only license you for half the power with the vertical that you would get on the CP. It comes back to the adage, "there is no such thing as a free lunch."

 

[rfry]

Richard did teach me something with the canceling of downward radiation in CP. Thank you!

You're welcome, and thanks for saying so.

I still suspect it's lower in VP without the need to cancel.

Suspicions and intuition are useful, to a certain point. An accurate mathematical evaluation supported with unbiased field experience and measurements are even better.

Analysis using Numerical Electromagnetics Code (NEC) shows that the c-pol elements I referred to have the same free-space elevation patterns as a vertical, center-fed, 1/2-wave dipole. All of these configurations show zero elevation pattern field at +/-90 degrees. But due to re-radiation from the supporting tower and its contents -- none of these radiator designs achieves this in practice.

Anyone wishing to investigate this might want to download one of the NEC programs available, construct and analyze the radiation performance of suitable models, and determine this for themselves.

Otherwise the antenna engineering textbooks of Kraus, Balanis, and Johnson/Jasik will lead to the same conclusion.

Also please note that US FM and TV stations are not permitted to use only vertical polarization without prior authorization from the FCC.

If you are able to compare a single CP bay against a single VP without changing any other variables, it will become clear to you also that VP provides the largest coverage area.

Your quote above is from a later post of yours, but you should have qualified it to apply to receiver systems responding only to v-pol transmissions. Not all FM receiver systems do so.

This is a moot point in any case, because the FCC licenses analog FM/TV broadcast stations for a given ERP per polarization, whether that is comprised of the H & V components of a c-pol system, or is linearly-polarized H or V.

So such a v-pol (only) transmit antenna has no greater coverage area to a receive system responding only to v-pol transmissions than if it was c-pol, other things equal.

//

 

[Shockwave]

If you are able to compare a single CP bay against a single VP without changing any other variables, it will become clear to you also that VP provides the largest coverage area. I'm talking about simple RF engineering here not FCC regulations that benefit CP by authorizing the same ERP in both planes. VP is twice as efficient per bay, per watt. The main reason it hasn't taken off in the USA is the FCC.

Big deal.

Let's assume that it is true that a vertical is twice as efficient as a circular. The FCC would then only license you for half the power with the vertical that you would get on the CP. It comes back to the adage, "there is no such thing as a free lunch."

Now we agree Greg. Remove the FCC from the equation and look at antenna performance only. No omni directional CP antenna does better then –3 dbd. Some verticals such as the Dominator are around +3dbd. That’s four times the efficiency of CP.

Remember, not everyone here is governed by the closed minded self-serving FCC. Shouldn’t the rules be designed to coincide with the use of the most efficient antennas rather then compromising the antenna to make the most efficient use of the rules?

I hate to think Israel, the UK, and the Netherlands are more advanced in this area then the USA. However, they were able to conduct in depth, in field studies on FM polarization over two decades ago. The conclusion after testing is that all three countries went with vertical polarization.

 

[greg.hahn]

Now we agree Greg. Remove the FCC from the equation and look at antenna performance only.

You can't just adjust the playing field to fit your argument. This is the "Engineering" forum on "Radio-Info.com. This forum describes itself as:

“Radio’s Online Community.” It’s built on the popular message-board framework Doug created and today provides both radio professionals and fans a valued source for news, expert commentary and the lively industry gossip that radio thrives on.


This particular forum is:

Engineering
Issues pertaining to broadcast Engineering


You can't just "remove the FCC from the equation" as much as your antenna company might like to.

 

[rrsounds]

If you are able to compare a single CP bay against a single VP without changing any other variables, it will become clear to you also that VP provides the largest coverage area. I'm talking about simple RF engineering here not FCC regulations that benefit CP by authorizing the same ERP in both planes. VP is twice as efficient per bay, per watt. The main reason it hasn't taken off in the USA is the FCC.

Big deal.
Let's assume that it is true that a vertical is twice as efficient as a circular. The FCC would then only license you for half the power with the vertical that you would get on the CP. It comes back to the adage, "there is no such thing as a free lunch."

Now we agree Greg. Remove the FCC from the equation and look at antenna performance only. No omni directional CP antenna does better then –3 dbd. Some verticals such as the Dominator are around +3dbd. That’s four times the efficiency of CP.
Remember, not everyone here is governed by the closed minded self-serving FCC. Shouldn’t the rules be designed to coincide with the use of the most efficient antennas rather then compromising the antenna to make the most efficient use of the rules?
I hate to think Israel, the UK, and the Netherlands are more advanced in this area then the USA. However, they were able to conduct in depth, in field studies on FM polarization over two decades ago. The conclusion after testing is that all three countries went with vertical polarization.

The reason the CP antenna seems 'less efficient' than the vertical-only, is the CP is distributing its signal into transmission in all polarities. This is not a bad thing!

When it comes to reception quality (and that IS what we're after, isn't it?!!) there are HUGE quality advantages to using CP, especially in difficult terrain, where reflections can cause radical distortions in a single-polarity signal.

Really, 3 dB, while noticeable, would not be a 'deal-breaker' in the first place. Moving/rotating an FM receiving antenna randomly in 3D space (automobile listening, anyone?) generally provides variations of a vastly greater degree (including complete nulls), and since practice proves these variations are somewhat overcome by CP transmission, by I'd say CP has it all over V-only, 'efficiency disadvantage' or not!

If the 3dB 'penalty' of CP's transmission to your vertical-only receive antenna bothers you, just get a CP receive antenna, and recover all that 'wasted' signal. ;-)

The FCC's engineering judgment concerning CP is one rare place where most of us agree they did the right thing.

Kind Regards,
David

 

[rfry]

If the 3dB 'penalty' of CP's transmission to your vertical-only receive antenna bothers you,...

Note that there is no 3 dB penalty in the radiated power of FCC licensed FM/TV stations using a c-pol transmit antenna.

It radiates just as much v-pol as a v-pol only antenna, because the input power to the c-pol antenna is set to the value needed to do so.

//

 

[greg.hahn]

If the 3dB 'penalty' of CP's transmission to your vertical-only receive antenna bothers you,...

Note that there is no 3 dB penalty in the radiated power of FCC licensed FM/TV stations using a c-pol transmit antenna.

It radiates just as much v-pol as a v-pol only antenna, because the input power to the c-pol antenna is set to the value needed to do so.

//

Hey, no fair! Now you're bringing that pesky FCC back into the equation.

 

[rrsounds]

If the 3dB 'penalty' of CP's transmission to your vertical-only receive antenna bothers you,...

Note that there is no 3 dB penalty in the radiated power of FCC licensed FM/TV stations using a c-pol transmit antenna.

It radiates just as much v-pol as a v-pol only antenna, because the input power to the c-pol antenna is set to the value needed to do so.

//

Exactly, Mr. Fry. Which is why I put the word penalty in quotes.

Kind regards,
David

 

[RadeoEngineer]

You know, there are quite a few truly brilliant RF engineers floating around out there (I'm not one myself) but if there was a better way to cover than C-Pol I would think this would have been big news a long time ago. I can see V-Pol for low power stations on a budget, but every facility I worked on in my 35 years was C-Pol, from the deep south to the west coast.

 

[Play Freebird]

I suppose the question that needs to be discussed is: Why doesn't the FCC allow full-service commercial FM stations the option to operate vertical only?

Horizontal linear polarization is legal, so why not vertical linear? The old "It shall be standard to employ horizontal polarization" rule was written in the 1940's, long before FM made its way into cars, and it needs to be reconsidered.

As I mentioned earlier in this thread, if money isn't a concern, I do understand the advantages of CP over linear polarization. However, some smaller stations on tight budgets could economize on power consumption if the horizontal component were eliminated and this would have little perceptible impact on signal coverage in many cases.

Of course translators, LPFMs, and NCE-FMs near TV6 stations already have this option. I've chosen to operate one of our translators vertical-only (using a Scala FMV folded dipole) for the following reasons:

1) The surrounding terrain is relatively flat and open, and our site is close enough to the COL to put at least 75 dBu across the city.

2) The tower we rent is heavily loaded, so it wasn't feasible to mount more than one bay.

3) To make licensed power with a single CP bay, the transmitter power would need to exceed 360 watts. But with vertical only, I can operate at 180 watts, and use a relatively inexpensive high-power exciter (Armstrong FMX-300B) as the transmitter.

4) I needed a slight amount of directivity to protect an adjacent channel station and the "off-the-shelf" FMV pattern fit the bill almost perfectly. The cost of this antenna was also very reasonable.

5) Vertical folded dipoles have sufficient bandwidth to allow combining of multiple transmitters within a 10 MHz range. (But don't try this with a Shively 6812!) We share our antenna with another translator for economic reasons, so this was another point in favor of installing an FMV. The wide bandwidth also reduces winter ice problems without resorting to de-icers or radomes.

 

[Shockwave]

I suppose the question that needs to be discussed is: Why doesn't the FCC allow full-service commercial FM stations the option to operate vertical only?

Horizontal linear polarization is legal, so why not vertical linear? The old "It shall be standard to employ horizontal polarization" rule was written in the 1940's, long before FM made its way into cars, and it needs to be reconsidered.

As I mentioned earlier in this thread, if money isn't a concern, I do understand the advantages of CP over linear polarization. However, some smaller stations on tight budgets could economize on power consumption if the horizontal component were eliminated and this would have little perceptible impact on signal coverage in many cases.

Of course translators, LPFMs, and NCE-FMs near TV6 stations already have this option. I've chosen to operate one of our translators vertical-only (using a Scala FMV folded dipole) for the following reasons:

1) The surrounding terrain is relatively flat and open, and our site is close enough to the COL to put at least 75 dBu across the city.

2) The tower we rent is heavily loaded, so it wasn't feasible to mount more than one bay.

3) To make licensed power with a single CP bay, the transmitter power would need to exceed 360 watts. But with vertical only, I can operate at 180 watts, and use a relatively inexpensive high-power exciter (Armstrong FMX-300B) as the transmitter.

4) I needed a slight amount of directivity to protect an adjacent channel station and the "off-the-shelf" FMV pattern fit the bill almost perfectly. The cost of this antenna was also very reasonable.

5) Vertical folded dipoles have sufficient bandwidth to allow combining of multiple transmitters within a 10 MHz range. (But don't try this with a Shively 6812!) We share our antenna with another translator for economic reasons, so this was another point in favor of installing an FMV. The wide bandwidth also reduces winter ice problems without resorting to de-icers or radomes.

Isn't it amazing how "in the field results" using VP can be so vastly different from some of the opinions expressed here?

 

[rfry]

Isn't it amazing how "in the field results" using VP can be so vastly different from some of the opinions expressed here?

The point that the c-pol antenna used by any given, licensed FM broadcast station in the US must radiate the same v-pol ERP as a v-pol-only antenna is a fact, not an opinion.

The FCC licenses FM stations for their ERP per polarization, not for their antenna gain per polarization. Stations may use whatever combination of antenna input power and antenna gain they wish, to produce that licensed ERP.

Therefore the field results for the v-pol coverage of these two configurations cannot be "so vastly different" if both configurations have the same radiation center height above the earth, use the same transmit site, and radiate the same v-pol ERP.

Of course, the FCC must specifically permit a station to use only v-pol, before the station may do so.

//

 

[RealityCheckr]

Isn't it amazing how "in the field results" using VP can be so vastly different from some of the opinions expressed here?

The point that the c-pol antenna used by any given, licensed FM broadcast station in the US must radiate the same v-pol ERP as a v-pol-only antenna is a fact, not an opinion.

The FCC licenses FM stations for their ERP per polarization, not for their antenna gain per polarization. Stations may use whatever combination of antenna input power and antenna gain they wish, to produce that licensed ERP.

Therefore the field results for the v-pol coverage of these two configurations cannot be "so vastly different" if both configurations have the same radiation center height above the earth, use the same transmit site, and radiate the same v-pol ERP.

Of course, the FCC must specifically permit a station to use only v-pol, before the station may do so.

//

Richard,
The reason this discussion is taking such an odd course is that it is about 90% certain that the original poster and at least one of the other respondents don't give a darn about the FCC because they are pirates.

This is why I asked what I did at the beginning - to expose the amateur/pirates in our midst.

To a pirate the most expensive thing they have is a transmitter of x watts. Since they want to reach the most people with that x watts the vertical antenna makes sense.

Their quoted vendor also knows that if the TX is at a fixed power that VP will outperform CP.

Now that we know the true motives of this thread it is probably time to drop it !!!

 

[rfry]

The reason this discussion is taking such an odd course is that it is about 90% certain that the original poster and at least one of the other respondents don't give a darn about the FCC because they are pirates.

That is as may be, but I don't have any provable basis either for believing or disbelieving such. Maybe you and/or others do.

The point of all of this that I wanted to bring forward is that for the same, single-bay transmit antenna radiation center above the earth and from the same transmit site, x watts of v-pol ERP produce the same v-pol field intensity at a given receive site whether radiated by a v-pol-only antenna, or by a c-pol antenna.

As such, the service areas of either configuration to v-pol receive systems should be identical.

IMO, this reality was not (publicly) recognized by some of the earlier posts in this thread.

//

 

[Chuck]

The point of all of this that I wanted to bring forward is that for the same, single-bay transmit antenna radiation center above the earth and from the same transmit site, x watts of v-pol ERP produce the same v-pol field intensity at a given receive site whether radiated by a v-pol-only antenna, or by a c-pol antenna.

As such, the service areas of either configuration to v-pol receive systems should be identical.

That is quite true. Since the FCC will let you run "X" number of watts horizontally, and the same power vertically, why wouldn't you do it? About the only reasons I can think of are to fit in a "shoehorn" location in the reserved band, or because your operation is outside of the bounds of FCC regulations. That could mean "pirate," but it could also mean "legal broadcaster" in another country. If you only have a 150-watt transmitter, then a vertical antenna with some gain might look pretty attractive to you. On the other hand if you were limited only by ERP, then circular polarization makes a lot more sense.

 

[Play Freebird]

Yes, pirates seem to prefer vertical polarization as it gives them the most bang for the buck, not to mention the antennas are easier to homebrew.

The following page with links to photos of European FM pirates has been mentioned before; some of the antennas are quite impressive:
http://www.klompenboer.nl/Impressies/Onder.htm

And how do you like the 'transmitter building' shown here:
http://www.klompenboer.nl/Piraten/2006-2007/Lachende Vagebond 02-02-2007/Index.htm

 

[Engineer]

I will say that I did find one pirate in Brooklyn with a two-bay circularly polarized antenna. However, every other one I've located has been vertical-only, and usually the Dominator-type antenna.

 

[ChiefEngineer]

I will say that I did find one pirate in Brooklyn with a two-bay circularly polarized antenna. However, every other one I've located has been vertical-only, and usually the Dominator-type antenna.

The dominator folks are prolific in indicating stations in the US are using their antennas but I've never been able to verify the supposed coverage or claims they make, or their gain figures.

The thread started with the dominator link. An African station uses their antenna! If thye could provide some verifiable information why not do so??