The best antenna for LPFM

[Koredump]

Hello all!

We are planning on upgrading our antenna system soon. At this time we are using two omb antennas with a power divider and a 1/2 inch transmission line. Someone recommended us ( ERI FM100A ) and someone else ( Jampro ). Since we have a 500 watt transmitter we are thinking of using one antenna.

Any thoughts?

Even though you may gripe a bit at first about the slightly higher price tag, you'll be patting yourself on the back years from now for buying the FM-100A. Tom Silliman never designed or sold a mediocre antenna...there are thousands of old Rototillers out there that have been out-performing their competitors for 30 years, and haven't changed as-built specs one iota.

 

[oldiesstation]

Good discussion here.I've installed the Shivley 6812.Good antenna,,but narrow bandwidth as was stated.But i don't know whether ERI sprinkles some kind of "Magic Dust" on their antennas,but they perform and are amazing.I would guess more commercial stations use ERI over any brand.Buy the ERI,you will be happy you spent alittle extra Good luck.

 

[littlejohn]

It's been a while, but if mempoy serves, the bandwidth discussion with one of the Sillimans noted, the larger diameter elements tend towards a wider bandwidth. The tradeoff is, they also lead to a greater chance for corona. Maybe one of their gurus will show up and confirm or deny my memory here... the conversation took place a long time ago. I had, but have lost over the years, a page and a half legal size of the proof Tom once wrote for me to explain how the design couples energy to free space. The bulk of the explanation was - and still is - over my head, the answer being 'real well'.
From a practical point of view, the E.R.I. antenna is often on the air when the other guy's isn't.

 

[TomT]

Narrow, pointy things attract lightning more than broad rounded things. Why lightning rods are pointy. So the tiny Shively would get lit up more than the ERI.

 

[bilco]

Ok what Am I missing here? People are talking about LPFM and referring to 300 watt and 500 watt transmitters. LPFM is limited to 100 watts ERP at 30 meters HAAT. A transmitter with that kind of power could feed a single bay antenna through lossy coax and still easily exceed that ERP limit. Why would someone want to pay the power bill for that when a 4 Bay ERI and good low loss coax, say 7/8ths to an antenna located at 30 Meters HAAT could be done with a 100 to 200 watt transmitter? Heck, a hombrew copper pipe J-pole and RG214 could probably do it with under 200 watts, though I haven't done the calcs for that combination. Of course I am assuming that these "LPFM" stations are running legally! Would those folks care to PM me with the Call signs for these statons?
Bill Croghan CPBE WBØKSW
Chief Engineer,
KOMP/KXPT/KENO/KBAD/KWWN/KWID
Lotus Broadcasting, Las Vegas, NV

 

[RadeoEngineer]

Ok what Am I missing here? People are talking about LPFM and referring to 300 watt and 500 watt transmitters. LPFM is limited to 100 watts ERP at 30 meters HAAT. A transmitter with that kind of power could feed a single bay antenna through lossy coax and still easily exceed that ERP limit. Why would someone want to pay the power bill for that when a 4 Bay ERI and good low loss coax, say 7/8ths to an antenna located at 30 Meters HAAT could be done with a 100 to 200 watt transmitter? Heck, a hombrew copper pipe J-pole and RG214 could probably do it with under 200 watts, though I haven't done the calcs for that combination. Of course I am assuming that these "LPFM" stations are running legally! Would those folks care to PM me with the Call signs for these statons?
Bill Croghan CPBE WBØKSW
Chief Engineer,
KOMP/KXPT/KENO/KBAD/KWWN/KWID
Lotus Broadcasting, Las Vegas, NV

You are clearly not familiar with the typical high quality engineering standards associated with LPFM installations.

 

[Goat Rodeo Cowboy]

Ok what Am I missing here? People are talking about LPFM and referring to 300 watt and 500 watt transmitters. LPFM is limited to 100 watts ERP at 30 meters HAAT.

Some of them may be in other countries where the rules are different. When you do web searches on LPFM, you get a lot of New Zeland links.

Other writers may be explaining what they know about antennas based on their experience with translators and satellites.

Does keep the conversation puzzling though.

 

[DudeFan]

Bilco,

LPFM can only used Certified, rather than type-accepted transmitters. The available units on the market that are certified are 30 watts exciters, 150 watt, and 300 watt units. Hence, you will hear alot about LPFM's running 300 watt transmitters loping at 100 watts or less. The difference in electricity consumption is negligible, but I'd rather have a 300 watts unit loping at less than half designed power than run a 150 watt unit almost full throttle, simply because it means greater longevity on the unit.

 

[necrat123]

Ok what Am I missing here? People are talking about LPFM and referring to 300 watt and 500 watt transmitters. LPFM is limited to 100 watts ERP at 30 meters HAAT.

Right but you know that many LPFMs run into single bay antennas. I have seen several that are using single bay circular antennas, and the calculated TPO is something along the lines of 250 watts. I think a lot of LPFMs were sold "packages" that had a 300watt transmitter, single bay antenna, and small feedline. As long as the transmitter is throttled to a TPO that gives you the 100w ERP, there is nothing illegal about having a 300 watt certified transmitter running at 250 watts if that's the calculated TPO.

I've visited easily 40 LPFM stations, and of the 40 or so, MAYBE 20% were using more than 1 bay. A few were using 2 bay half wave spaced antennas, 1 was using a 3 bay half wave spaced antenna. A couple were using these Comet CFM-95SL antennas (and you could tell, how bad the signal was on those!)

 

[TomT]

In the original question was stated that they were using a 500 watt transmitter & asking about what antenna would be best.

Unless they have an extremely long run for their feedline, 1/2" foam & a single bay would probably work just fine.
And would probably prove the most economical and reliable installation if a good quality antenna was purchased.
No inter-bay harness, for one thing.

 

[Kent T]

Those ERI antennas are superb and really perform for you. I have an over 30 year old Rototiller which still has held specification for all these years. I'd buy another ERI without even a second thought. Superb company who takes super care of their customers.

 

[joshzz]

We use a Shively antenna. We're quite happy with it.

What I would like to know has anyone ever conducted a study to find out which antenna reaches the greatest distance?

joshzz

 

[Goat Rodeo Cowboy]

What I would like to know has anyone ever conducted a study to find out which antenna reaches the greatest distance?

Are you looking for a study that would show that Brand A reaches a half mile further than Brand B under the same conditions and location?

I will leave the real nuts-and-bolts slide-rule-theory to people with the qualifications to do that. I worked for a company that makes the antennas that you see on top of cell phone towers. It was a small company so I had plenty of opportunity to bump into the "skink works" guys in the back who look for that "magic elixer" that will give you product some zing, some punch that your competitor does not have.

I worked in the department that supported our sales people. And they were always coming up with reports that Company C was making this claim in their sales presentation and Company D was making this other fabulous claim. "What do I tell my customers?" And the smartest, most brilliant engineer in the group routinely replied: "The laws of physics have not been repealed."

He would then sit the salesman down and explain: Here is the theoretical output we would get if we could design the perfect antenna and install it in the perfect location. And here is how close we get, and here is how close competitor A, B, C and D get. We're talking fractions of a percent in difference.

When you shop antenna brands, here is what distinguishes one manufacturer/designer from another: Customer Service. Durability and longevity. A way to tune and match local conditions and changes.

I would be much more concerned about the expertise of the people who as consultants select the antenna design (single bay vs multi-bay, bay spacing, etc.), the people who install the antenna, and the people who from time to time review or inspect the antenna to make sure it hasn't broken, bent, corroded or otherwise lost effectiveness.

The idea that Brand A antenna might expand you coverage an extra mile over Brand B is probably not the issue to lose sleep over. Worry about the guy who looks at the hills or lack of hills in your terrain and starts advising single-bay vs. multi-bay, half-wave spacing vs wave-length spacing, etc. That person will have much, much more to do with you coverage that the antenna brand.

Antenna brand could mean your antenna works for 15 years instead of 4-1/2 years before replacement.

 

[Play Freebird]

Those ERI antennas are superb and really perform for you. I have an over 30 year old Rototiller which still has held specification for all these years. I'd buy another ERI without even a second thought. Superb company who takes super care of their customers.

How do we usually evaluate coverage of our stations? We take a drive.

Perhaps the Rototiller design performs well with mobile receivers because it apparently favors vertical polarization over horizontal. Here's a NEC model showing the ratio of an unmounted ERI antenna in free space; note that the vertical relative field (in blue) exceeds the horizontal (red - the plot has a typo) at nearly every azimuth:

http://www.kyes.com/antenna/gnec/rot1p.html

Most "rimshotters" understand that, when side-mounted on a tower, the vertical "gain" in a favored direction increases even more, as shown in the lower examples:

http://www.kyes.com/antenna/gnec/gnec.html

The FCC assumes the axial ratio of a CP antenna to be unity, but for many years I've suspected that the Rototiller has an exceptional advantage in the vertical polarization, and this study appears to confirm my thoughts.

 

[rfry]

Perhaps the Rototiller design performs well with mobile receivers because it apparently favors vertical polarization over horizontal. Here's a NEC model showing the ratio of an unmounted ERI antenna in free space; note that the vertical relative field (in blue) exceeds the horizontal (red - the plot has a typo) at nearly every azimuth: ...

The correlation of NEC modeling with the real world depends greatly on the integrity of the NEC model with respect to the "rules" of NEC, which in turn are based on the skills, experience and inputs of the analyst.

For another NEC calculation of the patterns of the ERI rototiller, please refer to paper 6 at http://rfry.org . Figure 4 in that paper shows the H&V radiation patterns for a 2-bay rototiller array in free space, compared to those when it is face-mounted on a 24" face triangular tower section.

The circularity of both sets of patterns there is much better than shown in the pattern links posted earlier in this thread.

ERI will provide potential customers with gratis, typical, measured patterns for most of their antenna elements when face or leg mounted on towers of various widths, at a frequency on, or near that of the inquiry.

RF

 

[necrat123]

I have found that if you ask engineers what kind of antenna they like, it is the same as asking a regular guy what kind of car they like. You have Chevy guys, you have Ford guys. You have guys who like Chevys and respect fords. It's the same with antennas. You have ERI guys, you have Dielectric guys, you have Shively guys. So much of it is based on personal opinion, you will never get a really straight answer.

Let's face it. ERI, Jampro, Shively and Dielectric all make good antennas. There are 1000's of them out there, performing day in and day out, working hard. As long as you stay away from knockoff brands and no names, you will probably do fine.

I've installed Shively's on the jobs I've done, and had good luck with them. I see more ERIs than anything else out there, so that should say something about ERIs. I know the guys at Shively personally, they're a great group of people there. I only know one person at ERI, but he's also a fantastic person as well. Good luck with your project!

 

[RadeoEngineer]

ERI gets about 85% of the domestic business and Jampro gets about 85% of the international business. There's no difference between the two, except ERI is known for the rototiller (which Jampro also makes) and Jampro is known for the Penetrator (which ERI also has a version). They're still the only two that can do a full size range test of an antenna design, and that's important.

 

[joshzz]

We like our Shively antenna. Fantastic Customer/Tech support and very affordable.

 

[Play Freebird]

The correlation of NEC modeling with the real world depends greatly on the integrity of the NEC model with respect to the "rules" of NEC, which in turn are based on the skills, experience and inputs of the analyst.

For another NEC calculation of the patterns of the ERI rototiller, please refer to paper 6 at http://rfry.org . Figure 4 in that paper shows the H&V radiation patterns for a 2-bay rototiller array in free space, compared to those when it is face-mounted on a 24" face triangular tower section.

Interesting paper -- however, your plots use a dB scale (5 dB per division) rather than the relative field scale as used in the link I posted, which tends to make the pattern circularity appear better. For example, in your Figure 4, the maximum Vpol value at around 290 deg is +5.5 and the minimum at 150 deg is about -6.5, so the max/min ratio is about 12 dB. This compares closely with the "20 inch removed" link from the kyes.com site (when rotated 180 degrees to account for antenna placement in the model).

Your NEC model also confirms that the RMS of the vertically-polarized component ("loops only" in red) exceeds that of the horizontal component ("loops only" in blue), which is the main point I want to make about ERI Rototillers. Based on your modelling, wouldn't you agree that the V/H RMS ratio is 2 to 3 dB greater than unity, and that this might account for better mobile coverage performance? Personally, I think it's a good thing.

 

[littlejohn]

Some good points made here. I still maintain, however, wghen mine is on the air and thother guy's isn't, I got the better antenna. I have been on both sides of that situation over the years, the ERI product has never put me there, so I use it when the choice is mine.