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The best antenna for LPFM

F

fl-lpfm

Guest
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?
 
This might not be real scientific but it's been my experience that all things being equal, you get the best coverage with a single bay circularly polarized antenna perferably mounted on a pole as opposed to the side of a tower or other structure.

If you can't afford circular polization then the next best is verticle. I'm not sure if they allow that on LPFM on commercial channels. They do on noncoms below 92.1 but not commercials without special authority. As you add more bays you tend to bend the signal more as a light house would and you can actually shift alot of the strength up over the horizon instead of downward where the listeners are. If it's a call between a bigger ( more bays ) antenna or a stronger transmitter, buy the stronger transmitter and keep the number of bays down.
 
fl-lpfm said:
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.
Click to expand...

Keep in mind that should you change the type of antenna you use (i.e. switching to a single-bay), you will be required to file another Form 318 and a Form 319 when the installation is completed. This would be a minor modification to your authorization.
 
CaptBob92 said:
This might not be real scientific but it's been my experience that all things being equal, you get the best coverage with a single bay circularly polarized antenna perferably mounted on a pole as opposed to the side of a tower or other structure.

If you can't afford circular polization then the next best is verticle. I'm not sure if they allow that on LPFM on commercial channels. They do on noncoms below 92.1 but not commercials without special authority. As you add more bays you tend to bend the signal more as a light house would and you can actually shift alot of the strength up over the horizon instead of downward where the listeners are. If it's a call between a bigger ( more bays ) antenna or a stronger transmitter, buy the stronger transmitter and keep the number of bays down.
Click to expand...

Thank you very much.
 
PA_Tune said:
Keep in mind that should you change the type of antenna you use (i.e. switching to a single-bay), you will be required to file another Form 318 and a Form 319 when the installation is completed. This would be a minor modification to your authorization.
Click to expand...

This is part of the change since we are doing height adjustment. We wanted to take this opportunity for the upgrade.
radiovigilante said:
Go with the ERI have tried several and in our case the ERI is the best.
Click to expand...

Thanks.
 
Hang the ERI. 20 years from now, have someone go up and make sure it's still mounted solidly for the next 20 years. Sleep soundly.
 
Thank you all for the help. Now, what about the transmission line? Should we stay with the 1/2 inch or should we upgrade to a 7/8?
 
CaptBob92 said:
This might not be real scientific but it's been my experience that all things being equal, you get the best coverage with a single bay circularly polarized antenna perferably mounted on a pole as opposed to the side of a tower or other structure.

If you can't afford circular polization then the next best is verticle. I'm not sure if they allow that on LPFM on commercial channels. They do on noncoms below 92.1 but not commercials without special authority. As you add more bays you tend to bend the signal more as a light house would and you can actually shift alot of the strength up over the horizon instead of downward where the listeners are. If it's a call between a bigger ( more bays ) antenna or a stronger transmitter, buy the stronger transmitter and keep the number of bays down.
Click to expand...

One more thing... Our antenna is mounted to a mono pole.
 
Not sure that 7/8th is worth the extra expense here.

Don't have the specs on your situation, but I assumed antenna 100 ft. AGL, single CP bay with a gain of .46.

If you used 125 feet of 1/2" foam, your TPO would have to be about 263 watts. If you used the same length of 7/8" foam coax, your TPO would have to be about 241 watts. With a 250 watt transmitter, this would be an issue. However, not much point to spend extra for 7/8th coax where you have a 500 watt transmitter to make up the difference.

Have an earlier version of the ERI 100 series on a 900 watt non-com (4 bay,fed by 500 watt transmitter); works quite well--however different design than the current model, which resembles the Jampro designs.

Have used the SWR antenna on several translators, and this antenna also works well. It is ruggedly built also.
 
In my experience, nothing exceeds ERI...and I do not know why...that is just how it is in my world...Cheers..JBI
 
I second Jboyd. When we went shopping for a new antenna, the same model of SWR that we have would have been over $1k more than what we got the ERI for. In fact the ERI came in less expensive than a number of others.
 
I am sure that could be true...but my evaluation is based totally on the coverage that I have experiencd with ERI in the past...your comment reinforces the wisdom of the purchase...Thanks....
JBI
 
Thank you all for your feedback! ERI keeps the top spot on almost everyone list. I think what we are going to do is go with one bay setup and puch more power to get our ERP. We hope that we can get better coverage from ERI compare to our OMB antennas.
 
Hello to all

We also are in need of a new antenna and we also are a low power fm with 300watts right now cause the other transmitter burned out :) and we currently use a linear pll fr broadcast but may i ask you where can we find the eri antennas you propose i searched with google with no luck (We are from greece) ?

Does also anybody know anything about prices aproximatelly ???


Thanks
 
djsakisd said:
Hello to all

We also are in need of a new antenna and we also are a low power fm with 300watts right now cause the other transmitter burned out :) and we currently use a linear pll fr broadcast but may i ask you where can we find the eri antennas you propose i searched with google with no luck (We are from greece) ?

Does also anybody know anything about prices aproximatelly ???
Click to expand...

The spec sheet for ERI's current LPFM antenna is here:

http://www.eriinc.com/pubs/20090317005_AEN01w.pdf

This product is based on the widely-imitated "double-V" design, patented by Peter Onnigian of Jampro in the late 1960s. Note that a choice of Type N or 7-16 DIN connectors is available from ERI.

ERI used to sell a low-power non-pressurized "Rototiller", but I think that product has been discontinued. However, the low power model employs an external shunt feed to the elements, rather than the internal feed -- which, in my opinion, is one of the primary advantages of the "Rototiller" design.

There are a number of "double-V" LPFM antennas on the market. This is a classic design for circular polarization, a good tradeoff between size, bandwidth, and manufacturing complexity. Jampro and SWR products are very similar in construction; here's the Jampro JLLP info:

http://www.jampro.com/index.php?page=jllp-low-power-fm-antenna

Personally, I prefer PSI's low power "slant V", with thicker elements that are less affected by ice build-up. (PSI can provide de-icing heaters on request.) These are non-pressurized with a choice of Type N or 7/8 EIA connector, but be aware that the end caps are welded and not adjustable in the field:

http://www.psibroadcast.com/antenna-fm.asp#fml

If you are forced to minimize weight and windload, the Shively 6812B is probably the best compromise (its dead weight for a single bay is only 1.4 kg) -- but it is a narrow bandwidth (high-Q) design and will not tolerate much ice before going so far out of tune that your transmitter will become unhappy.

http://www.shively.com/ds-6812b-fw.php

For some examples of installations where the 6812 is used, see:

http://www.necrat.us/wjzflp.html

http://www.necrat.us/wbcrlp_pro.html


I see that Shively has introduced a double-V design, the 6832, with much greater bandwidth:

http://www.shively.com/ds-6832.php


Armstrong Transmitter, near Syracuse, NY, also sells an LPFM antenna which works reasonably well. Here's a photo of an installation:

http://www.necrat.us/wrrslp_pro.html
 
We have the apparently now-discontinued "Rototiller" version the the FM100. It is an excellent antenna. Our SWR is a slant-v. The SWR is perfectly acceptable. The ERI, for whatever reason, is an awesome performer. I have wondered why the discontinued it. Judging from the pictures, it looks like it may have been cost reasons. The newer FM100s look like they are steel, rather than the brass that the rototiller version uses.
 
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