Management ignored me when I suggested LPFM....

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kc8gpd
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Re: Management ignored me when I suggested LPFM....

Post by kc8gpd » Mon Mar 12, 2018 10:29 am

yes they had older electrical grids where the signal followed along the neutral lines for about 4 miles leaking off the lines along the way. I also think the local qrm at their frequency was not too bad either.

also these towns were small city like where there was not more than 500ft between rows of power polls running the alleys.

I can say one of the towns was Casper WY (due to illness I believe he is no longer running the station) and he was visited by a now retired fcc agent john spruage. think i spelled his last name right. he was a highly regarded field agent by the industry here in the Denver area.

but anyway my point is when neutral loaded carrier current works, it works great. the reasoning for neutral loading is that very often even older electrical grids have filters on the transformers that stop your signal dead cold at the first pole pig it hits. neutral loading often will bypass this blocking. the key is above ground wiring and continuous neutrals through out the area. my situation is an example of when carrier current does not work so well due to underground wiring and my suspicion is the neutrals are not setup in a way conducive to long distant RF carriage, but it serves my needs which is to cover the apartment complex I live in.

also if you use a frequency below 1600 you can get away with a cheaper used nems Clarke 120E FIM calibrated against a fim 41 for measurements, and I recommend low to mid band depending on where the local qrm level is the least. the lower frequencies tend to radiate less off the lines and the FCC rules for 15.221 that deep thought quoted show that more liberal field strengths are permitted the lower you go in the band. for instance at around 530 you would be permitted to radiate 15uV/m out to about 88 meters where as at 1700 you would be allowed to radiate out to only a distance of about 28 meters from the line. so at the low end of the band you would be permitted to shove more power into the line before reaching the field strength limits set out in 221 which would equate to a little more range, but the down side to the lower end of the band is more sky wave and local qrm. I would try and avoid the X-Band often the lines are a better match to the power lines and the signal radiates more easily and with less loading.

I recommend picking up an old lpb tcu-30 and me personally would get one of those greek made 0-20 watt agile dds transmitters they are very clean spectrally to begin with are adjustable, cost about the same as a used rockbound lpb am tx, and you shouldn't need more than 10 watts to reach the allowed leakage levels per 221 and often will require only a couple watts.

I hope my rambling explanation gives you more insight into the inner workings of part 15 carrier current.

edit: here is a couple carrier current tutorials written up by a broadcast engineer,,,

Carrier Current 101 Pt. 1
http://krocksradioone.com/forum/index.p ... ,64.0.html

Carrier Current 101 Pt. 2
http://krocksradioone.com/forum/index.p ... ,96.0.html
kc8gpd

"The scientists of today think deeply instead of clearly. One must be sane to think clearly, but one can think deeply and be quite insane."

spareparts
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Re: Management ignored me when I suggested LPFM....

Post by spareparts » Thu Mar 15, 2018 5:07 am

Lots of good info re carrier current - will throw this out there as it's likely relevant to the loaded neutral suggestions:

Facility buys it's power in bulk, delivered on overhead three phase at 13.2 kV. It's stepped down on site to 4160 V, and from there, stepped down again to 120/208 three phase.

Per code, the neutrals for the 120/208 V systems are solidly grounded at the transformers.

kc8gpd
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Re: Management ignored me when I suggested LPFM....

Post by kc8gpd » Thu Mar 15, 2018 7:55 am

i'm not sure how that would effect carrier current operation maybe one of the RF experts here could, but you state it's code to have them solidly grounded at the transformer and apparently neutral loading passes transformer and these guys experiments that seem to work pretty well would suggest that it has very low significance on the operation of neutral loaded carrier current. i bet "@deep thought" could answer that question. maybe he will chime in again.
kc8gpd

"The scientists of today think deeply instead of clearly. One must be sane to think clearly, but one can think deeply and be quite insane."

WREN
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Re: Management ignored me when I suggested LPFM....

Post by WREN » Wed Apr 18, 2018 10:41 pm

There will probably be another LPFM filing in the future. I've seen 2023 as one thought although that is speculation. First the FCC will need to make sure that the top five or six groups own almost everything! Your group should have filed in 2013, of course. An LPFM signal can cover a small to medium size city competently if it is on a clean channel and is built properly. I run one of a group of four independent station that share studio space and a diplexed antenna. We all run competitive formats and do have listeners. Most actually have a net positive income. Info on our group is at http://www.RadioCoop.org.

For LPFM information, you should go to http://www.RecNet.com and https://www.prometheusradio.org. These are the primary LPFM websites. Rec Net is engineering oriented wherea prometheus is more of a site aimed at setting up 'artsy' stations but both have value and news updates.

LPFM isn't perfect but it can be 'real radio' if run properly. You must have a real format!! Oddly finding good volunteers has not been that hard even if you aren't allowing them to come in with their own stack of records to play. We do stream with good audio. That is important but it is also of value to have whatever FM signal coverage that you can get. I don't see Part 15 being of much value at all save for a true hobby station for a small neighborhood and I'm not at all sure of that value.

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Dale H. Cook
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Re: Management ignored me when I suggested LPFM....

Post by Dale H. Cook » Thu Apr 19, 2018 7:08 am

For those of you who don't know who "WREN" is, he is Jon Hall, a highly experienced radio engineer based in Charlottesville, VA, whom I have known for about twenty years. He is now also heavily involved in LPFM. Welcome aboard, Jon!
Dale H. Cook, Contract Engineer, Roanoke/Lynchburg, VA
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Bill DeFelice
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Re: Management ignored me when I suggested LPFM....

Post by Bill DeFelice » Fri Apr 20, 2018 3:43 pm

Dale H. Cook wrote:
Thu Apr 19, 2018 7:08 am
For those of you who don't know who "WREN" is, he is Jon Hall, a highly experienced radio engineer based in Charlottesville, VA, whom I have known for about twenty years. He is now also heavily involved in LPFM. Welcome aboard, Jon!
Dale, any relation to Hall Electronics? If so I remember dealing with Jon for some station projects I worked on. Good times.
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Dale H. Cook
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Re: Management ignored me when I suggested LPFM....

Post by Dale H. Cook » Sat Apr 21, 2018 6:00 am

Bill DeFelice wrote:
Fri Apr 20, 2018 3:43 pm
Dale, any relation to Hall Electronics?
Bill -
The one and the same.
Dale H. Cook, Contract Engineer, Roanoke/Lynchburg, VA
http://plymouthcolony.net/starcityeng/index.html

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