LPFM to HD upgrade

I'm a high school teacher (I'm certainly not an engineer) in charge of an LPFM I set up for our students. We've been on the air for a little over 2 years.

The students have done a great job! Now they want to do some upgrading to experiment with HD Radio technology. GREAT... I love a challenge but HD LPFM?!?!


I'm hoping an engineer with a kind heart will take pity on me and tell me if I'm close to the mark here.

We currently have a single bay Jampro JLCP and with our feed line all told, we have a TPO of 274 watts out of a Nautel VS300.

My goal is -14dB injection and the VS300 doesn't have enough headroom to handle the increased demand (including the expanded mp3 mode) unless i make a change to the antenna. My thought is to go to a two bay JLCP half-spaced (we can handle that space) -- bringing the TPO requirement to 202 watts. The vs300 can handle 217 watts under these conditions.

There doesn't seem to be any documentation for LPFM HD -- maybe because there aren't any as yet, but I would have to assume perhaps there may be some translators somewhere doing the low power HD thing.

Any thought's would be greatly appreciated, but remember, I'm a music teacher

Ralph

To my knowledge (which may be incomplete!), there are zero LPFM stations operating in HD. I'm also not aware of any translators which originate HD programs.

For LPFMs, I'm not sure there is any HD equipment which is LPFM certified, so you may not be able to do this at all.

I think you're right in that I haven't seen any sign of anyone doing it at any low power facility. mostly because of the early -20dB power level restriction i would suspect. but the new level increases are interesting.

The vs300 is compatible with HD Radio and it's LPFM certified, I would imagine they were thinking translators (many that use the VS series) might take them up on it. Not sure what to think

Raloh.... I PM'd you...

thanks for the note, oldie919

I do see a lot of chatter on the internet about translators rebroadcasting HD2's in analog -- nice little work-around loophole for the primary stations I'd say

But no chatter about actually broadcasting digital HD Radio for LPFM or any low power application. People seem to have been thinking about it, but not actually doing it.

Ralph Martin said:

But no chatter about actually broadcasting digital HD Radio for LPFM or any low power application. People seem to have been thinking about it, but not actually doing it.

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Possibly because of the royalties that must be paid to iBiquity or whatever it is these days...I don't think non-comms can plead poverty on that one. Make sure you take that into consideration...it can make a cheap operation more costly.

Radio-X

It seems they're trying to make it a bit more affordable for LPFM and other noncoms. We'll see how it turns out.

If everyone in the industry is serious about eventual digital conversion they're going to have to include the noncoms, translators, LPFM --- everyone. For our station, the only way we'll be able to do it is through the support of those in the industry, our local community and our amazing students.

Not to mention the great talent of those experienced engineers out there who may have remembered the spark of enthusiasm they received working in their high school, college or community radio station.

At one time, there was a LPFM running HD, but I don't think it worked out well for them.

I suspect you will find the coverage from a HD signal will not be worth the cost. The usable signal will be considerably less than your analog signal. By the time you you pay for the Ibiquity licence and the required equipment to generate the HD signal, And a new antenna, you may come to the conclusion that it simply isn't worth it. But then, maybe you have an open checkbook. Most schools don't.

Why not give Nautel a call to see what they think you need to to buy? That seems like a good place to start.

I get the cost -- and I know what I need in terms of the importer and exporter and Nautel has been very upfront with what i need in terms of cost... they're great!! I'm a BIG Nautel fan! I've also been preparing for the cost for licencing through DTS and it is significantly better for noncoms and even better yet for LPFM if you consider multicasting.

I have a community that's been very supportive; the students work tirelessly; the parents volunteer and I still have my health to give it all I've got; so this is definitely the time. And looking long term with the problems radio faces in high school and college you need to upgrade while the support is hot! I'd rather do "exciting new technology" projects than "save our station" drives.

And the lucky students on the ground floor get to learn about antenna system design; digital multiplexing the list goes on and on. Plus down the road, I'd like to know that when radio stations face either going digital or going out, they 'll just have to "flip a switch" and they're good to go

The point you make about the signal coverage is certainly a good one and is why I'm asking the same thing. When the restriction was at -20dB it wouldn't make sense for LPFM stations, but the new -10dB rules for digital -- that's very different. Even -14dB should be enough to do the job (unless I'm missing something). Then I was surprised that there was not more interest or experimentation at the new power levels in low power facilities.

Are there any noncom class A's running HD?

Ralph Martin said:

Are there any noncom class A's running HD?

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Yes, WSOU and WKCR are two college-owned stations that cover the New York metro pretty well. Their HD signals do a decent job. Both of them use HD-2 subchannels. Even though their HD signal only has half the range of their FM signal, one cost-effective approach to this is they can stream their HD-2 channels.

Oh my, our 60 dbu contour covers about 93,000 people
Thats LPFM for you Sounds like we're gonna have a really good time with this.

As mentioned, you may want to consult with Nautel, but in theory, as long as your transmitter/Power Amplifier is wideband enough and with enough headroom, you could probably low-level combine the analog and HD into a single amplifier/transmitter. You would have to add some pretty steep RF filters on the output, and replace your existing antenna with a high quality commercial broadband antenna. The station would have to also purchase and install the more expensive exciter, exporter, and pay Ibiquity fees. No matter what your class of station, HD is a steep capital expense.

There are several possible methods for producing an HD signal. One is low level combining which has already been covered pretty well. An alternative is to use an HD transmitter to feed a separate antenna. Sometimes, this is more cost effective, depending upon your circumstances.

Something also to think about is that LPFM stations can own up to two translators. One or both could rebroadcast HD signals, thus expanding the program offerings of the LPFM.

I did get lots of good info from Nautel. We can do it from the transmitter and their exciter importer and exporter is ready made for the transmitter we have. I already have the quotes and set as far as that. The transmitter is adjacent to our studio, so no STL concerns. The need for added RF filter is new to me (thank you).

The problems as I see it, from a novice perspective, is the TPO headroom isn't there for a single bay antenna. The antenna is also very narrow band so real changes will have to made there and two bays will be needed. Jampro is another great bunch of folks they're setting up the antenna system to be HD friendly.

This juuuust might work

I guess I should add: The whole antenna system has to fit on a 2" pipe mast on our roof. So we're fairly limited as to space. We can have a 1/2 spaced two bay with a low physical profile -- no tower -- this is LPFM all the way

Ralph Martin said:

The antenna is also very narrow band so real changes will have to made there and two bays will be needed. Jampro is another great bunch of folks they're setting up the antenna system to be HD friendly.

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Some antenna designs are more narrow than others. For example, the common "ring-stub" antenna is setup for the specific frequency and being off the channel by more than a few hundred kHz will start to see reflected power. Ring-stubs should to be wide enough to handle HD, too, but might not be optimum. A more wide-banded approach is the "double-V" design favored by Jampro, PSI, Nicom and others. I have personally loaded a 103.3 tuned antenna with a 105.7 transmitter and only had 2-3W reflected for 250 forward. Because the double-V antenna tends to be more than a mHz wide, it can easily handle HD. Even broader are the "rototiller" designs like those made famous by ERI.

Thanks for that, Kmagrill -- I'm sure you're right, but I hope I can get the JLCPs to work because they have such low wind drag and the mast can't be guyed. But, alas; physics is physics...

I'm going to miss the single bay match we get. It's so good that I'm sceptical of the readings (less than 1 watt reflected with 274 forward). That's of course, unless a good sized bird decides to sit on the antenna for a little rest and ruin the match enough to cause a power foldback. Caught the big guy landing and sure enough, I get a SWR power foldback alarm on my phone. He takes off and everything's back the normal. I'm told a 2-bay won't be so affected by birds. Wow! Something to look forward to already

Ralph Martin said:

I'm going to miss the single bay match we get. It's so good that I'm sceptical of the readings (less than 1 watt reflected with 274 forward).

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It would be pretty minimal (relative to the overall cost of the VSHD and Exporter/Importer) to just replace the VS300 with a VS1 and keep the 300 for backup. That would also give you lots of headroom for higher injection levels, so that HD coverage comes closer to analog coverage and wouldn't require the antenna change, as well as adding some redundancy to your chain. Gain between a single bay and two bay halfwave is pretty minimal, so the VS300 is going to be extremely restricted in what injection level it can provide anyway (seems I recall seeing 27x watts TPO earlier in the thread?).

Just some thoughts, as I catch up on a couple months worth of traffic.

RF_Warrior said:

It would be pretty minimal (relative to the overall cost of the VSHD and Exporter/Importer) to just replace the VS300 with a VS1 and keep the 300 for backup. That would also give you lots of headroom for higher injection levels, so that HD coverage comes closer to analog coverage and wouldn't require the antenna change, as well as adding some redundancy to your chain. Gain between a single bay and two bay halfwave is pretty minimal, so the VS300 is going to be extremely restricted in what injection level it can provide anyway (seems I recall seeing 27x watts TPO earlier in the thread?).

Just some thoughts, as I catch up on a couple months worth of traffic.

Click to expand...

Is the VS-1 certified for LPFM use?

Unfortunately the vs1 isn't LPFM certified -- only their vs300, so we're limited in that way. The good thing is that the cost of adding a second element won't be much because we just have in on a mast. It just requires the purchase of the antenna and combiner... oh, and a good a-frame ladder. That, I hope will bring the TPO needed down to 170 watts. With a single bay, I might be able to get -18dBc that won't do it for us. My goal is -14dBc. With a vs300, I'm gonna need a 2-bay and their "power-boost" addition.

My big challenge right now is making sure the antenna system will tune wide enough (200kHz each side). Jampro is still working out the details for me. I should know more this week.