Gas or no Gas

[TomT]

This thread has gotten a little confused but here's the bottom line:

1. With an April 15th deadline you don't have time to mess around. The FCC does not grant extensions because you thought you came up with a better plan at the last minute.

2. Order your antenna NOW. You will be lucky to get it in time.

3. Order your feedline NOW. A little better margin, but still getting late. If, as originally set forth, the ERP is 3500 watts and you have a 3 kw transmitter, 7/8th will work. If it's 5400 watts, then you need 1 5/8th air. Don't mess around with the foam.

4. You also should have the transmitter in house as well.

You are really out of time, unless you are in the south and in the desert. You can't count on the spring weather to give you enough window to get that antenna up. Then there is the problem of lining up tower climbers.

Move.

 

[Kmagrill]

Well, we haven't firmly decided on a strategy yet. We may still go with a 2-bay antenna system. But we'll have to add an extension on the tower for that. I'd like to get 3 dBd gain, if possible. But time is running out so we will need to make a decision before the week is out.

A rule of thumb for most antenna elements is a gain of about 0.5 per bay, assuming the elements are fully spaced. So, a 2 bay antenna has approximately unity gain. A four bay antenna has a gain of 2 and so on. There are a lot of odd antenna designs with smaller apertures (shorter bay spacing), but these all have less gain than fully spaced elements. To put it another way, you'll need about 12kW TPO for a 1 bay, 6kW TPO for a 2 bay, 4.5kW TPO for a 3 bay or 3kW TPO for a four bay. Those are estimates based on 90% line efficiency and approximate antenna gains. Your actual mileage will vary depending on the line type and length as well as the antenna type.

You do have the option of going on the air with less than optimum ERP and/or HAAT. If you have a 3kW transmitter and a 1 or 2 bay antenna, you can modify your CP to specify lower power. As long as your 70dBu city grade signal covers the city of license, you can request whatever you want as long as you have at least 100W at 30 meters HAAT or equiv.

You can also specify a lower center of radiation rather than try to extend the tower height. If your antenna needs to be 4 bays, you still might put the top bay at the same height above ground, but then the center of radiation would move down about 3 meters (between bays 2 and 3 instead of between 1 and 2), requiring you to file a CP mod. That would be cheaper than trying to add a section to the tower.

Even if you put up a 1 bay antenna at 200 feet and run a few hundred Watts, you're going to be legal as long as you:

A. Cover at least 80% of the community of license with a 70dBu signal and
B. Get a CP from the FCC for whatever you're going to do.



If you haven't done this stuff before, it may be time to consult with a local engineer that has. There are a lot of potential pitfalls that can happen to a new installation. With time being short, any mis-steps could cost you your license.

Your time is very short, so you need to make your decisions now and order your parts and line up your tower crew.

 

[Engineer]

And to make things worse... your time window runs right across NAB at the beginning of April. You can't get anything done at all during NAB. Everything stops. You can't get equipment as vendors and manufacturers are away the week before getting set up for the show.

You need to have everything on site as fast as possible or this will not get done. Don't let the perfect be the enemy of the good. Get the station on the air in compliance with its permit by any means possible.

 

[oldiesstation]

Do you have any buildings nearby that are 100 ft high? Or just erect a quick 100 ft and go for the minimum class A 100 watts,30 meters.You never mentioned the city,but this should cover 80% with a 70 dbu.You don;t have time to spare. I saved a local university's cp this way.Got it on air the day before the cp expired.That was way too close..

 

[Carmine5]

Here's what happened: the owner of the CP, who got it at auction, kept dithering as to what to do about it. He put it up for sale at one point but, as is often the case, wanted too much and got no takers. In the meantime, we kept urging him to build the station. Why he didn't we still don't know.

Last month the owner threw up his hands and said he was going to let the CP expire. So, myself and a couple of other guys are trying desperately to come up with a plan to save it. We know we are just about out of time. The other problem is the tower site, there is not really enough space to put up decent antenna array. There's enough space for a single antenna.

The question about using gas came up because of some conflicting advice we got from an engineer and a station owner (who is the one offering to diplex with us). One said use foam, the other said use air pressure.

The idea now, as many of you are saying, is to do anything to get it on the air. And you've provided some great suggestions for which I thank you. As I said we will come up with the plan by March 1. I forgot about the NAB Show.

Funny, but I really wasn't planning on building an FM station at all but was getting ready to build an LPTV station.

 

[WNTIRadio]

Put up a single bay for now and get it on the air. You can buy a bigger tx later to increase TPO later on.

Whatever you do, build it! Don't let it expire.

 

[Kmagrill]

Do you have any buildings nearby that are 100 ft high? Or just erect a quick 100 ft and go for the minimum class A 100 watts,30 meters.You never mentioned the city,but this should cover 80% with a 70 dbu.You don;t have time to spare. I saved a local university's cp this way.Got it on air the day before the cp expired.That was way too close..

We've done this as well and it can save your CP. If the tower is problematic, you would be well advised to take the path above. You can use any structure that meets the minimum class A spacing rules and provides the requisite 70dBu coverage. We once hung a single bay on a 20' mast out the top of a very tall tree, for about a year, to keep a station from going dark when it lost its tower lease. The antenna was just over 100' AGL and it actually covered the town rather nicely. The station traded announcements to the host business rather than pay rent. I currently co-own one that is authorized for 105W from the roof of an office building in a small town for the same reason.

In addition to showing that the spacing requiremnts of 73.207 are met, your consulting engineer also will have to show that human exposure meets the safety limits from whatever you propose. This may be a limiting factor in power if the antenna is low to the ground, however more than 100W should be possible almost anywhere.

 

[TomT]

OK---is there space for the originally proposed 3 bay antenna? Without all this blather about diplexing, etc, etc.

If so, put the antenna up, put the feedline up turn on the transmitter & send in the 302 before April 15. Even if you have to run the transmitter off a geni, sign on from a cassette machine, run the national anthem, iron butterfly to 17 minutes & sign-off.

There's no time to file for anything--Commission won't act in less than 45 days any.

Once you have the 302 in hand then file for modification. The station license is "alive," and if you have to shut down after a few days you can file an STA (The dog ate my transmitter), while you wait for a new permit at a different site. This would be a minor modification and would take about 60 days to process.

 

[Kmagrill]

When we were at risk of losing a license due to being dark, we got a CP mod in slightly over 2 weeks when we asked nicely and explained the circumstances. This was within the last 3 months, so the FCC is responsive if there's a good reason to be.

However, if you are able build the facility as it is on your permit, that's usually going to be the fastest approach.

Find yourself a good local engineer to help you get this under control. You have a lot of variables and unknowns that you really need to sort out right away (like before this Friday). You have seen that there are many ways to handle these situations. All of them are viable, but a direction needs to be taken and advanced without looking back. Dithering will delay you and potentially cost you your license.

To muddy the waters further, here's another possible option:
Since you are the new owner of the CP, there is a chance that you can ask for an extension of the CP. Although an extension is normally not granted, new owners can sometimes ask for an 18 month extension, but I think you have to allow at least 90 days for processing, which you probably don't have. That's a question for a very good FCC attorney.

 

[Carmine5]

To muddy the waters further, here's another possible option:
Since you are the new owner of the CP, there is a chance that you can ask for an extension of the CP. Although an extension is normally not granted, new owners can sometimes ask for an 18 month extension, but I think you have to allow at least 90 days for processing, which you probably don't have. That's a question for a very good FCC attorney.

I actually tried that. But according to Irene Bleiweiss at the FCC, the Commission, by way of a court ruling, is no longer allowed to do that. No extensions for new owners.

The other problem, which may explain why this CP has not been built, is that it calls for an antenna height that would require a 30' extension on the existing tower (and moving a strobe light). Neither the coastal commission nor the county would permit the extension.

But I think I will follow TomT's (and other's) approach and just get the damn thing built anyway possible.

 

[Kmagrill]

If you can't extend the tower, you need to apply for a CP mod anyway. Find a location on the existing tower or pick a new site and put in your 301 ASAP.

 

[TomT]

Build it, file a 302, and explain the lower height on the tower due to tower loading considerations, or some such. Unless the tower is really far out from the city of license, even 50' feet lower should still provide city of license 70 dbu coverage. Keep to the original stated ERP.

Then file a 301 to increase the ERP or change site.

 

[Carmine5]

We finally decided to diplex. Will get a CP mod for a lower antenna height which, according to the FCC, can be expedited in two weeks. Can get a combiner from Bext at the correct channels by mid-March. Will be using a PTEK G3000 TX which can be delivered in a week. We figure a budget of about 25K to get the station on air. I'm sure we can file a 302 before the April 16 deadline. But we all know about the best laid plans...

 

[bossbill]

pCube helped us with a combiner. 3kw and 10kw into a specially-built antenna.

 

[alleo]

I'm considering building out an FM CP that has come up for sale. In preparing a list of equipment, engineering and specs for the build I've been getting conflicting advice on the the type of coax to use for the antenna.

I was thinking of using Andrew Helax AVA5-50 7/8 virtual air foam dielectric cable with their Positive Stop connectors. They say this combination will effectively seal out moisture. But I'm hearing from an engineer that I should, instead, get Andrew Helax standard air dielectric cable and fill it with CO2.

So which is better for keeping out moisture, gas or no gas?

air pump will do just fine. There are cheep and will keep pos air rate , but its the power level if it. If below the rated level it should do fine with out the pump.