How good is your signal past the 60db contour

[Groove1670]

A survey: How good is your signal past the 60db. Do you have towns that still hear and benefit from your signal at that range.

 

[Chuck]

A survey: How good is your signal past the 60db. Do you have towns that still hear and benefit from your signal at that range.

Absolutely.

 

[MisterGort]

Central California - Yes. Class A - maybe close to the 57 or 54 dBu contour.

 

[VoiceOfReason]

I usually run Longley's down to 54 dBu, and sometimes 45 dBu to get fringe commuter/car listening.

IMHO, this is one of IBOC's issues - you can get useful analog listenership outside the 60, but IBOC falls apart faster than that, even with power increases.

 

[Groove1670]

Thanks for the replies. I have a Class A I am building, but the 60db falls about 8 miles short of a fairly populated town. The decision is to run full ERP or to go with less power and say a 4 bay antenna? Would would be the best method the get the most coverage? No IBOC planned.

 

[Nostalgia]

Thats 8 looooong miles for your class A! The question in every readers mind is: What does your CP say? I mean, your 60db contour fell 8 miles short when you planned and filed for this license however long ago, why is this question coming up now? To change it as this point would be legally cumbersome and expensive, if it can be done at all depending on your particular circumstances.

All other posters are absolutely correct. Biggest hurdle is the terrain between you and the town you want to penetrate, and if this is a big city with skyscrapers etc, or a small town your now weakened signal can tickle some antennae!

 

[Groove1670]

No skyscrapers. Some bumpy terrain (but pretty flat). No changes in CP. Just looking to maximize signal with the cards we were dealt (no chance of upgrade). Power VS gain. Just looking for real world situations. Not expecting a miracle.

 

[rfry]

I have a Class A I am building, but the 60db falls about 8 miles short of a fairly populated town. The decision is to run full ERP or to go with less power and say a 4 bay antenna? Would would be the best method the get the most coverage?

The calculated distance to the F(50,50), 60 dBµV/m (1 mV/m) coverage radius for a given class of FM station will be the same in all cases, regardless the height of the radiation center of the transmit antenna above average terrain, the number of bays, and the transmitter power needed to produce the authorized ERP.

However using the maximum ERP permitted for the class of station could improve "building penetration" in the primary market(s) closer to the transmit site.

There may be coverage differences in some directions due to the way the antenna is installed on whatever structure is supporting it. In every case it will be useful to purchase an antenna pattern study from the antenna manufacturer for guidance about how best to achieve coverage expectations for the station.

RF

 

[Groove1670]

There may be coverage differences in some directions due to the way the antenna is installed on whatever structure is supporting it. In every case it will be useful to purchase an antenna pattern study from the antenna manufacturer for guidance about how best to achieve coverage expectations for the station.

Thanks, That is the kind of suggestion I was looking for.

 

[oldiesstation]

As the late John Mulanney told me,you just never know till you build it.Theory is great but performance is the real deal.I like ERI but might consider the Jampro penetrator antenna.Don't cheap out on the RF chain.Of course co-channel and adjacents play into the equation.Aren't you near the Gulf coast?Now with tropo,that's a whole new game,as you know it can be murder.

 

[Groove1670]

I like ERI but might consider the Jampro penetrator antenna.Don't cheap out on the RF chain.

Going with Jampro (New). Trying to explore best options. No co channel issues (unless an LPFM or translator pops up). I'm away from the coast.

 

[everydayguy]

I don't know what your format will be, but one option might be going mono rather than stereo. I'm not an experienced engineer -- still trying to learn all I can -- but there have been several discussions on this board in the past about mono vs. stereo and the ability to be heard farther out with less interference when running in mono.

 

[Groove1670]

As the late John Mulanney told me,you just never know till you build it.Theory is great but performance is the real deal.

He was right. I have seen some sign on (class A) with a gangbuster signal, and others that get crushed right after the 60db (co channel etc.)

 

[RadeoEngineer]

Mr. Fry is spot on. I have always been amazed that someone would purchase "the final link" to their listeners (the antenna) without knowing exactly how it should be mounted on the structure, which requires modeling. The attitude seems to be "why should I spend another $5k on an antenna that's brand new that I've already spent $15k, $20k, $35K or whatever." The answer is that it's your final link to your audience and you're going to live with it for something like 30 years. You damn well better know where and how to mount it to get the best results, and the only way I find acceptable to do that is full range modeling, and only ERI and Jampro can do that. Everyone else uses some form of computer modeling or reduced field modeling. You get one shot at this and you want it right.

 

[LA_Guy]

I evaluate FM signals two ways; In street and in building. Typical signals in street go MUCH further then those in building. In street coverage is most always limited by interference (unless you are driving within a steel and concrete jungle like a major city's downtown). In building coverage sometimes doesn't make it to the 60 dbu contour.

In Tucson the cluster I worked for had a C3 FM that we ran mono. It was 425 watts ERP atop a 6000+ foot mountain. In my car it got out to within 25 miles of Phoenix, until an adjacent channel station clobbered it. All total you could hear it clearly almost 80 miles away in the car. YET, in my house (stucco) I had a tough time picking it up on my clock radio (unless it was near the window), even though I was well within the 60 dbu contour-and we could hardly pick it up at the studio at all due to all the computer interference (there was a call center located next door).

I hope this illustrates the HUGE difference between these two coverage concepts. By the way, Public safety has been using these types of evaluations for years.

 

[Groove1670]

You get one shot at this and you want it right.

Very true. The antenna study will be done. That is why all options are being looked at.

 

[Kmagrill]

I'm surprised nobody has yet mentioned this: Call ERI and get a lambda section with a matched antenna. There's nothing else like it. We have a class A here that wanted coverage in a town 45 miles away. They got a 5.8dB boost in the desired direction from the ERI combination that made them competative in the target town. I'd also strongly consider a half-wave spaced antenna.

 

[rfry]

We have a class A here that wanted coverage in a town 45 miles away. They got a 5.8dB boost in the desired direction from the ERI combination that made them competative in the target town.

If by some means fair or foul an antenna+tower had 6 dB more gain in some compass direction than the RMS value of its real azimuth pattern, this is the resulting change in the distance to the 60 dBµV/m F(50,50) contour for a full height and an overheight installation:

Licensed for 6 kW omni ERP from 100m HAAT
Omni Pattern (6kW ERP) --> 28.3 km
+6 dB Gain (24 kW ERP) --> 38.8 km

Licensed for 2.75 kW omni ERP from 150m HAAT (derated for height)
Omni Pattern (2.75 kW ERP) --> 28.3 km
+6 dB Gain (11 kW ERP) --> 39 km

The change in the distance to the 60 dBµV/m contour with a 6 dB increase in ERP is far more significant than produced by the additional HAAT.

That 6 dB gain would help at a distance of 45 miles, but most likely the analog signal there would suffer from multipath effects (picket fencing), and building penetration would be relatively poor.

I'd also strongly consider a half-wave spaced antenna.

Worth considering to reduce the r-f fields around the base of the tower, if needed. But 1/2-wave spacing of a typical side-mounted array from Jampro, ERI etc tends to smooth out the pattern in the horizontal plane, making it more difficult to produce much gain over RMS in some direction without using parasitics (ie, to deliberately make the antenna pattern directional).
//

 

[chriscollins]

As the late John Mulanney told me,you just never know till you build it.Theory is great but performance is the real deal.I like ERI but might consider the Jampro penetrator antenna.Don't cheap out on the RF chain.Of course co-channel and adjacents play into the equation.Aren't you near the Gulf coast?Now with tropo,that's a whole new game,as you know it can be murder.

Yep, our company still has a 1000 foot tower standing in a 'great' location to consolidate some signals that had so much multipath in the primary town that it was unusable. On paper, it looks like the best thing in the world though.

To the OP... DEFINITELY pay for the pattern study when you buy the antenna. I would also suggest you keep the bay count down and put some power out of your transmitter if this town is important to you... Class A, I would do no more than 3 Bay. It takes actual power to penetrate buildings in the fringe.

 

[Kmagrill]

Licensed for 6 kW omni ERP from 100m HAAT
Omni Pattern (6kW ERP) --> 28.3 km
+6 dB Gain (24 kW ERP) --> 38.8 km

The change in the distance to the 60 dBµV/m contour with a 6 dB increase in ERP is far more significant than produced by the additional HAAT.

That 6 dB gain would help at a distance of 45 miles, but most likely the analog signal there would suffer from multipath effects (picket fencing), and building penetration would be relatively poor.

I'd also strongly consider a half-wave spaced antenna.

Worth considering to reduce the r-f fields around the base of the tower, if needed. But 1/2-wave spacing of a typical side-mounted array from Jampro, ERI etc tends to smooth out the pattern in the horizontal plane, making it more difficult to produce much gain over RMS in some direction without using parasitics (ie, to deliberately make the antenna pattern directional).
//

The station in question is in Florida. The station antenna is 150 meters tall with 3kW erp. Because the terrain is smoother than the roughness factor applied to the FCC model, signals tend to go farther here. A Longley-Rice analysis is a better model in most cases. Anyway, the point was that using an antenna specifically designed to extend coverage in a specific azimuth is the best way to maximize rim-shot signals. Modelling a standard antenna, like a Jampro, is good but seldom produces anything like a +6dB lobe. Usually 2-3dB is the best that occurs.

My reason for suggesting the 1/2 wave spacing is that they tend to produce a more even field which reduces multipath in the fringe. The reason that ERI uses the lambda sections is that they are parasitic, but they don't count as such in FCC terms.