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HELP!

S

spindoctor1

Thanks to everyone with the help on the Optimod phase issue. I'll be calling Bill for the setting issue.
Now I need to be talked to like a 4 year old PLEASE. I have major multipath issues with my broadcast city which is only 8 miles from my tower. Any ideas how to fix this? Turn the antenna toward or away from the area?
Thanks!
 
It depends on your antenna model, the pattern it puts out, and the way it is currently mounted.

I'm guessing this is a class A station, because that's the only way I'd be expecting multipath at 8 miles. (Either that, or there is some kind of hill between your tower and community)

You should really seek the council of a qualified engineer who can analyze your specific situation.
 
How many bays do you have? How much transmitter power vs. ERP? If you've got lots of bays close to town you'll have a ton of nulls that have to be accounted for. Eight miles out is a bit further down the road that normally a guy would see nulls, but it just depends on the variables. Do you have something it is potentially bouncing off of like tall buildings or a hill, etc? Also, what is the placement on the tower and how big of a face of tower is it hanging off of? If you have a big fat TV tower behind your bays and it's not stood off quite a ways it will really affect things. Sometimes that's a good thing if you want it to push out more one way or another by adjusting the distortion the way you want while still filing as an omni. The bad thing is many just put the damn thing up and guess. That's a great way to have a crappy signal where you really need a good signal, etc. What type of antenna do you have? If you have an ERI they have some examples available of previous studies that you can guess, by your tower size, placement, and frequency, how it will likely turn out. If you have an ERI, I'd gather your info and call Bob Groome. A few minutes with that guy and you'll have a pretty good idea of what to do. Good luck!
 
Here in OKC we have a couple broadcast groups that went in together on a panel antenna. It's about the equivilent of a 12 bay that's in the NE part of the city (tower farm) which is about 4 to 5 miles from the center-city. They also have HD capablities. One group has already abandoned running HD because there are plenty of nulls (even though the antenna is SUPPOSED to have null-fill) and the HD in areas was stronger than the analog because it is an interleaved system and doesn't always arive at the same precise spot in equal portions. It was enough that they actually had some of the public calling up and bitching about it so they just killed the digital.
 
It could be 'optimoditis'. Make sure that if you are using an Optimod, that its output goes into the UNBALANCED composite input of the exciter. If you are running it into the balanced input, you will get the symptoms you are describing.
 
I'd make sure everything is tune4d spot - on. Minimum synchronous AM and best 38KHz supression will lessen the problem. They're both often perveiced as 'multipath' though they aren't really. Also, if you have a stereo enhancer of any sort, lose it quickly. They can do Bad Things tto reception.
Just for information, what make/model of transmitter and line and antenna?
 
Think everybody's covered it so far. Put a mod-monitor on it and check the 38khz suppression. I think there are adjustments on the older Optimods for that.

If running a 950MHz composite STL, check for noise or other issues with the STL system.

Some stations in really rugged terrain will stay mono to lessen the multipath effect.
 
One more thing..

One more thing: If you are running a Harris exciter, chances are its only composite input is balanced. In this case you need to ground the shield of the coax coming from the Optimod to the chassis of the exciter.
 
Guys,
Thank you for all the great info. It's is price less. (This should be a Mastercard ad)
This station has been resurrected from basically a pile of crap.
I rebuilt the transmitter from the ground up and installed new transmission line
to the "somewhat" ancient Phelps-Dodge 2 bay. New exciter as well.
The Optimod has been giving me a fit on the pilot side but I THINK with all
the info I have been given here I can get it closer to spot on.
I have been told by a 40 year engineer that this area is notorious for
multipath and I would do well to get a low power signal booster near the
areas that need to be filled in. (Just to let you know this is one of only two cities
iin the US to built inside a meteor crater)
HOWEVER, I can't seem to find a good company
that makes them. Any suggestions?
Thanks in advance.
 
spindoctor1 said:
Guys,
Thank you for all the great info. It's is price less. (This should be a Mastercard ad)
This station has been resurrected from basically a pile of crap.
I rebuilt the transmitter from the ground up and installed new transmission line
to the "somewhat" ancient Phelps-Dodge 2 bay. New exciter as well.
The Optimod has been giving me a fit on the pilot side but I THINK with all
the info I have been given here I can get it closer to spot on.
I have been told by a 40 year engineer that this area is notorious for
multipath and I would do well to get a low power signal booster near the
areas that need to be filled in. (Just to let you know this is one of only two cities
iin the US to built inside a meteor crater)
HOWEVER, I can't seem to find a good company
that makes them. Any suggestions?
Thanks in advance.
Click to expand...

A fill-in translator or booster station may help you. Since you're only 8 miles out, the area you're trying to fill-in should be inside the 60 dBU contour which makes you eligible for either of those. Engineering the translator may be easier as it will be on a different frequency so you don't have to deal with tricky issues of placing the area of self-interference or trying to use synchronization between transmitters. The only issue is that you have to brand with two frequencies and make sure listeners are aware of the translator.

However, you'll have to wait for an FCC "window" to apply for a translator or booster...unless you can find someone with an unbuilt translator application or active translator in the area you are trying to cover and talk them into selling it. So in the mean time you'll want to work on the facility you've got to get it the best it can be.
 
A booster would not require waiting for a window, but a booster would not likely be the cure in this case.
 
8 miles is inside the city grade for a class A (unless there is actually a mountain between the transmitter and the city with the problem). Boosters work best on towards the edges of the protected contour (60 dbu for an A).

We've been running a booster for 20 years on our B-1; both a "conventional" booster (receiver on one side of the hill, long cable buried to the other carrying 10.7 IF signal, then beat back up to operating frequency) and a more "typical" booster (STL feed to a 30 watt exciter). The key to a successful booster is:

A. City in a ditch, well shielded from main transmitter;
B. An interference zone with very little population;
C. A good transmitter site for the booster that will "flood" the urbanized area with signal.

We're on a hill overlooking town, but a low site in town would work as well if you can get audio to it (2 hop STL, for example). There have been various schemes to minimize the interference zone with synchronized carriers, pilots, etc., but I have not been impressed. Propagation changes too rapidly in our area.
 
Tom T,
Can you tell me where you got your booster.
I have check the Audemat site but it is very vague.
Is this affordable or do I need to take out a new
mortgage on the station?
About what am I looking for a unit and extra equipment?

Thanks in advance,
Brian
 
Our original set-up used a Tepco product--http://www.rapidnet.com/~tepco/ I don't know if they still make boosters. This was one of the receiver modules out of their translator line, with its own power supply, and an output of the 10.7 IF, that fed the separate transmitter unit in another box. Believe the power came from the receiver through the center conductor of the coax. We put the receiver on one side of a hill--towards the main station--and buried about 1000' of cable over to the transmitter on the other side of the hill--towards the town.
(1200 ft amsl)
<to station .............................
....... .............
<<<<< ..... .............
[] ... .......... >>>>> to town in valley below
[] ... .......... [] at 600~640' amsl
receiver... (receiver and transmitter 1000 ft apart []
93.9 93.9 transmitter


As you can see by this set-up (if all the dots translate right) the problem is keeping transmit RF out of the receiver. Becomes a limitation on how much power you can put into the booster.

Our present set-up is much simpler. We built the booster in 1988, but abandoned it about ten years later when the long cable died. Then we built a Class A on the same farm above the town. Now we have two STL paths from our main studio, one carrying audio for the Class A, the other, the composite audio for the booster for our other station. All we use for the booster, equipment-wise, is a 30 watt BEXT (RVR) exciter, and a one-bay SWR antenna on 20 feet of 12" tower out behind a barn. The exciter was $1k used, the antenna $500.

Of course you will need STL, antennas, etc., to feed the booster; we got a 606 used for this purpose & our Omnia has two composite outputs--making it easy to feed both STL and main transmitter.

Before embarking on this path I would look at two other options:

1. Ditch the Phelps Dodge two-bay for an ERI antenna. Yes, you can do all kinds of modeling, etc., but I don't think you can get the $$$ from ownership to do that. Just swap out antennas. I'll bet you notice some improvement.

2. If you still want to look at a booster have a consulting engineer run a study. He will be able to give you the idea of how much power you can run on the booster, where the interference zones will be, etc. I've been quoted about 2500 for such a study
 
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