More STL power needed

Gotta watch those Fresnel zones!
la radio guy
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More STL power needed

Post by la radio guy » Tue Jul 05, 2016 12:53 pm

I need more power Scotty !

I have a Marti STL-20C on 944.500. My hop is about 19.5 miles. The output is 20 watts maximum. With the line loss I'm putting out about 17.5 watts at the send dish.

I'm located near the Gulf Coast where we get these strange temperature inversions and with the extreme high humidity it occasionally raises heck with my STL signal. I’d like to try raising the power output to 25 to 30 watts. Of course, I’d amend our license to be legal. Is there an output amplifier I can use or can the unit be modified to get more power? I've tried an amplifier on the receive end but it only amplifies what is received.

There is no internet access at the receive site and telephone service is not reliable there either so an STL is the best option.

Any suggestions would be greatly appreciated.

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Deep Thought
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Re: More STL power needed

Post by Deep Thought » Tue Jul 05, 2016 3:50 pm

10 or 15 more watts TPO isn't going to make much difference (2-3 dB). What antennas are you using now?
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TPT
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Re: More STL power needed

Post by TPT » Tue Jul 05, 2016 4:43 pm

1. Get a boost amplifier on the receive end. I have a 25 mile path, 6' dish on transmit, 8' dish on receive. No problems
2. As suggested, antenna gain and size more important
3. Another suggestion, depending on the receive location--mount two antennas at different levels and "T" the feeds into the receiver.

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Re: More STL power needed

Post by Deep Thought » Tue Jul 05, 2016 5:09 pm

"I've tried an amplifier on the receive end but it only amplifies what is received."

To me this indicates that the transmit and receive antennas are too small for the path, but we won't know until the OP reports back.
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Dale H. Cook
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Re: More STL power needed

Post by Dale H. Cook » Tue Jul 05, 2016 7:05 pm

TPT wrote:--mount two antennas at different levels and "T" the feeds into the receiver.
Depending upon the confguration that may be problematic. I had a station in northeastern North Carolina with a path largely across salt and brackish water. I used two identical receivers with space diversity antennas and a comparator driven by the signal strength lines that steered the composite input of the exciter to the output of the STL receiver with the highest signal strength.
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la radio guy
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Re: More STL power needed

Post by la radio guy » Wed Jul 06, 2016 8:01 am

I'm using a 6' dish for the send and 8' for the receive.

The path should be fine. I've had it aligned. I'm at 100' asl at the send and almost 600' asl at the receive with no obstructions along the way.

I have tried an amplifier from Advanced Receiver. 99% of the time I have plenty of signal anyway. Without the amplifier it has one of the better STL signals I've ever had. The signal level is usually over 1000 and with the amplifier the signal is 1500 to 2000.

The problem I have is definitely weather related. It seems like something that occurs to coastal stations. The signal level will drop down to 10. I've had this issue before and we used an internet feed as a backup. At this site I don't have internet and phone service has been very unreliable.

If I can get just a couple more watts out of this I should be fine on days that the weather is doing its thing

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Dale H. Cook
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Re: More STL power needed

Post by Dale H. Cook » Wed Jul 06, 2016 8:43 am

la radio guy wrote:The problem I have is definitely weather related. It seems like something that occurs to coastal stations.
It occurs most frequently in areas with high temperatures and high humidities, especially along the southeastern and Gulf coasts in the summer. The conditions cause the STL beam to bend so it is no longer aligned with the receive dish, thus causing fading.

We used space diversity reception so that when the beam bendt downward it hit a lower dish. The spacing depends upon the beamwidth of the system.
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kkiddkkidd
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Re: More STL power needed

Post by kkiddkkidd » Wed Jul 06, 2016 11:04 am

la radio guy wrote:I'm using a 6' dish for the send and 8' for the receive.

The path should be fine. I've had it aligned. I'm at 100' asl at the send and almost 600' asl at the receive with no obstructions along the way.

I have tried an amplifier from Advanced Receiver. 99% of the time I have plenty of signal anyway. Without the amplifier it has one of the better STL signals I've ever had. The signal level is usually over 1000 and with the amplifier the signal is 1500 to 2000.

The problem I have is definitely weather related. It seems like something that occurs to coastal stations. The signal level will drop down to 10. I've had this issue before and we used an internet feed as a backup. At this site I don't have internet and phone service has been very unreliable.

If I can get just a couple more watts out of this I should be fine on days that the weather is doing its thing

I don't know if I have ever saw a STL PA for that high of an input. Crescend Technologies could probably do a custom tune on one of their UHF amps. I think that they make UHF amps up to 150w.

With that said, I wouldn't make any bets on it working 100% even at 150w out if you are getting caught up in a coastal ducting event...

Regards,
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Re: More STL power needed

Post by grich » Wed Jul 06, 2016 12:20 pm

Dale H. Cook wrote:
la radio guy wrote:The problem I have is definitely weather related. It seems like something that occurs to coastal stations.
It occurs most frequently in areas with high temperatures and high humidities, especially along the southeastern and Gulf coasts in the summer. The conditions cause the STL beam to bend so it is no longer aligned with the receive dish, thus causing fading.

We used space diversity reception so that when the beam bendt downward it hit a lower dish. The spacing depends upon the beamwidth of the system.
I think this is what Long Lines did with some of their 4-gig paths back in the day. It's probably the only real solution to ducting-related fades.

It happens in Corn Country, too. Our TV station faded 6 times today during the morning show. Humid and warm, with several leftover boundaries from overnight storms floating around.

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Re: More STL power needed

Post by Dale H. Cook » Wed Jul 06, 2016 1:13 pm

grich wrote:I think this is what Long Lines did with some of their 4-gig paths back in the day.
I know that the local telco (probably Southern Bell) was using it in microwave links along the Outer Banks by the early 1980s when I was there.
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Re: More STL power needed

Post by Deep Thought » Wed Jul 06, 2016 1:45 pm

la radio guy wrote:If I can get just a couple more watts out of this I should be fine on days that the weather is doing its thing
Again, unless you are only 'missing' by about 2-3 dB, a few more watts isn't going to make any difference. As mentioned above your problem is the *path* is changing by more than 10-20 dB due to the ducting conditions. With a receive antenna at 600 feet there is plenty of room below it for the beam to be bent under the antenna. Ironically, the large dish antennas and their very tight beamwidth may be making this worse.
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la radio guy
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Re: More STL power needed

Post by la radio guy » Thu Jul 07, 2016 9:21 am

I've watched it at the receive end on days when there is an issue and we really only need an additional 2-3dB so I do think a few more watts might work. I'd like to try that first. The cost of adding a second dish with a tower crew and 500+ feet of feed line won't be cheap.

Just wondering if anyone knows of a STL transmitter that puts out more than 20 watts or of a small amplifier that will get me to 25 or 30 watts. Also, has anyone ever modified a Marti STL-20C to put out more power?

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Re: More STL power needed

Post by Dale H. Cook » Thu Jul 07, 2016 9:46 am

la radio guy wrote:Just wondering if anyone knows of a STL transmitter that puts out more than 20 watts ...
In order to use one you would likely need to have your STL license modified and would likely need to go through frequency coordination, so those costs might make the costs of diversity reception more attractive.
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Re: More STL power needed

Post by jammerdave » Thu Jul 07, 2016 11:33 am

I think I might look into a receive antenna much lower on the tower to get below any ducting/temp inversion issues first.

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Re: More STL power needed

Post by Dale H. Cook » Thu Jul 07, 2016 12:10 pm

jammerdave wrote:I think I might look into a receive antenna much lower on the tower to get below any ducting/temp inversion issues first.
To optimize such an installation you need to know the beamwidth characteristics of your system. When you decide at what level you want the lower dish to take over you can utilize the beamwidths of the existing system and the new dish to determine the optimum elevation of the new dish.
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