More STL power needed

Gotta watch those Fresnel zones!
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Shane
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Re: More STL power needed

Post by Shane » Thu Jul 07, 2016 12:51 pm

there is an issue and we really only need an additional 2-3dB so I do think a few more watts might work.
You do realize 3dB requires you to DOUBLE your output power which would be 34 watts into the sending antenna. That's quite a bit more than a couple of watts.

I like the idea of an extra antenna lower down but connected thru a remotely controllable relay rather than a "T". You could then switch it in on those 1% days. Put it on a push up mast at the site and you may not even need a tower crew if the tropo is bending the path that much lower.

My experiences with tropospheric bending are that the bent path actually delivers a stronger signal than the normal path so a smaller receive antenna could be used on the lower position which might actually make the reception more reliable during the event and not so dependent on knowing the angle of the bending which is probably not very predictable anyway.

Also, if tropo causes another co-channel STL signal to find its way into the main receive antenna, thus causing interference with your own signal, the lower antenna has less of a chance of picking up the interference.

Somebody just has to be near the remote control to make the switch when the trouble starts and when it ends. If you have a dialup remote control you can do that from anywhere. I'm thinking that's not what you have since you say the telephone service at the site is poor.

No guarantee any of that would actually work. Just me talkin'. But if it can be done cheap it might be worth taking a chance on.
Mike Shane, CBRE
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ChuckG
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Re: More STL power needed

Post by ChuckG » Thu Jul 07, 2016 11:04 pm

la radio guy wrote: 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?
High power stuff isn't too common in the 950 Mhz range. L-com makes a 25W amplifier, $775 new. Crescend makes them up to 140W, but the price is absurd. OTOH I just bought a used Mark dish for $100, I'd start by trying the cheaper solution first.
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Chuck Gennaro
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KPJL FM
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Re: More STL power needed

Post by KPJL FM » Fri Jul 08, 2016 7:42 am

I didn't see where you did a Fresnel path study to determine heights that'll work (on both ends). I'd start with that, for your current installation, then try a few for different positions (heights). For the distance you're trying to get, having a middle 'hop' may be all that'll work reliably. Cost vs. reliability are proportional.
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la radio guy
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Re: More STL power needed

Post by la radio guy » Fri Jul 08, 2016 9:49 am

ChuckG wrote:
la radio guy wrote: 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?
High power stuff isn't too common in the 950 Mhz range. L-com makes a 25W amplifier, $775 new. Crescend makes them up to 140W, but the price is absurd. OTOH I just bought a used Mark dish for $100, I'd start by trying the cheaper solution first.
The L-Com that I see online works in the 902 - 928 MHz range. Does anyone have experience with TPL's amp? They have a 3w in and 40w out.

I did a Fresnel path study when we built this thing out and everything should work and does 99.9% of the time. I'd rather try more power at the send site. I understand about having the license modified and all that. My plan would be to wait until I have a day when the signal is poor and hook up the amp. If it improves the signal, then disconnect it and file to make it legal. If it doesn't, all I'm out is the price of an amp or if it is off the shelf I can just return it. If I add the additional dish at the receive end and it doesn't work I'm out several thousand dollars.

taylorengineer
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Re: More STL power needed

Post by taylorengineer » Tue Jul 12, 2016 1:25 pm

One consideration before getting crazy with transmit power - be careful not to overload the front end of your receiver. Moseley systems will actually be damaged by 2000 uv signals over time. They will tell you to pad the RF.
I agree with Deep Thought. You're missing it during tropo by 10-20 db and it would take one heck of a power increase to make that up. Careful selection of antennae and diversity antennae are the most common solution to tropo induced fading.

level42
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Re: More STL power needed

Post by level42 » Tue Jul 12, 2016 4:38 pm

I have one of these Bext 40 watt STL amps on a station near the gulf coast with a 28 mile STL hop, it helped us overcome the "gulf fades"...haven't had any issues since installing it. STL dish on the TX side is a 6' Mark at 120 feet, on the RX side we have a 6' Mark at 800 feet. No preamp.

http://www.bext.com/2014/02/lka-series-stl-amplifiers/

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