Masthead amplifier (TV) with SDR dongle

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Tom41
Posts: 6
Joined: Sun Dec 30, 2018 8:23 pm

Masthead amplifier (TV) with SDR dongle

Post by Tom41 » Sat Jan 05, 2019 10:27 am

I've been thinking about trying my TV antenna with my SDR dongle, to see if it picks up any more signals than the simple aerial that came with it. Problem is, my antenna has a masthead amplifier on it, and there's a power unit that sends power up the coaxial cable to power it. TVs don't seem to care about this voltage on the antenna, but I'm concerned that the SDR might. Is it safe to connect a powered TV aerial cable to an SDR, or will that blow the dongle?

I did, however, check with a multimeter and I can't see any DC or AC voltages across the two pins of the antenna cable.

ScanCaster
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Joined: Sat Jul 22, 2017 7:27 am
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Re: Masthead amplifier (TV) with SDR dongle

Post by ScanCaster » Sun Jan 06, 2019 9:18 pm

Tom41 wrote:
Sat Jan 05, 2019 10:27 am
I've been thinking about trying my TV antenna with my SDR dongle, to see if it picks up any more signals than the simple aerial that came with it. Problem is, my antenna has a masthead amplifier on it, and there's a power unit that sends power up the coaxial cable to power it. TVs don't seem to care about this voltage on the antenna, but I'm concerned that the SDR might. Is it safe to connect a powered TV aerial cable to an SDR, or will that blow the dongle?

I did, however, check with a multimeter and I can't see any DC or AC voltages across the two pins of the antenna cable.
These types of antennas normally have a device on the inside, a power inserter, which "inserts" the power needed for the amp to the coax on the ANTENNA SIDE, and has a block on the TV SIDE port to block the DC.

Some TV's and devices might tolerate this voltage for a while but most it will fry the front ends!

DO NOT EVER CONNECT such devices WITHOUT the PROPER POWER INSERTER!!

I use several setups to provide a distributed antenna setup for my stuff I use a proper power inserter AND A DC BLOCK on the out put! Double sure no DC comes out to the devices....

As for using the TV antenna... What are you expecting to get????

First TV is horizontal polarization... see the rods of the antenna they go horizontal... LMR is VERTICAL which means you are 90 degrees off. There is a huge loss in polarization differences...20-30db is common... this is why its used in things like satellite..

TV uses this as there are propagation properties that are more desirable for horizontal v. vertical... Vertical has better ease of use for the applications...

For really strong signals it may not matter, but for weaker ones you could actually null them out.

So what are you after ??? Getting a proper antenna and mounting it up by the TV antenna is the best bet... The ones included in with the standard dongles are designed for signals putting out 1KW to 1000KW of signal thats a far distance from the 500-600W or most likely LESS of a typical LMR setup...

My repeaters on P25 have a 300W EIRP which is after the gain of the antenna... Mobiles only put out 35W to the systems....

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