Cable Amplifier for multiple Scanners… for fun

[iceman977th]

Work has announced to remove all cable TV amplifiers as we come across them in preparation for conversion to high-split systems.. soo, there will be a large surplus of unity gain amplifiers soon.

So, just out of blind curiosity, has anyone ever tried using a unity gain cable amplifier to feed signal to multiple scanners before? I know that they are designed for 75 ohm and not 50 ohm like most radios/scanners, and I know it’s not the “proper” way.. but I’m curious how well it would work instead of doing multiple passive tees and short of spending proper money for a proper amplifier.

You know.. for science.

Mike

 

[MTS2000des]

Being that these are broadband by nature, you'll most likely do more harm than damage amplifying hash and trash.

 

[gary123]

I agree with MTS2000des. The concept is good though and this is how multiple receivers are coupled together at a site. Specifically the Rx antenna is connected to a band specific amp and the output of the amp goes to a 50 ohm splitter with as many taps as needed for the receivers. Unused taps are terminated with a 50 ohm load.

Having said all this. If the amps are free or near to it and are band adjustable/selectable you could experiment. The 75 ohm miss match is not going to be a huge difference for RX. keep a c.lose eye on the output levels CATV equipment (TV sets and converters etc) is not as sensitive as a scanner any you could easily pump in a too much signal and damage the scanners.

 

[hp8920]

Depending on how much free junk you can drag home, you could run everything at 75 ohm. Get a TV antenna, leftover hardline and you're set.

This actually isn't a bad way to use free reel end cable. You want the long run to be matched, and you can use the amp as a buffer with short cable sections to the scanners.

 

[Ubbe]

has anyone ever tried using a unity gain cable amplifier to feed signal to multiple scanners before?

Unity gain? What's the purpose of having 0dB gain. If it has a splitter with multiple outputs then it can be used in the same way as a Stridsberg multicoupler feeding several receivers without any loss. The antenna will work as a frequency band filter and most amplifiers can handle a decent amount of out of band signals. The best solution are to have a 6dB-15dB amplifier at the antenna and then have a passive splitter at the receivers and add some additional attenuating to get unity gain from the antenna to a receiver or some extra 6dB signal if the amplifier are a low noise type. Those unity gain drop amplifiers usually are designed to distribute an already amplified signal and then have a very high noise figure.

Do you have the model name and number of the amplifiers?

/Ubbe

 

[merlin]

I use a line drop amp with my setup. Good from 50 Mhz to 1 Ghz and 15 Db gain.
The noise figure is good, but out of the amp, the signal is just too hot for my bearcat.
Even 4 way splitting, I need a 10 Db pad or it overloads the bearcat, and that is with the attenuator on.
Another annotation with preamps is you amplify noise along with signal.
The 75 ohm impedance is no issue with scanners.

https://www.amazon.com/dp/B001EKCGT8/?tag=topcheckprodu-20

 

[merlin]

You may need an FM trap in front of the amp.

 

[Ubbe]

I use a line drop amp with my setup. Good from 50 Mhz to 1 Ghz and 15 Db gain.
The noise figure is good, but out of the amp, the signal is just too hot for my bearcat.
Even 4 way splitting, I need a 10 Db pad or it overloads the bearcat, and that is with the attenuator on.

Your amp has 8dB gain out on each of its four outputs. It has a 3dB noise figure. It seems to be able to handle input signals up to -40dBm. A passive 1-4 splitter has a 7dB attenuation on each output. If you have to use a 10dB attenuation pad and then add the scanners attenuation on top of that then a passive $5 splitter should work and won't add 3dB noise to the signal.

But you seem to have very strong signals in your area so probably no need to do weak signal monitoring, where hunting for the lowest noise figure becomes important, but you could get into trouble if your antenna signals are above -40dBm. The crossmodulation level are 80dB below the carrier so if all signals combined from the antenna adds to be at a -40dBm level then the crossmodulation products starts to be received by the scanner. That's probably pretty bad for an antenna amplifier. Second order distorsion are 60dB below the carrier. If you enable the scanners own 20dB attenuation then you can receive signals up to -20dBm as crossmodulation products in the amplifier will be down at the squelch level -120dBm. The amplifier has no IP3 specifications.

Those cable drop amplifiers are designed to always operate with medium strong signals and can't handle too high signal levels.
You probably have no scanner issues but the overload happens in the amplifier and your attenuation sets the crossmodulation products below the level of the scanners sensitivity where they will not be received. Try a $5 CATV splitter as a replacement and see what results you get.

https://www.amazon.com/CommScope-SV-4G-HomeConnect-Coaxial-Splitter/dp/B0965ZLFDL

/Ubbe