Cross Talk After Connecting Splitter

[ksangree]

I have a strange problem. We are a PA state humane law enforcement agency. We have two Uniden scanners (a BCD536HP and a BCD436HP) that we use to monitor local police: one for the city of Chester, PA, and one for all other Delaware County PA police departments. The feeds are then pumped into two TeamSpeak clients running on separate computers via a cable plugged into theheadphone jack on the scanners to the line-in port on the computers. The TeamSpeak clients are monitored by our LEOs in the field.

Based on a recommendation in the RR forum, I purchased a PCT-MA2-4P drop amplifier to split the signal from our discone antenna. Here is the problem: When I go to connect the second coax going from the splitter to the scanner, I can hear crackling and humming in the PC speakers of the first scanner, similar to if you touch the connector of the computer's line-in cable. Once the coax is fully connected, the output from the second scanner can be heard through the speakers of the computer connected to the first scanner. Weird...

Any suggestions on what may be causing this and how to remedy it?

Link to splitter: RF amplifier passive return CATV amp PCTMA24P | PCT Store

 

[buddrousa]

My first thought is that is a 2 way amp and it amplifies noise in both directions.
My second thought is the isolation between ports.
My third thought is this was designed for TV use.
This is what all the power users here use Multicouplers.

 

[Kb2Jpd]

I have a strange problem. We are a PA state humane law enforcement agency. We have two Uniden scanners (a BCD536HP and a BCD436HP) that we use to monitor local police: one for the city of Chester, PA, and one for all other Delaware County PA police departments. The feeds are then pumped into two TeamSpeak clients running on separate computers via a cable plugged into theheadphone jack on the scanners to the line-in port on the computers. The TeamSpeak clients are monitored by our LEOs in the field.



Based on a recommendation in the RR forum, I purchased a PCT-MA2-4P drop amplifier to split the signal from our discone antenna. Here is the problem: When I go to connect the second coax going from the splitter to the scanner, I can hear crackling and humming in the PC speakers of the first scanner, similar to if you touch the connector of the computer's line-in cable. Once the coax is fully connected, the output from the second scanner can be heard through the speakers of the computer connected to the first scanner. Weird...



Any suggestions on what may be causing this and how to remedy it?



Link to splitter: RF amplifier passive return CATV amp PCTMA24P | PCT Store

You have a ground loop. If the amp is powered, flip the power plug and turn it back on. See if you still have problems.


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[jim202]

I would make sure that your scanner is not connected to the bottom left port on the amplifier to begin with. That port is a DC power connection and you don't want to have a scanner connected to it.

The other issue is this amp gives an 8 db gain out on the 3 ports. That could possibly cause an overload condition on a strong signal. You might have to add a padd to drop that gain down.

The cross talk is probably the IF of both scanners talking to each other. This could be due to a number of reasons. Poorly shielded coax, poorly made jumper cables where the shield is not connected, not enough isolation between the line amp ports or the scanners are just radiating way too much IF signal. It would take the use of a spectrum analyzer to sniff for the IF signal to see if that is the cause.

One last trick to try is a different power source for the scanner. Try a DC power supply on one of the scanners and not use a wall wart. If that works, try putting both scanners on the same DC power supply. You will need to make up power cables to feed both scanners with the correct plugs. If your like me, I never throw away a wall wart. Just toss them into a drawer. So I always have a source of cable with plugs already on them. But use an Ohm meter to make sure you wire the cables up correctly. Normally the center pin is the + or plus connection and the shell is the ground or negative connection. I generally put a piece of red tape on the plus wire at the power supply end to identify it. Check the scanners to make sure this is the way they are wired. Normally the scanner company puts a label near the DC power connector to indicate the plus connection.

Good luck trying to locate the source of your problem. But do let the group on here know what you find.

 

[prcguy]

I agree its a ground loop between computers causing the hum and crackling. This is probably caused by the antenna being grounded to something at a different potential as the computers and when you connect the audio cable to the computer, ground currents flow from the antenna mast through the coax to the scanner to the audio cables to the computer. More than likely the scanner and TV drop amp run from ungrounded wall warts, leaving the computer as the far end of the ground chain.

These currents are flowing as the two different ground potentials are trying to equalize and the AC current flowing on the audio cables induces AC hum into the computer sound cards. One way to eliminate the problem is to use a 1:1 audio transformer at each computer sound card input. You can also get a ground loop eliminator with F connectors for the antenna side.
prcguy

You have a ground loop. If the amp is powered, flip the power plug and turn it back on. See if you still have problems.


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[ksangree]

Awesome! Thanks to all for taking the time to reply. I will try your suggestions and let you all know how I make out.