Multiple receivers attached to 1 antenna - Question

[Jphila20]

Running RG6 for a scanner and SDR. I know not the best. Using a 75ohm splitter, Channel Plus 5MHz-1000MHz, between a TRX2 and SDR's. When I connect the scanner and SDR the signal on the SDR drops by half or more. 100% to less than 50 to zero. Checked cables with a meter and no shorts.
Should I read 50 ohms through the splitter? I'm getting .1 or zero.

Thoughts?

 

[chief21]

By design, these inexpensive 2-port splitters will drop the signal by 3 dB (or half) to each port. A true multi-coupler will compensate for the signal drop. There are other options to explore...

Splitters, Filters and Multicouplers

For discussion of all inline devices used to split, combine or amplify a receive signal. This forum is not for any bi-directional (transmit) device. Use the Amateur or Commercial Radio forums for those.

forums.radioreference.com

 

[mmckenna]

Running RG6 for a scanner and SDR. I know not the best. Using a 75ohm splitter, Channel Plus 5MHz-1000MHz, between a TRX2 and SDR's. When I connect the scanner and SDR the signal on the SDR drops by half or more. 100% to less than 50 to zero. Checked cables with a meter and no shorts.

Like the Chief said, you are taking a signal and splitting it to two different outputs. Each output is going to get a bit less than half the received signal strength. If you look closely at the splitter ports, you'll often see "3.5dB" marked on them. That's the amount of loss involved, or just a bit over half.

You probably want to add a receive amplifier between the antenna and the splitter to make up for the losses.

Should I read 50 ohms through the splitter? I'm getting .1 or zero.

No. Impedance and DC resistance are two different things.

 

[737mech]

Using a regular splitter you see right on it most of the time a -3.5db near every output. As chief21 said half the signal. The multicouplers are the way to go if you can afford them. They are powered with an amp to boost the outputs and make up for that split loss. I personally use the 8 output tv drop amps from Electroline. They are functionally multicouplers and less expensive. Some say not as good as a stridsberg and I would agree it's just my choice to use the cheaper EDA's.

 

[popnokick]

Get an inexpensive one that is a powered splitter / amp / equalizer with multiple outputs.... like this -

Amazon.com

 

[Ubbe]

Using a 75ohm splitter, Channel Plus 5MHz-1000MHz, between a TRX2 and SDR's. When I connect the scanner and SDR the signal on the SDR drops by half or more.

You got several SDR's and one TRX-2 and when you connect one SDR to the splitter the signal level are 100% but when you connect the other SDR and the TRX-2 the signal drops at the first SDR?

When you have the outputs open and not connected to a load like a receiver, then a splitter usually will show a higher signal on that single receiver that are connected. You now use a 3 or 4 port splitter that could be a 6-8dB loss of signal.

That 0 ohm thru the splitter comes from the power pass function, a choke are connected from input to output to enable an amplifier at the antenna to be powered from the coax. Your SDR's probably have an option to output 5v out their antenna port. Check that it isn't enabled as the your antenna could be a DC grounded one that will shortcircuit the SDR.

As you probably already have a 5v source in one of the SDR's that can power the coax you can simply get a low noise amp that are power by 5v from the coax and place up at the antenna. The amp will probably have a 20dB gain that are too much and you have to get a 10dB attenuator or preferable a variable 20dB attenuator to set the perfect level for your receivers.

/Ubbe

 

[bearcatrp]

Get this to fix your issue. 2 ports left for future radios.

Multicouplers

 

[wtp]

one fix...
if you don't need the splitter for the scanner, don't use it.
i helped one guy because he wanted to use a splitter for 3 radios.
2 were surrounding counties and 1 was his local.
i told him the same thing and he could just use the back of the set for the local stuff.
problem fixed.

 

[merlin]

Most bargain basement SDRs don't have much of a front end like scanners do. As is, they all could use some form of preselector.
You run through a spitter, you lose about half of your badly needed gain.
3 Db is about insignificant with multiple scanners.
With my setup, I have a discone on the roof two stories. 65' of LMR 600 into a drop amp into a 3 way splitter. An RG6 line to the TV, A short run of RG 400 to an SDR, and a port for general VHF/UHF equipment. This works OK in spite of any impedance mismatch. The SDR works far better with a preselector and bandpass filtering.
If I plug my bearcat into that open port, the signals are just too hot for the scanner. With the amp bypassed, I still need attenuaton with local signals and get usable 800 Mhz signals from a site 60 miles away. I still need bandpass filtering for being next door to a major repeater and cell site.
737mech offers one solution for you, but don't be surprised your TRX2 needs some attenuation.
Another approach is investing in a better SDR like RSP1 or better.
I could swap out my LMR 600 with a good RG 6 and make literally no difference.
As mmckenna noted, this is RF impedance, not associated with DC resistance.
Cheers.

 

[PD47JD]

Most bargain basement SDRs don't have much of a front end like scanners do. As is, they all could use some form of preselector.
You run through a spitter, you lose about half of your badly needed gain.
3 Db is about insignificant with multiple scanners.
With my setup, I have a discone on the roof two stories. 65' of LMR 600 into a drop amp into a 3 way splitter. An RG6 line to the TV, A short run of RG 400 to an SDR, and a port for general VHF/UHF equipment. This works OK in spite of any impedance mismatch. The SDR works far better with a preselector and bandpass filtering.
If I plug my bearcat into that open port, the signals are just too hot for the scanner. With the amp bypassed, I still need attenuaton with local signals and get usable 800 Mhz signals from a site 60 miles away. I still need bandpass filtering for being next door to a major repeater and cell site.
737mech offers one solution for you, but don't be surprised your TRX2 needs some attenuation.
Another approach is investing in a better SDR like RSP1 or better.
I could swap out my LMR 600 with a good RG 6 and make literally no difference.
Cheers.

Ouch!

 

[dlwtrunked]

Get an inexpensive one that is a powered splitter / amp / equalizer with multiple outputs.... like this -

Amazon.com

Not really a good choice. The goal is to get a better signal-to-noise level. That one does not even state a noise figure nor is the gain high enough to make use of a better noise figure in a pre-amp. In addition, no P1dB = 17 dBm or 3OIP. Falls into not one to buy. As other posted, something like the Stridsberg are the way to go unless you build one yourself buying a good pre-amp from Mini-circuits or elsewhere and out it ahead of a passive splitter. Other things: antenna height is most important and strong signals will require filters (as a minimum, unless you are listening to the FM broadcast band, you want to block tht) and experimenting.

You did not say what SDR...some cheap ones are hard to help. I would only myself use an Airspy or RSP. You cannot get miracles form cheap.

 

[737mech]

I think when considering a tv drop amp just do the math, I have a EDA 8 port with +4db per port. The above posted tv drop amp is +7.5 DB could very well be too hot for your scanner. Depends on what is in your air. Try to keep the math even keel. Starts at 7db/ split is two at 3.5db/ split to 8 port amp 7db becomes .875 per port. Then add the +4db from EDA amps you have 4.875db slightly lower than the original 7 db but not higher to over boost your scanner. The four port is different. 7 db to start split four ways is 1.75 per port then add +7.5db from the amp = 9.25db that could be a problem like a loud crowded room for your scanner.