Multicouplers & Coax

[BoxAlarm187]

For those out there who use multicouplers, I have a question. I'm looking at a Stridsburg active 4-port model, and wondering what coax y'all use to go from the multicoupler to the individual scanners?

Naturally, RG-8 would be easiest to run, but I know there are concerns with loss in this line. Since all of the runs would be less than 24", is this still a concern? I could run some "big stuff" if I have to, but wanted to see what the others do.

As always, thanks! 8)

 

[N_Jay]

For those out there who use multicouplers, I have a question. I'm looking at a Stridsburg active 4-port model, and wondering what coax y'all use to go from the multicoupler to the individual scanners?

Naturally, RG-8 would be easiest to run, but I know there are concerns with loss in this line. Since all of the runs would be less than 24", is this still a concern? I could run some "big stuff" if I have to, but wanted to see what the others do.

As always, thanks! 8)

The loss after the preamp is trypically irrelevent.

 

[BoxAlarm187]

The loss after the preamp is trypically irrelevent.

OK, sounds good. However, this brings up another question. Does the fact that the multicoupler is "active" make it behave like a pre-amp? I was under the impression that the fact that it's active simply reduces loss between each of the ports.

Ack, don't need an amp, just a good way to split my scanners! :lol:

 

[N_Jay]

The loss after the preamp is trypically irrelevent.

OK, sounds good. However, this brings up another question. Does the fact that the multicoupler is "active" make it behave like a pre-amp? I was under the impression that the fact that it's active simply reduces loss between each of the ports.

Ack, don't need an amp, just a good way to split my scanners! :lol:

The fact that it is active means that it has an amplifier in it.

A receivers sensitivity is set principaly by the noise figure of the first amplification stage, Unless there is enough loss after that stage to get back to the noise floor of the next stage (rare and a bad design).

This gets into why an amplifier can amplify the signal and not make it any better.

 

[Voyager]

For those out there who use multicouplers, I have a question. I'm looking at a Stridsburg active 4-port model, and wondering what coax y'all use to go from the multicoupler to the individual scanners?

Naturally, RG-8 would be easiest to run, but I know there are concerns with loss in this line. Since all of the runs would be less than 24", is this still a concern? I could run some "big stuff" if I have to, but wanted to see what the others do.

As always, thanks! 8)

RG-58 would be much easier to run, and since you are only talking about a couple feet, the loss isn't an issue. Thus, anything more is a waste.

If you are using it on 800 MHz, try to stick with BNCs and stay away from UHF connectors. They totally blow at 800 MHz. (another reason RG-58 is better than RG-8 - BNCs for 8 are much harder to find)

Joe M.

 

[Halfpint]

The loss after the preamp is trypically irrelevent.

OK, sounds good. However, this brings up another question. Does the fact that the multicoupler is "active" make it behave like a pre-amp? I was under the impression that the fact that it's active simply reduces loss between each of the ports.

Ack, don't need an amp, just a good way to split my scanners! :lol:

Basically what the `amp' in the Stridsburg multicoupler does is eliminate the losses of the splitter in the coupler. So what you get out at all the out ports is the same as what appears at the in port. I've got an 8-port one and it *definitely* works! In fact I don't even get any cross coupling between may scanners like you can get by just using a `passive' `TV' style coupler. It's great when you have scanners `listening' to VHF LO/Hi, UHF Lo, and Trunked UHF hi all going at the same time. Since installing mine I haven't had a single `lockup' caused by one of the older scanners like I used to.

*If* you are planning on getting any more scanners than just 3 - 4 going any time in the future investing in one of the 8-port couplers now would be the way to go. All you have to do is just slap some 72/75 ohm terminators on the unused ports and remove them as you add radios. (I just picked up some 72/75 ohm `cable' terminators and `adapted' them to the BNCs on mine. As soon as I can get a pair of PRO-2006s I'll just remove a couple and basically `drop' them in and be up and running almost immediately without hassling with adding anything else like I would have to have done previously. {GRIN!}) BTW, I'd actually consider `terminating' any unused ports on even that 4-port one! And... Don't worry... 50/72/75 ohm terminators... for *receive* it isn't going to matter. You just want to `terminate' the `ports' with *something* in that `range'.

 

[runslow]

BoxAlarm187 - Check your pm ........

 

[N7OLQ]

I have an 8 port active multicoupler that is full, so one of the 8 ports feeds a 4 port active multicoupler (which is also full now). All the outputs work great and as was mentioned, the amplification is really just to overcome the losses associated with inserting a splitter and dividing the signal up so many ways. I use BNC-BNC RG58 patch cords (mostly from Radio Shack) and the setup works great.

As a comparison, I plugged in the feedline (BuryFlex) from the antenna directly to one of the scanners, but could not detect any difference between the multicoupler output and the direct feed.

If you have multiple scanners and need/use an outdoor antenna, the Stridsberg Active multicouplers are THE most valuable shack accessory there is.

As a side note, you can also use a PASSIVE multicoupler to connect 2 antennas to one scanner (for example 2 yagis covering different bands). There is less need for that these days since everything is moving to 800MHz, but one possible application is to combine 2 800MHz yagis pointing is different directions. You could then feed that to an active multicoupler and feed all the scanners in your shack with just the right mix of signals.

 

[N_Jay]

I have an 8 port active multicoupler that is full, so one of the 8 ports feeds a 4 port active multicoupler (which is also full now). All the outputs work great and as was mentioned, the amplification is really just to overcome the losses associated with inserting a splitter and dividing the signal up so many ways. I use BNC-BNC RG58 patch cords (mostly from Radio Shack) and the setup works great.

As a comparison, I plugged in the feedline (BuryFlex) from the antenna directly to one of the scanners, but could not detect any difference between the multicoupler output and the direct feed.

Due to the nature of FM you will only detect a difference in margional signals. The fact that you do not detact a difference does not maen one does not exist.

 

[N7OLQ]

Yes, I know. I monitor 1 trunked site that is right on the fringe. Just above the noise level. Even the weather affects how well it comes in. I generally use, not just the scanner audio to judge, but the % decode of Trunker running on the control channel.

 

[N_Jay]

Yes, I know. I monitor 1 trunked site that is right on the fringe. Just above the noise level. Even the weather affects how well it comes in. I generally use, not just the scanner audio to judge, but the % decode of Trunker running on the control channel.

Are you noise limited rather thna signal limited?

It woule be an amazing coincidence to have the amplifier gain exactly equal the splitter loss, and and the amplifier noise figure exactly equal the scanner front end.

Why don't you put the amplified coupler first and feed the 8 way?

The less loss you have before the first stage of amplification the better.

 

[N7OLQ]

It is a little of both. There is a mountain in the way, and some nearby 900MHz pager towers so the amplifier noise is small relative to what is already coming down the line.
Both multicouplers are 'active' with about 4dB gain so it makes no difference. which comes first.

 

[N_Jay]

It is a little of both. There is a mountain in the way, and some nearby 900MHz pager towers so the amplifier noise is small relative to what is already coming down the line.
Both multicouplers are 'active' with about 4dB gain so it makes no difference. which comes first.

Are they the same noise figure?

I would put the lower noise figure first if there is any difference.

 

[N7OLQ]

I just checked the specs and both Stridesberg models are +4dB +/- 1.5dB gain. The 8 Port is 2.5dB Noise figure, and the 4 port is 3.5dB. I had assumed they were the same, but as it turns out I have them hooked up in the right order.