Stacking Multi-couplers?

Anyone try this before?

I have one scanner antenna that really outperforms everything else I have on all bands.

I was thinking of trying connecting it to a 4-port Stridsberg multi-coupler, then connecting a pair of 8-port Stridsbergs to that along with a 4-port and an R8500 to the open port on the first 4-port.

I use a whole batch of scanners, 6 for Fire toneouts, 6 for Pro96Com and several others for general listening, railroads and aircraft.

I don't know what they charge but I know at one time they offered a custom 16 port multicoupler.
I run a 4 port off one port of an 8 port multicoupler and am happy with the results.

chris

Rich, I don't see any reason why it wouldn't work. Just keep in mind that you will multiply the insertion loss (or gain, if the couplers have built-in amplifiers) for each level of your multi-coupler cascade.

Every time you split a signal, you loose 3dB for two ways, 6dB for four splits etc. Stridsburg overcome this loss with a small amount of amplification to overcome the splitting loss in some of their models, but the down side is you then add a little bit of noise via the amp. It will work, but not quite as well as if each receiver had one dedicated antenna... but from the number of receivers you have, sounds like it'll be a whole lot neater & cheaper.

W9RXR said:

Rich, I don't see any reason why it wouldn't work. Just keep in mind that you will multiply the insertion loss (or gain, if the couplers have built-in amplifiers) for each level of your multi-coupler cascade.

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One of the real time big blunders is stacking active amp / multicouplers in series. You will bring up the noise floor and probably cause all sorts of intermod problems in your scanners and receivers. If you have any strong signals like any paging transmitters near you, your just asking for problems.

If your talking about using an active amp and it has multiple outputs or power splitters on the output, you can possibly get away with it. Bear in mind the losses that each of the power splitters will introduce. A good amplified multicoupler will also have band pass filters so that your not allowing the DC to white lightning signals to try to pass through the amp and cause it to be swamped out on strong signals your not looking for.

Cheap and working well don't live together in this kind of device. The tower top amps used in trunking systems and some public safety applications have some expensive filters to only allow the desired signals to pass. All the rest are filtered out to prevent problems.

It can be done, but there's a right way and a dozen wrong ways to do it. Here's how to do it right:

A low noise amplifier (with prefiltering in front of it) drives a splitter. The splitter in turn drives several more low noise amplifiers, each of which drives it's own splitter. Depending on the characteristics of the low noise amplifiers, external attenuators are applied to the amplifier outputs to avoid excessive gain and overdriving any following gain stages.

The salient point here is that one preamp sets the noise figure for the entire system. Each preamp provides enough gain to overcome the loss of any following splitters, and any excess gain is attenuated so that overall, from antenna port to each receive port, the total gain is only a few db. Very low noise amplifiers are required, to avoid destroying the good noise figure set by the first gain stage.

Just cascading Stridesburg multicouplers might appear to work on strong signals, but would probably destroy weak signal reception. Stridesburg multicouplers have noise figures in the 2.5 db to 3.5 db range, which is not good enough to cascade without degridation.

Personally I would NOT take the output of one multicoupler and feed it into another multicoupler/amplifier. Your best solution is to acquire a multicoupler that has enough outputs.

Your second solution is to feed your antenna into a passive splitter (think cheapo cable TV splitter) and feed each signal from that splitter into multicouplers. Yeah you get ~3.5dB of loss from that first split, but it will produce less issues.

Well, for grins and giggles mostly I tried something here.

I took my best scanner antenna and connected it to a BCD996XT and then an Icom R8500 and noted signal strengths on a couple channels that transmit all the time (couple of NWS, ATIS, 700 and 800 MHz. TRS control channels, UHF AVL data and a local 49 MHz. baby monitor) on various bands.

I then connected that same antenna to a 4-port Stridsberg and noted the signal strength on the same channels. The results were slightly better with the multicoupler, as it has a small amount of amplification. No hint of interference could be noted.

I then connected my two 8-port Stridberg multicouplers to the outputs of the 4-port. Again I connected the radios to these two multicouplers and the results were very similar to the first test. Some channels were ever so slightly stronger after the second multicoupler was added to the mix but most of them I could not see any difference from the signal strength meters of the two radios. Again, no interference was noted.

Third, I added my trusty Wingard DA-1009 TV amplifier before the 4-port. This is the absolute best RF amplifier I have ever used, about the size of a construction brick and about as strong. I have had it for 10 years or more and it works great from lowband thru 900. After insertion all freqs jumped in strength and I even had an issue with one of my weather channels getting hetrodyne from a co-channel station in the next state.

All in all I think it works fine for me. I am in a suburban location and do not have too much problem with signal overload except for a taxi data transmitter a few miles away.

I think if I ever find a good passive 32-port multicoupler or splitter I will do very well using the Wingard ahead of it.

N9JIG said:

Well, for grins and giggles mostly I tried something here...

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Unfortunately, your test is flawed. There are several other measures of how well it's actually working, besides signal strength.

One of the most important ones is noise figure. Adding a preamp (or preamplified multicoupler) in front of a receiver that has a better NF than the preamp does, will show the symptom of increasing the amplitude of strong signals, and masking weak ones under a layer of noise.

The noise between stages is cumulative, so in order to make a real weak signal improvement, one has to add a preamp with a low enough noise figure and just enough gain to overcome the NF of the following stages.

The other issue to watch for is compression of the various gain stages you have cascaded together. Even just the noise output of some line amplifiers can be enough to drive a following stage into compression. that would make it much more susceptible to intermod.

If the NF of your receivers is mediocre enough, it's quite possible to see improvement by adding slightly less mediocre preamps, which is what I think is actually happening when people report drop amps as having made substantial improvement.

zz0468 said:

Unfortunately, your test is flawed. There are several other measures of how well it's actually working, besides signal strength.

One of the most important ones is noise figure. Adding a preamp (or preamplified multicoupler) in front of a receiver that has a better NF than the preamp does, will show the symptom of increasing the amplitude of strong signals, and masking weak ones under a layer of noise.

The noise between stages is cumulative, so in order to make a real weak signal improvement, one has to add a preamp with a low enough noise figure and just enough gain to overcome the NF of the following stages.

The other issue to watch for is compression of the various gain stages you have cascaded together. Even just the noise output of some line amplifiers can be enough to drive a following stage into compression. that would make it much more susceptible to intermod.

If the NF of your receivers is mediocre enough, it's quite possible to see improvement by adding slightly less mediocre preamps, which is what I think is actually happening when people report drop amps as having made substantial improvement.

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Absent a service monitor I can't really address the noise figure or gain compression. What I can say is anecdotal at best.

It works well for me, I haven't noticed any interference nor have I had to increase the squelch settings.

This seems to work well for a home based hobby scanner station, I certainly would never suggest it for a mission critical application.

Multiple amplifiers before receiver

N9JIG said:

Well, for grins and giggles mostly I tried something here. ... and then ... noted signal strengths on a couple channels that transmit all the time ... I then connected that same antenna to a 4-port Stridsberg and noted the signal strength on the same channels. ...

Third, I added my trusty Wingard DA-1009 TV amplifier before the 4-port. ... I am in a suburban location and do not have too much problem with signal overload except for a taxi data transmitter a few miles away.

I think if I ever find a good passive 32-port multicoupler or splitter I will do very well using the Wingard ahead of it.

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All I read here is SIGNAL STRENGTH. Of all the issues you will encounter, signal strength is not on the (top of the) list. You're adding amplification ahead of more amplification and then a receiver, of course signal strength is going to be "ok".

zz0468 mentions noise floor, how about intermod? Why even ask for our opinions if you're going to do this anyway, and then base your decision solely on signal strength? It is NOT a good idea to cascade amplifiers, especially like this.

gmclam said:

All I read here is SIGNAL STRENGTH. Of all the issues you will encounter, signal strength is not on the (top of the) list. You're adding amplification ahead of more amplification and then a receiver, of course signal strength is going to be "ok".

zz0468 mentions noise floor, how about intermod? Why even ask for our opinions if you're going to do this anyway, and then base your decision solely on signal strength? It is NOT a good idea to cascade amplifiers, especially like this.

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All I can say is so far so good. I haven't had any instances of intermod or other interference products.

There are two things I can measure with what I have: signal strength as measured and displayed by the radios at hand and how it sounds and works. If I had a service monitor, scope or other tools I might find that the actual results are not as cherry as I thought.

The desired end was satisfactory results to allow one antenna to serve a boatload of scanners. The original question was poised to see if there are perils to watch for or better ideas. Obviously the best way would be to have a multicoupler with more ports than the 8 that my largest has, but absent such an animal I wanted to see if I could deal with it with the resources at hand.

What I have found is that I do get satisfactory results, it might not be pretty and if I did some more scientific testing I might find flaws in them that I can't find now, but it works. Your mileage might vary.

For me this is good enough. I wouldn't (and haven't) done this at work, but being that that is a mission critical environment, it isn't right to do so. Of course I have a lot more money available to provide professional equipment and qualified personnel to design, install and maintain it there. At home it has to fit my radio budget and I have to do it myself.

N9JIG said:

Absent a service monitor I can't really address the noise figure or gain compression. What I can say is anecdotal at best.

It works well for me, I haven't noticed any interference nor have I had to increase the squelch settings.

This seems to work well for a home based hobby scanner station, I certainly would never suggest it for a mission critical application.

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If it works for you, and you're happy with it, then that's what matters. Once an FM signal is in saturation, it doesn't matter how much stronger it can be made, or what the noise figure of the receiver system is. It's full quieting, end of discussion. It seriously matters, though, if you're trying to dig stuff out that's otherwise too weak to be usable.

If you ever get the chance to play around, but don't have a noise figure meter, you can make some sensitivity measurements with a SINADDER and a signal generator. You can try different configurations and make real measurements. You'll find it quite interesting how cascaded gain stages can misbehave if you let them.

Signal strength indicators (RSSI level) work on the limiter circuit of a FM demodulator. Limiters will respond to anything thrown their way. Intended signals, floor noise, crud that creeps past the IF filters, images and IMD, even looking at the radio cross-eyed (well maybe not) will swing that needle higher, so that should not be the ultimate deciding factor of a hot rod radio. What you need is signal to noise ratio.

You have definitely increased your signal. Now is the S/N a little better using quality amps or are you hosed using a cheap TV amp? Maybe you just lucked out that there are no high power pagers close to you, or NOAA weather, or maybe a TV station. In any case, if a preamp helps and you get no dire faults from it for what you listen to, great. For those wanting to stack preamp upon preamp to be the best receiving station in their neck of the woods, don't come crying when it works like crap.

As ZZ said, multicouplers should operate at unity to maybe a couple of Db gain. Don't force everything down your receivers throat. Use attenuators to smooth things out.

Acutally, shooting from the hip

gmclam said:

Your second solution is to feed your antenna into a passive splitter (think cheapo cable TV splitter) and feed each signal from that splitter into multicouplers. Yeah you get ~3.5dB of loss from that first split, but it will produce less issues.

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Seems the most logical to me...

I cascade two of the Stridsberg MCA208M's together like that.
What I've found is that it mostly works but where it fails is when monitoring P25 systems on scanners that are hooked to the 2nd multicoupler. The added noise from the two units destroys the P25 data on any scanner that is plugged into the 2nd multicoupler.
Now this is with P25 systems that already have a weak signal. Those that are close and have decent signals work fine on either multicoupler.
I blame it on the fact that the 2nd coupler is just doubling the noise that is produce internally within each coupler.
I did a test and used a passive Stridsberg 2 port coupler and fed the two outputs into each 8 port unit and then I had great P25 performance on both mutlicouplers.
I did end up going back to my cascded setup and only use the radios on the 2nd unit for conventional signals. That works fine and any extra noise is barely perceptible. I can detect it on weak UHF (450 MHz) stations though. That is by ear also. It is very evident on a weak P25 signal though. I also have a Digital Loggers Inc. 16 port multicoupler that sucked. By itself, it had enough internal noise that it destroyed all weak P25 signals. I also still use that unit but again, only for conventional VHF and some UHF stuff. The noise figure from that model is higher than the Stridsbergs combined so it is poor for digital signals unless they have a really nice signal level to begin with.
I'd love to find a 16 port model that does not add noise into a weak P25 signal but so far, I've not found anything cheap.
By cascading the two 8 port Stridsberg's, I've never found that combo to introduce any intermod or other undesirable signals other then the P25 killing noise.
Even John Stridsberg said it was not ideal to cascade them together. I talked with him about this very subject. He said it was better to use a passive splitter and feed the inputs from that instead.
In my eyes, if you have enough ports on the first multicoupler to handle all your digital radios, go for it but watch the weak 450 MHz signals. I do not reccomend cascading them if the 2nd unit will be used on digital systems although it seems to work on those that have decent signal levels.
You also need to watch the signal level that you are feeding into the multicouplers. Be careful if using a preamp in front of them.
I do feed one of mine with a 800 MHz preamp but I must attenuate that preamps output before it hits the multicoupler. I only use that setup for two weak P25 systems here. Stridsberg's preamps bypass when power is removed which is nice.
As was mentioned, you will just double the noise figure when you cascade two together. And that can be more than enough to confuse a scanner when it is attempting to decode a digital data stream.
I've also cascaded two of his 4 port HF models. I bought a 4 port never imagining I'd ever need that many ports. Now two four port models are not even enough. The noise figure on the HF models has never caused problem when cascading them. I'm not even sure I cascade my HF couplers any longer. I think I use a passive splitter now as it had better LW passthrough then the multicoupler allowed so I think I feed a R9000 off the passive splitter and then two of the ports feed each of the HF actice multicouplers. For the VHF and higher signals, the R9000 is fed from the 1st 8 port MCA208M coupler only.

ramal121 said:

Signal strength indicators (RSSI level) work on the limiter circuit of a FM demodulator. Limiters will respond to anything thrown their way. Intended signals, floor noise, crud that creeps past the IF filters, images and IMD, even looking at the radio cross-eyed (well maybe not) will swing that needle higher, so that should not be the ultimate deciding factor of a hot rod radio. What you need is signal to noise ratio.

You have definitely increased your signal. Now is the S/N a little better using quality amps or are you hosed using a cheap TV amp? Maybe you just lucked out that there are no high power pagers close to you, or NOAA weather, or maybe a TV station. In any case, if a preamp helps and you get no dire faults from it for what you listen to, great. For those wanting to stack preamp upon preamp to be the best receiving station in their neck of the woods, don't come crying when it works like crap.

As ZZ said, multicouplers should operate at unity to maybe a couple of Db gain. Don't force everything down your receivers throat. Use attenuators to smooth things out.

Click to expand...

I think you hit the nail on the head here. I am blessed that I have few overloading signals here and 95% of what I listen to is very local.

For now it works OK. I might try the other suggestion of a splitter before the multicouplers when I have time. I might also try and find some weaker signals to use as a measuring stick since I no longer have access to a signal generator.

Late to the party,as usual. I'm running 3 Electrolines inline.
Discone to basement where the shack used to be. Amp 1 (4 port 7db out) fed upstairs and two rooms in the basement. Shack moved to back bedroom upstairs. Jumper to Amp 2 in new shack feeding 8 port (4db out) that runs 2 106's 2 2045's a 600 and a 780XLT jumper to garage Amp 3 4 port so I can have digital 106 and 2045 for everything else.
RG6 from antenna and all jumpers.
780 is a "new" addition and I have to run the att for one railroad frequency. (FM station getting in)
Yes, they are drop amps. But it works. I have 400 ready to replace the feed from the discone to amp 1.

ind224 said:

I'm running 3 Electrolines inline.

Discone to basement where the shack used to be. Amp 1 (4 port 7db out) fed upstairs and two rooms in the basement. ... Jumper to Amp 2 in new shack feeding 8 port (4db out) that runs 2 106s 2 2045s a 600 and a 780XLT jumper to garage. Amp 3 4 port so I can have digital 106 and 2045 for everything else.

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This is a slightly different configuration than the OP has explained. Those runs between one amp output and another amp's input have some attenuation on them. Not sure I'd do this though.

If the OP wants to merely get more outputs from a single antenna by using multicouplers that have fewer outputs, I would split the antenna signal BEFORE the multicouplers with a passive splitter and feed into each amp rather than cascade one amp into another.

[No message]

It really comes down to what you are trying to achieve. Most scanner listeners are dealing with very strong signals whether they realize it or not. The in depth and detailed methods of analyzing system noise figure and dragging that last bit of antenna system performance out will not apply to 90 percent of people with a BC780xlt running on the computer desk, not that it doesn't matter but that you just cannot appreciate that kind performance in the way of telling a difference with most scanners. Others running better receivers are a different story. Dealing with fairly strong signals the negative effects of cascading the amplified multi couplers may end up being viewed as a positive by the high s meter readings. Not to mention everyone is in a different RF environment. Things I can get away with in rural country others would have tremendous problems with in more hostile RF environment. Bottom line if it works for what your trying to achieve then this wrong for others is a right for you. When you venture to hear things weaker and and weaker, DX if you will, all of the hard core details will become right for you then....