Multicoupler Question

[jbenoist]

Is a Multicoupler really necessary to run two scanners simultaneously on the same antenna?

 

[marksmith]

With or without, some signal loss will occur.

536/436/ws1095/996p2/996xt/325p2/396xt/psr800/396t/HP-1/HP-2 & others

 

[cpetraglia]

Not if you get an active multicoupler. If you have a really strong signal, you can get away with a simple TV ant. splitter, but there is typically 3.5 DB loss per output. If you look at a Stridsberg Active Multicoupler, you'll get a built in preamp that eliminates loss to the output. I use a few of them and they are very good quality devices. Quite pricy I might add.

 

[ofd8001]

Running two scanners on the same antenna will lead to signal loss.

One other consideration is the cost of the multicoupler. More often than not, the cost of a multicoupler exceeds the cost of a second antenna. So unless I was able to get on a real tall tower, thus having a very long cable run, I'd be tempted to get a second antenna.

 

[n5ims]

Is a Multicoupler really necessary to run two scanners simultaneously on the same antenna?

Really necessary? No. But there's a huge "but". Since you're basically connecting the two scanners together directly (using a "T" coupling, most likely) it will be without any isolation (the multicoupler includes isolation) you could easily have some signal mixing or other issues that will cause signals where they don't actually exist or other artifacts that may cause issues. You'll still have loss since the signal will need to be split between the two devices. The multicoupler splits the signal prior and then isolates the two sides from each other and prevents the internal signals from one scanner being fed to the other scanner. The "active" splitters mentioned add a preamp to the mix to eliminate the loss. This preamp may help or it may hurt (close or strong signals may overload the preamp for example) so it's not always a good thing.

Now some comments on loss. Sure, those splitters have about 3 dB or more of loss on each output and that's half the signal!!! Sounds bad, right? Well, it may not really matter. A scanner needs a certain amount of signal to work at all. The signal will be noisy, but still generally understood by your ears. With a certain additional level of signal the noise will be gone and you'll have a clear, noise free signal. This noise-free signal will sound the same over a pretty wide range of additional signal being sent to your scanner. Once you get to a certain level of signal you'll end up with too much signal for your scanner to properly handle and start having issues properly decoding the signal and will start having noise, distortion, and perhaps even drop-outs in the audio from your scanner.

While these numbers are not accurate, they will show you how loss can affect your scanner's reception (the exact numbers will vary on the design of the circuits used in the scanner and to some extent to the specific components in each scanner). Say the lowest level your scanner can detect is 3 units of signal. From 0 to below 3 units your scanner will only produce static noise, perhaps with some audio getting through as you get closer to the 3 unit level, but still not really pleasant to listen to. As you increase this level from 3 units to 7 units the noise gets less and less and the audio gets better and better. Once you pass the 7 unit level, you have great audio and no static noise until you reach the 40 unit level. Once you exceed the 40 unit level your scanner starts working weird, fine one second and noisy or distorted audio the next. As you increase this signal level above 40 units things just get worse and worse.

OK, we've plotted how your scanner signal level works, so lets further explain your setup. You generally monitor three local systems. One has a signal level of 32 units, one has a signal level of 28 units and the third is further away and has a signal level of 12 units. Based on the plot above, all will be received by your single scanner just fine with no static noise and great audio. So, you get a second scanner and a two output coupler that has 3 dB loss on each output. Your signal levels will now be half of the values listed so each scanner will get the systems at 16 units, 14 units, and 6 units. The result of adding that splitter with that huge half of your signal loss will result in the two strongest systems being just as good as without the splitter and the less powerful signal will move from no static and great audio to just a bit of static and still good audio. Should you spend the extra money on an active splitter to eliminate the bit of static on that system? That's up to you, it may or may not be worth the extra cost, depending on how bothersome that little hiss on the signal is to you.