TV amp for scanner

[ATCTech]

There is no intentional gain in a true multicoupler beyond amplification to overcome the splitting of the input signal to the output ports. Properly designed, they will not add RF noise because of their own internals, create mixing of various strong RF signals at their input or allow RF by-products developed in whatever devices are connected at their outputs to get back into their circuitry and therefore potentially affect the other connected devices. The entire idea of a multicoupler is to be "RF invisible" to all of it's connected devices. TV sets and related consumer devices really don't care about that because the source signals are individually so strong to begin with that the viewer will never see the RF artifacts created, analog or digital, unless they happen to live near a location like the CN Tower where the RF levels are horrendous. (Try designing/maintaining the ATC radio system at Toronto City Centre airport to meet required ICAO specs with that tower in the back yard and you'll know what I mean!)

If you want an amplifier with a $2 4-way splitter hanging on it's output then buy a TV amplifier and best of luck. If you're trying to share a clean airborne signal between multiple effectively isolated receivers then do it once and do it right. It's your money. A better antenna set-up and better feedline will win the race in all but the most RF isolated locations. In my days at Radio Shack in the late 70s/early 80s I'd estimate that 1 in every 2 of these 4-port amplified splitters we sold came back because they made the situation worse, adding more noise, bleed-through and intermod to the TV signals (particularly bad when installed on old analog cable TV of the day) than they cured. We used to keep one "open box", sell it to the customer and let them try if. If they liked the result we'd swap them for a brand new unopened unit. If they returned it then we didn't have a bunch of discounted inventory sitting around, it truly was that bad and a brilliant pre-emptive move on our part.

Trust me, we had exactly ZERO "pre-amps" of any type in any ATC receiver equipment and we checked the bandpass, linearity, input to output gain/loss figures and signal to noise of our multicouplers as part of preventive maintenance. Yes, we used multicouplers to allow one receiving antenna to feed on equipment rack of individual receivers in all of our larger radio sites. And no, the corresponding transmitters were not co-located in the same site or nearby.

I get that this is a hobby to most people here and I'm all for experimentation, I did it myself for years as I learned. But once I was introduced to and trained in actual safety-driven electronics in the ATC environment, I quickly realized the errors of my ways and out the door went all the junk radios, binder-twine cables, cheap connectors and no-name bits and pieces.

In this case, the juice is worth every penny of the squeeze to do it properly. My tagline says it all.

Cheers!

 

[Ubbe]

Are we buying the audiophile equivalent of the $400 IEC power cable?

Stridsberg are a profit making company and do not sell their devices at cost price. For $200 you get a nice aluminium box with connectors and a power supply. You connect the power supply and the coax from the antenna and the coaxes to your scanners and you're up and running after 2 minutes.

Its performance are moderate and you can do better if you have the time to source the equipment and the skill (not much needed) to connect them together. Stridsberg has 3,5dB noise figure and P1 of 12dBm and IP3 of 25dBm in it's amplifiers but you can get a $30 amplifier with much better 0,5dB noise and P1 of 22dBm and IP3 of 40dBm and a $5 CATV splitter that has 15-20dB isolation between ports. Add a 5Volt USB charger and the necessary coaxes with the correct connectors and you are done in an hour or two when spending time on Ebay/Amazon and then putting it together. You will end up with a higher spec multicoupler at 1/3 of the cost. It will not look as good as Stridsbergs device but you can always hide it away out of sight and it will be so easy to put that amplifier direct at the antenna and add a bias-T to overcome any kind of coax losses. Stridsberg also has remote amplifers and passive splitters but their solution will cost you more than $300 and at a poorer performance. But again, Stridsberg comes in neat little boxes that are pleasing to the eye and are plug&play.

/Ubbe

 

[kmartin]

I have one of these. It has a filter that blocks the 700 MHz range, so on mine I've noticed a big drop on my signal strength meter when monitoring my local trunk system. I would normally get full strength without the amplifier but only 2 bars with the amplifier.
However works well on VHF and UHF.

 

[gary123]

I use preamps a lot professionally. I agree with ATCTech. Do it once, do it right. We run the antenna through a single bandpass cavity then to the amp then to a proper splitter then to the receivers. All the cables are Heliax and N connectors where possible. Yes, we even have a lightning protector on the line.

For my personal use, I have the following amps available VHF 136-155, UHF 400-430 and 850-870. I don't use them often as I literally live right under the local tower. I do have several cavities that should I be interested in something I can band pass and feed to a receiver.

Remember the configuration for a amplified set up is antenna-filter-amp-splitter(optional)-receiver. If you put the amp before the filter the filter cannot remove what's already there (amplifier noise) on the freq's your interested in.

Having said all that, for many of you having a preamp available is a excellent option. You don't have to use it, but having it available is worth it. Even a broadband amp like the cable amps being discussed can be highly effective if you can get some type of filtering on them. This is not as hard as it sounds.

There are a ton of old duplexers and cavities on auction sites. Tuning them is remarkably simple. In many cases its a matter of 'pushing' the plunger until you can hear the signal. Again, there are many here on the forums who can assist in this. The critical thing to bear in mind is the more cavities the narrower the band pass.

If your wondering what to use as your signal source look for a control channel near the freq's you want to amplify and then adjust for maximum signal. and yes there are inexpensive ways to notch out a strong local signal (pager type thing).