my TV preamp scanner surprise...

[rjvalenta]

not sure if this is the right forum for this, but i thought i'd pass this along because i hadn't seen anyone mention this before.

i'm trying to feed 4 scanners from my roof Tram discone. the feed comes in to my attic and splits off via multiple SMA pigtails to an SDRDuo, down a 20ft 50ohm cable my old Pro197, then on to 75ohm cable to an old MR8100, and an RTLSDR stick... reception has been... meh. SMA splitters and a lot of adapters, and even a fork from a 50ohm split SMA cable to an old piece of 75ohm coax to the basement... the guys who tested me for my Amateur General license would be offended.

i needed to clean things up, so after some research i ordered a Stridsberg multicoupler... but it hasn't shown up and i've had no reply to my email, and some research here caused me to realize that while the company is apparently still producing amazing products, they are going through some restructuring and that's causing shipping delays and communications issues.

so i'm thinking about other options in the short term... searching online... and the guy who runs Frugal Radio mentioned how he used a CATV amp... and then i started to think about the Channel Master Titan 2 that I had in my attic that i had to remove from my OTA TV feed because it was overpowering my TVs (I'm too close to local TV towers to use it).

so i tried it... pl259 to type F into the Titan 2 with a 75ohm jumper cable... then a 75ohm jumper into the SMA pigtail splitters - still a mess!

but... it seems to have worked.

it's a mess, but i'm hearing way more traffic from my airport instantly, picking up VHF traffic from dispatchers louder and clearer, i can't say it's 100% effective yet and i will definitely be replacing all the splitters etc when the multicoupler arrives, but i'm a little surprised this idea isn't more common. the 54 - 700 MHz range is definitely going to be an issue with local trunked systems, but i know channel master has made preamps that go to 1000Mhz - and they aren't expensive when compared to systems like Stridsberg.

how did i miss this??

does anyone else have inexpensive hacks like this that i should be using?

love to hear any thoughts, thanks.

richard

 

[vagrant]

An Electroline EDA-UG 2402 (54-1000 MHz) will split to four feeds. That particular model does not add gain, nor the potential noise along with gain. If you need eight ports there is the EDA-UG 2802. Some people will **** all over using 75 Ohm splitters and in fairness, not all splitters are the same. I urge people to test with an SDR, or better, so they can see some numbers/levels of gain, noise floor, etc. with that 2402 75 Ohm splitter inline...and then test again with the coax feed direct to the SDR without splitting it off. Experimenting is fun!

https://electroline.com/fact_sheets/eda/950-0013_EDA-UG_fact_sheet.pdf

* You may want to review the FM broadcast filter thread URL below in my signature.

 

[popnokick]

Actually no revelation in this. Here is one of several RR threads on this topic and others who have done it -
Combining a Scanner Antenna with a TV antenna into a single coax cable

 

[gmclam]

In lieu of a Stridsberg, I have a setup that goes like this:
- LMR-400 equivalent from antenna, with an N connector on it
- A couple of adapters to get from N to SMA to connect to a "lightning arrestor".
- SMA on the "lightning arrestor" to BNC to connect to a band stop filter.
- Band stop filter removes AM & FM broadcast (the strongest signals I get).
- BNC to F connector which connects to input of amplifier.
- Amplifier is low noise wide band with F connections in and out.
- Amplifier output is connected to high quality TV splitter (low insertion loss & passes up to at least 1GHz)
- Each splitter output connects to low loss RG6 (with F connector on one end and BNC on the other)

Sounds very similar to what you're doing. While a Stridsberg replaces some of the above, it still doesn't handle the lightning arrestor nor removal of the commercial radio broadcast bands.

 

[Ubbe]

love to hear any thoughts, thanks.

If it overloaded your TV then think about what it will do with your scanners. It has 26dB gain, way too much for any scanner.
It can't be more than 5-10dB coax loss in total and then two splits with maybe 3dB loss each with a total of 16dB. So perhaps a 10dB attenuator could be used to each receiver.

But best would be to use a variable attenuator of 0-20dB to each scanner, or at least dial it in at one scanner/receiver to get the best signal/noise ratio and count the number of turns on it and write down. Then try the next receiver and count the turns on the attenuator where you get the best signal/noise ratio. Then perhaps it turns out that the attenuation needed are not that different for all receivers and it can be placed before that first SMA split.

Having too much gain are the mistake most people do and then states that amplifiers can't be used and will only amplify the noise, like it did to your TV.

I have tried and used $5 inline CATV amplifiers up to $400 dollars ones in places that can be called RF hell and all improves reception with a single coax and scanner when their proper signal levels are tuned in and of course so much more if there are coax and splitter losses and even more if different band stop filters can be used. All scanners have bandpass filters for different frequency bands that perhaps attenuates up to 3dB-4dB that you will overcome when using an amplifier.

/Ubbe

 

[dlwtrunked]

...

how did i miss this??

does anyone else have inexpensive hacks like this that i should be using?

love to hear any thoughts, thanks.

richard

This has been done for decades. I remember first doing this 50 years ago (I am 70). But as others will surely post, you have to be careful with gain as UBBE has already noted. And often filters are needed. Individual situations vary. It is a balance between the receiver S/N, amplifier S/N (which needs to be better and enough gain to matter), receiver overload, nearness of strong stations requiring filters to deal with them, and *doing this every so often again as things change*. This is not just "plug-n-play" if one wants best reception but becomes almost its own hobby but hopefully not a time consuming one. Personally, I buy component pre-amps chosen for their noise figure (which is usually better than you have in your device) and chosen for gain and then compare against what I already have (and own a small fortune of filters). but most will not want to spend the amount of money regularly doing this. And what Vagrant said is so very true, using an SDR will really tell you a lot about what is going on in your antenna/amplifier chain. (Not using an SDR to do this is equivalent of being blind.)

 

[bearcatrp]

Stridsberg makes some pre amps. Ubbe, are these any good?

 

[Ubbe]

Stridsberg makes some pre amps. Ubbe, are these any good?

Yes, they are a quick and easy solution, plug and play with standard BNC connectors.

They are bit expensive and their performance are not among the better ones. There are $25 preamps with PGA103+ that are way better but then they usually use SMA connectors that will come loose easily if not using locktite and you have to arrange a local power source or add power thru the coax using a bias-T adapter.

Stridsbergs multicouplers have its amplifier in the splitter but it's better to set a preamp at the antenna and then have a passive splitter at the scanner end of the coax to also compensate for coax and connector losses and to load the coax with a constant impedance as most antennas will change impedance a lot over the frequency ranges used by a scanner.

/Ubbe

 

[gmclam]

Stridsberg makes some pre amps. Ubbe, are these any good?

And the OP's first message includes:
> i needed to clean things up, so after some research i ordered a Stridsberg multicoupler... but it hasn't shown up and i've had no reply to my email,

 

[bearcatrp]

And the OP's first message includes:
> i needed to clean things up, so after some research i ordered a Stridsberg multicoupler... but it hasn't shown up and i've had no reply to my email,

They make both!