BIAS-T Powered Pre-AMP

[cmed325]

My question is two parts actually, 1. What is a tried and true Wideband Pre-Amp that would be Mast Mounted and fed by a Bias-T
2. The Coax will go into a Stridsberg 8 Port Multicoupler,,I live in a gully and need all the help i can get with reception,,Any suggestions?

 

[Ubbe]

Any suggestions?

A PGA103+ based amplifier will be unexpensive and have an incredible good cost/performance ratio. The different amps available have the exact same specifications and the difference are how they are enclosed and what connectors they use and also have they are powered. Just make sure that it can be powered from the coax. It's just an extra 10 cent choke coil on the circuit board that can be easily added to any amplifier, but it helps if its already in place.

A Bias-T are just a box that the coax goes thru that has a choke coil, just as the amplifier, to isolate RF from DC and a couple of capacitors, less than a dollar in component cost but for some reason they are overly expensive and could be due to they are often specified to work up to 5000MHz and at that frequency it's important with a coils stray capacitance and a capacitors stray inductance that could create self oscillation if too cheap components are used at GHz frequencies. When doing one yourself just cut a coax and splice the ends and add a coil and a capacitor and a power cable and isolate with tape and put in a metal box. Or get a CATV 2-way splitter with power pass and stick a coil connected to a power source in one of the ports.

Amplifiers usually needs attenuators to bring down the signal to a level that do not overload a receiver/scanner. Stridsbergs multicouplers could be a bit sensitive to strong signals and needs carefully matched signal levels. Using a variable 20dB attenuator makes it easy to find the sweet spot.

/Ubbe

 

[prcguy]

I would use a good preamp with enough gain to overcome an 8-way passive divider and not use a Stridesberg. Using a broad band preamp with a broad band antenna can be a disaster in some areas. I would consider a PGA103+ based preamp on the very low end of the scale and a MiniCircuits ZX60-P103LN has very low noise figure, about 25dB gain in the VHF band and about 15dB gain at 800MHz, not ideal but workable. Here is a data sheet on the preamp. Mini-Circuits

An 8-way passive divider has 9 to 10dB of insertion loss. You only need enough gain to make up for that and maybe a little feedline loss so you might end up using an attenuator after the preamp. It would be great if there were a lossy equalizer with a matching slope to bring down the gain at VHF without affecting 800MHz, but I have not found one. I would also recommend a good FM trap filter and the MiniCircuits ZBSF-95-N is the best I have found. Here is a data sheet on that. https://www.minicircuits.com/WebStore/dashboard.html?model=ZBSF-95-N+

For Bias-Tees you can go with MiniCircuits but they can be pricy. I've used several Chinese models off Ebay and they have been very good for low $$. Here is one version. RF Translator Broadband Radio Frequency Microwave 10MHz-6GHz Bias Tee with Case | eBay

You would probably end up building the amplifier in an outdoor NEMA rated box at the antenna and I would feed 12 volts up the coax using the bias Tees then use a 12 volt to 5 volt 3 terminal regulator in the box at the antenna since the amplifier runs off 5 volts.

 

[merlin]

My mast mount preamp is Scientific Atlanta 750515C drop amp. 15Db gain 1.2 Db noise 50 Mhz > 1200 Mhz
$5 on ebay.
Typical SDR won't power it (3.3V) takes external inserter and 10>16V.
I use switches for 2 antennas, DiSeqe control in front of that.
45' RG6QS to a preselector with 0>30Db attenuation,band pass filtering, another 10Db gain stage then to the receivers.
The SA drop amp will certainly do you justice.

Scientific Atlanta Surge-Gap Drop Amplifier 5-40/51-1000MHz # 750515C | eBay

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Spares I have on hand:

 

[Ubbe]

It would be great if there were a lossy equalizer with a matching slope to bring down the gain at VHF without affecting 800MHz, but I have not found one.

Open up the bias-T and add a 10 cent 2.7pF capacitor in line to the output to the receiver. Put a 10 cent 330 ohm resistor in parallel to not attenuate low-vhf too much. Use an online reactance calculator and if needed a total resistance parallel resistor calculator and try different values for capacitor and resistor to find a suitable slope when loaded by a 50 or 75 ohm splitter. Connecting directly to a scanner will give unpredictable results as a scanners impedance are not at a fixed value and changes with the frequency inside the scanners frequency range for its band filter .

Getting rid of the Stridsberg are a good solution and instead use a passive CATV 75 ohm splitter are no problem as any small impedance mismatch do not matter when having a preamp. I use a PGA103+ with a 1-6 CATV splitter and coax that has no more than a 3dB loss and any modern scanner I have can handle that signal level, but then I live in a weak signal location.

/Ubbe

 

[cmed325]

Thank you for all the great suggestions, I have two new Bias-T,s,,,I need a Pre-Amp that will work with one,,Probaly mountred at the Antenna which is up on roof? Theres been many other suggestons that are way above my expertise thats why i need easy suggestions that work to improve my reception,,Yes i run LMR 400 ETC,,I run many radios off my 8 Port Multicoupler,,

 

[merlin]

Open up the bias-T and add a 10 cent 2.7pF capacitor in line to the output to the receiver. Put a 10 cent 330 ohm resistor in parallel to not attenuate low-vhf too much. Use an online reactance calculator and if needed a total resistance parallel resistor calculator and try different values for capacitor and resistor to find a suitable slope when loaded by a 50 or 75 ohm splitter. Connecting directly to a scanner will give unpredictable results as a scanners impedance are not at a fixed value and changes with the frequency inside the scanners frequency range for its band filter .

Getting rid of the Stridsberg are a good solution and instead use a passive CATV 75 ohm splitter are no problem as any small impedance mismatch do not matter when having a preamp. I use a PGA103+ with a 1-6 CATV splitter and coax that has no more than a 3dB loss and any modern scanner I have can handle that signal level, but then I live in a weak signal location.

/Ubbe

A bandpass filter in line solves all of that. Too much gain and an attenuator fixes things.

 

[cmed325]

Not sure if this will help, Thnx for the advice.