Build Mini Circuits multicouplers or buy Sdridsberg?

[rabrol]

I currently have an Electroline 8 port drop amp. It feeds radios, and a Sdridsberg MCA208. Single antenna is a home-made dipole sitting in the shack, using RG6 coax right now. I'm feeding 6 scanners, 2 commercial radios (RX only), and 5 SDRs. 5 more SDRs going in the mix soon. Several other portable radios in the shack using their own "rubber ducks". It works, but I want to build something with less noise and good distribution.

Next month I'll be throwing a cheap Tram discone on the roof, along with a couple of home-made dipoles (770 MHz, Civ Air).

I'm tempted to buy another MCA208 or Electroline. However, reading through this section of the forum has opened my eyes to another possibility. Self-building for higher spec than Sdridsberg. Ubbe & PRCGuy have posted about this in multiple threads.

Goal would be to have a good multicoupler for 770 MHz. I would like to distribute to 3 SDRs and an SDS100. Am considering adding a BPF-800 inline, before the multicoupler as I have a cell site less than 1km from the house.

I'd like to distribute airband signals to 4 scanners and 2 SDRs (ACARS & VDL/2 decodes).

The generic discone will be used for VHF Hi & UHF (406-470), but I would consider using it as a primary antenna including civil airband / 700 MHz if it performs well enough.

I have dealt with BCB FM interference by adding a NooElec Flamingo FM Notch filter. That works a treat (although takes a bit too much off 118.300 - my local tower freq for my liking).

I have a strong pager at 139.950 MHz. This hits me hard when monitoring top end of airband & VDL/2 decodes. Open to suggestions on that one.

So my main question, given that I'm not very 'handy' or good at building things.
Is a Mini-Circuits type solution higher quality for lower cost than a Stridsberg? I'm presuming it would be streaks ahead of the Electroline as well.
For those who are familiar with the Mini-Circuits offerings, what would you build for what I'm trying to achieve? Which products? I'm thinking multiple 4 or 8 port solutions allow me to better filter stuff (e.g. add an airband BPF, or notch for 139.95, but still be able to decode WX sat & VDL), a 770 MHz band pass for the P25 radios etc).

Also, for RX only, I've been happier with RG6 than RG58. Is it really worth the additional expense of running LMR-400 for the main antenna feeds coming to the multicouplers?

All suggestions & comments gratefully received!

 

[iMONITOR]

I have a strong pager at 139.950 MHz. This hits me hard when monitoring top end of airband & VDL/2 decodes. Open to suggestions on that one.

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[Ubbe]

Keep in mind that at 150MHz the -10% are 135MHz and +10% are 165MHz. So probably not a filter that can be used for most cases.

/Ubbe

 

[rabrol]

I actually had Dale from PAR custom make a filter for me. Much better than +/-10%, but don't recall the actual figures.
Reception of VDL2 is fine, at 136.975. PAR were easy to deal with, and happy to custom make the filter.

So now it is on to the next part of the project. Snow is melting, and soon it will be time to get the antennas airborne and out of the attic.

I've picked up 2 x PGA103+ devices, and there is now a 120v power outlet in the attic. I'll run some kind of transformer to supply the PGAs with 5V. These will feed into a couple of passive TV splitters.

 

[APX8000]

I saw ZERO difference between my 4 port Stridsberg vs rolling my own with a Mincircuits 4-way splitter, PGA-103 LNA and notch filter. The benefit of rolling my own was I got everything cheap off eBay so the overall cost was less.

 

[Pape]

Curious, what part would be required from Minicircuits for the multicoupler ?

 

[dlwtrunked]

Curious, what part would be required from Minicircuits for the multicoupler ?

When you use any multicoupler, you have a loss in signal. An amplifier from Mini-Circuits or elsewhere can make up for that. The Stridsberg active multicouplers have such an amplifier, although they also sell passive (no amplifier) ones for when the multicoupler has a small number of outputs and thus the smaller loss of signal might be tolerated.

 

[prcguy]

Minicircuits sells good quality power dividers in all kinds of frequency ranges and number of output ports. For VHF/UHF you might consider the ZSFS-8-43 which is an eight output and covers 10 through 1,000MHz in 50 ohms.

They also have lots of amplifiers and for my RF hell area I would consider the ZFL-1010 covering 50-1,000MHz with around 10dB gain and a noise figure of 3.5dB, which is a bit high but close to what Stridsberg offers. However the high signal level handling of the ZFL-1010 is massive compared to the little amplifiers Stridsberg uses.

Some people have been using the ZX60-P103LN which covers 50MHz to 3GHz with a great .5dB noise figure, but its got more slope than I care for with the gain ranging from about 25dB @ 50MHz to 20dBdB @ 500MHz and 15dB @ 1GHz.

 

[Pape]

Minicircuits sells good quality power dividers in all kinds of frequency ranges and number of output ports. For VHF/UHF you might consider the ZSFS-8-43 which is an eight output and covers 10 through 1,000MHz in 50 ohms.

They also have lots of amplifiers and for my RF hell area I would consider the ZFL-1010 covering 50-1,000MHz with around 10dB gain and a noise figure of 3.5dB, which is a bit high but close to what Stridsberg offers. However the high signal level handling of the ZFL-1010 is massive compared to the little amplifiers Stridsberg uses.

Some people have been using the ZX60-P103LN which covers 50MHz to 3GHz with a great .5dB noise figure, but its got more slope than I care for with the gain ranging from about 25dB @ 50MHz to 20dBdB @ 500MHz and 15dB @ 1GHz.

When you say "slope" you are referring to the amplification db number reducing with frequency ?

 

[prcguy]

When you say "slope" you are referring to the amplification db number reducing with frequency ?

Yes, ideally you have a little more gain at 1GHz than at 100 or 50MHz to match the attenuation slope of your coax so that everything arrives at your radio closer to how it arrives at your antenna.

 

[Ubbe]

You can insert a small capacitor in series with the signal. If not bothered too much about impedance match it can be inserted anywhere but ideally it should be in a circuit that has a 50 ohm resistor to ground and then in series with the signal a 1k resistor with a 4,7pF capacitor in parallel and after that a 50 ohm resistor to ground. It would introduce a 10dB loss at 50Mhz compared to 1GHz.

Usually you will have to add additional attenuation when using an amplifier, maybe 10dB, so perhaps a slope capacitor circuit can be built into that attenuator, or in a splitter, or that 1k resistor can be a 2,2k one and use a capacitor with a lower value to give the desired attenuation.

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/Ubbe

 

[prcguy]

You can insert a small capacitor in series with the signal. If not bothered too much about impedance match it can be inserted anywhere but ideally it should be in a circuit that has a 50 ohm resistor to ground and then in series with the signal a 1k resistor with a 4,7pF capacitor in parallel and after that a 50 ohm resistor to ground. It would introduce a 10dB loss at 50Mhz compared to 1GHz.

Usually you will have to add additional attenuation when using an amplifier, maybe 10dB, so perhaps a slope capacitor circuit can be built into that attenuator, or in a splitter, or that 1k resistor can be a 2,2k one and use a capacitor with a lower value to give the desired attenuation.

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/Ubbe

You would want to do this after the amplifier, otherwise any loss will directly add to the noise figure.

 

[Pape]

As it stand currently the slope is not much of a issue for me. I guess the question is how much lost I need to account per port so the amp is properly sized

 

[prcguy]

As it stand currently the slope is not much of a issue for me. I guess the question is how much lost I need to account per port so the amp is properly sized

A two way divider has about 3 to 3.5dB loss, a four way about 6 to 6.5dB and an eight way 9 to 9.5dB. Its nice to have 1 to 2dB extra gain, so you you should be able to figure out what amplifier gain to use and/or how much to attenuate after the amplifier. You wouldn't want to get a 20+dB gain amp just to feed a two way divider, etc. A 10dB gain amp should be fine for anything up to an eight way divider.

I would pay close attention to IP1 and IP3 ratings and try to get something with at least 20dBm IP1 and 36dB IP3 and noise figure under 1dB.

 

[Pape]

Also need to account for any other insertion lost and coax as of currently I have 75' of lmr-400 that account for 4 DB lost
Indeed, understanding my NF is currently the task at hand

 

[prcguy]

Also need to account for any other insertion lost and coax as of currently I have 75' of lmr-400 that account for 4 DB lost
Indeed, understanding my NF is currently the task at hand

You can put the amplifier at the antenna and more than make up for feedline loss. Then it can feed the same splitter at the radio end.

 

[Pape]

Exactly, need to account for all insertion lost after the LNA including the coax