Multicouplers

[nessnet]

Is the MCA404M an earlier version of the MCA204M?

I have it right here.
MCA204M.
Typo... I am a pillock..

 

[dlwtrunked]

I do (understand).
Climbed trees up in the mountains to put amps and antennas as high as I could for VHF TV .
Familiar with the gear.

I conceded elsewhere.
People make the ED2800 work.
As long as they can make the 75 vs 50 work.
I should have looked before I posted - mia culpa.

I still will rely on my MCA408M.
Anyone need a MCA404M?

I hope you understand that the impedance argument does not work. The loss due to that impedance difference will not be noticeable as many posts over decades will show. In fact, the loss is around 0.2 dB if I recall correctly--this is a trivial loss. And even more significant is the impedance on the scanner is not flat nor is it likely to be exactly 50 ohms. In fact, some scanners have been measured as closer to 75 ohms. There is no good argument about the impedance here making a real difference. (And the loss of using an impedance matching circuit is greater that the impedance loss in all that I have seen.) Arguing for 50 vs. 75 ohm coax (of both are good coax) is wasting one's time. Of more importance is the NF for the amplifier among other things.

 

[RichM]

I run 3 SDR’s and 2 hardware scanners off my Electroline fed by a single discone. It works great for me, zero signal loss compared to direct connect to my external antenna. $40 bucks and rock solid dependability, been doing it this way for years. They really do work well for a fraction of the cost.

 

[prcguy]

I hope you understand that the impedance argument does not work. The loss due to that impedance difference will not be noticeable as many posts over decades will show. In fact, the loss is around 0.2 dB if I recall correctly--this is a trivial loss. And even more significant is the impedance on the scanner is not flat nor is it likely to be exactly 50 ohms. In fact, some scanners have been measured as closer to 75 ohms. There is no good argument about the impedance here making a real difference. (And the loss of using an impedance matching circuit is greater that the impedance loss in all that I have seen.) Arguing for 50 vs. 75 ohm coax (of both are good coax) is wasting one's time. Of more importance is the NF for the amplifier among other things.

For resistive source and resistive load you are correct!

But that doesn't work in the real world with a complex load on the receiver end and also on the antenna end and with other components in the circuit. Then different lengths of 75 ohm coax in an otherwise 50 ohm system can cause several dB of insertion loss. For example stick a 1/4 wavelength section of 75 ohm coax between two 50 ohm devices and it tries to be a 50 to 100 ohm matching device with anywhere from .5 to 5dB or more loss depending on circuit VSWR, inductance, capacitance, etc.

Everyone's setup is different and can't be easily estimated, it has to be measured to really know the complex impedances and the actual loss using 75 ohm coax in a 50 ohm system. Some people may get away with that elusive .5dB loss. Others might have 3 or 5dB loss from using a simple 75 ohm jumper and not even know it. That's why its ALWAYS best to use 50 ohm coax in a 50 ohm system to avoid unknown problems that will bite you.

Would you run a paint thinner/alcohol/acetone mixture in your car because someone on the Internet says it works fine? Same with recommending a mixture of coax impedances in the same system and its not fine.

 

[wa8pyr]

Basically a multicoupler but not really. Electroline is designed for a known number of carriers at a known signal level, which is not very high. The Electroline and similar units were never intended to connect to an antenna with an unlimited number of carriers at levels you can encounter off an antenna. In many areas like where I live they will overload on a Discone and create tons of IMD and ghost signals at many frequencies in addition to greatly raising the noise floor.

They might not be designed for it, but they do work well, at least in a suburban area. I’m not sure I’d trust any of these devices (Stridsberg or not) in an RF-dense urban area unless they were designed for it.

 

[prcguy]

They might not be designed for it, but they do work well, at least in a suburban area. I’m not sure I’d trust any of these devices (Stridsberg or not) in an RF-dense urban area unless they were designed for it.

That's why some of us build our own and this has an IP3 14dB higher than a Stridesberg, very effective FM broadcast notch and an RF limiter that will handle up to 10 watts at the input and clamp that to about 10mw to protect the amplifier. This one has since been modified with a higher gain amp and 8-way divider.

And there will never be a 75 ohm cable or device used anywhere near it.

 

[Ubbe]

I measured my BCD536 impedance at its antenna connector and between 118-137MHz it varies from 30 ohm up to 110 ohm. My Sirio airband antenna goes between SWR 1:1 to 2:1 in the airband and then 2:1 are either 25 ohm or 100 ohm in relation to 50 ohm.

To reduce the effect of impedance mismatch one can use an antenna amplifier between antenna and coax that will give a more constant impedance both to antenna and to the coax. At the receive end, at a scanner, one can use a splitter like a $5 CATV type that also works as a impedance buffer and also isolates outputs between each other to reduce interference but will also introduce a 3-4dB loss that needs the signal to first be amplified, either at the antenna or directly at the splitter that then becomes a multicoupler.

Adding an amplifier at the antenna will not only overcome coax and splitter losses but will also stabilize the impedance in the whole antenna system.





/Ubbe

 

[trimmerj]

Looks like they have gain to me...

View attachment 198430

Get the UG versions

 

[dlwtrunked]

For resistive source and resistive load you are correct!

But that doesn't work in the real world with a complex load on the receiver end and also on the antenna end and with other components in the circuit. Then different lengths of 75 ohm coax in an otherwise 50 ohm system can cause several dB of insertion loss. For example stick a 1/4 wavelength section of 75 ohm coax between two 50 ohm devices and it tries to be a 50 to 100 ohm matching device with anywhere from .5 to 5dB or more loss depending on circuit VSWR, inductance, capacitance, etc.

Everyone's setup is different and can't be easily estimated, it has to be measured to really know the complex impedances and the actual loss using 75 ohm coax in a 50 ohm system. Some people may get away with that elusive .5dB loss. Others might have 3 or 5dB loss from using a simple 75 ohm jumper and not even know it. That's why its ALWAYS best to use 50 ohm coax in a 50 ohm system to avoid unknown problems that will bite you.

Would you run a paint thinner/alcohol/acetone mixture in your car because someone on the Internet says it works fine? Same with recommending a mixture of coax impedances in the same system and its not fine.

I agree usjng 50 ohms is preferred but have never been able to measure a difference in reception in over 50 years. As I point out, scanners are not accurately 50 ohms. Nor are many scanner antennas so one is chasing an unknown. Note Ubbe's post in this regard.

 

[wa8pyr]

That's why some of us build our own and this has an IP3 14dB higher than a Stridesberg, very effective FM broadcast notch and an RF limiter that will handle up to 10 watts at the input and clamp that to about 10mw to protect the amplifier. This one has since been modified with a higher gain amp and 8-way divider.

And there will never be a 75 ohm cable or device used anywhere near it.

Nice!

I’m in the process of building something similar, à la N9JIG’s project ( Scanner Tales: Rolling my own (Multicoupler, that is) ). I’ve got all the parts (umpteen-port splitter, limiter, preamp, terminators for open ports, etc), just need to assemble it. Problem is, I’m in the process of a shack redesign and haven’t quite decided where it’s going to go and how to put it together yet.

Initially at least, I’ll need to feed it with 75 ohm quad-shield RG6, as that’s what runs to the antennas in the attic (a couple of Monitennas). My cable run to the attic is only about 25 feet at most, so if I could find a reasonably-priced amateur or commercial-grade antenna that covers VHF, UHF and 700/800 I’d go with that and feed it with RG8X. Otherwise I’ll stick with a Monitenna and the RG6.

I’ve never been too worried about using 75 ohm cable in a scanner application; impedance can vary quite a bit across 950+ MHz, making the difference between 50 and 75 ohms relatively inconsequential, and quad-shield RG6 has always performed well for me.

Update: Digging a bit deeper, looks like the DPD Omni-X might do the trick….

 

[dave3825]

I have the EDA2800 myself. Highly recommend, works great.

Same here, 8ports for scanner and sdr.

They might not be designed for it, but they do work well,

Kind of like the DBV-2 sticks were made for digital tv, but work well for sdr.