4 recceive radios on 1 antenna

[brin831]

i am looking at setting up a number of mobile radios cdm 750's as receive only radios ... but want to couple their antenna feeds to a single receive antenna ... probably a directional yagi ... was looking at a 7.2 db gain antenna ...

any recommendations on a multicoupler to feed the various radio's ... was looking at this model MCA208A had read a few recommendations about it on here ...

couple things i was worried about ...

1. is it possible to "overgain" a radio?? ... i am only looking at about 75 ft coax run to antenna with a high quality rg8 low loss cable aprox. 2.1 db loss over 100 ft.
2. will this provide enough isolation if i am running 4 to 6 radios all within the 450-470 mhz range

thanks!!

 

[zz0468]

couple things i was worried about ...

1. is it possible to "overgain" a radio?? ...

Yes. I don't think the MCA208M will do that, though.

i am only looking at about 75 ft coax run to antenna with a high quality rg8 low loss cable aprox. 2.1 db loss over 100 ft.

Ok. It's rated noise figure is 2.5 db. Add 2.1 db of coax loss on it, and your system noise figure will be closer to 5 db. Starting to get cruddy, but still better than most scanners.

2. will this provide enough isolation if i am running 4 to 6 radios all within the 450-470 mhz range

Yes.

 

[brin831]

any suggestions as to a way to improve this type of setup under the constraints of a single receive antenna and aprox 75 feet of cable ... obviously a better line, shorter run could improve loss

any suggestions on a better multicoupler, also what should i use for short jumpers between the radio and multicoupler ... probably only 3 feet at most ... if that

thanks !!

 

[zz0468]

any suggestions as to a way to improve this type of setup under the constraints of a single receive antenna and aprox 75 feet of cable ... obviously a better line, shorter run could improve loss

any suggestions on a better multicoupler, also what should i use for short jumpers between the radio and multicoupler ... probably only 3 feet at most ... if that

thanks !!

1. Better quality feedline.

2. Read up about noise figure and low noise preamplifiers.

3. In the case of the multicoupler you specified, don't worry about the cable AFTER the multicoupler. The length and loss is is almost completely insignificant (within reason).

 

[trooperdude]

any suggestions as to a way to improve this type of setup under the constraints of a single receive antenna and aprox 75 feet of cable ... obviously a better line, shorter run could improve loss

any suggestions on a better multicoupler, also what should i use for short jumpers between the radio and multicoupler ... probably only 3 feet at most ... if that

thanks !!

Yes.

Hard line coax would help. Especially at UHF.

Use an extreme low-noise amplifier--- like something from Angle Linear. $$$

For one receive system I have on a hill, I use an 18db gain ultra low-noise pre-amp into notch cavities (to get rid of the paging crud), and then into a simple minicircuits multicoupler.

At the end of the line with all of the connectors, patch cords, non-amplified multicoupler, etc. I get about 4-5 db of FILTERED gain into the receiver port.

Remember adapters/connectors (even the silver ones) are BAD. You get about a 1/2 a db of loss for every connector and adapter you use in your system.

Use good quality coax, keep them short. Use Quality connectors, no China junk.

Shop around.

None of this has to be expensive.

 

[zz0468]

Remember adapters/connectors (even the silver ones) are BAD. You get about a 1/2 a db of loss for every connector and adapter you use in your system.

Generally good advice there, except for this.

For the purposes of this post, I just got done sweeping a handful of connectors on the network analyzer, with the intention of dispelling this myth that connectors and adapters are inherently bad.

I swept Type N, SMA, BNC, and type F connectors. I used mediocre grade connectors, nickle plated, not silver. Center pins are all gold plate.

In all cases, loss through a pair of mated connectors did not exceed 0.1 DB until frequency was raised above about 1.5 GHz. Obviously, SMA connectors performed best, with N's, BNC's, and F's falling in that order. F connectors were usable to above 3 GHz before loss and VSWR became an issue.

My premium grade silver and gold plated connectors and adapters measured about the same at 1 GHz. their

For receive purposes, particularly in FM modes, it would take well more than 3 db to detect the difference by ear.

So, it's probably safe to say, adding a decent quality adapter or connector as necessary is simply not a problem below 1 GHz. If you need to, just do it, and don't worry about the loss. It's insignificant.

 

[brin831]

ok so as a follow up what style of N connectors do you prefer the crimp or solder ?? same for bnc

 

[zz0468]

ok so as a follow up what style of N connectors do you prefer the crimp or solder ?? same for bnc

Depends. Do you want to plunk down $100+ for the crimp tool? Then the crimp connectors go on faster. Sometimes I prefer to use the solder/clamp type because they can be reused or repaired if they get damaged.

Performance wise, it doesn't matter.

 

[brin831]

well i actually already have a crimp tool to use so not an issue with the amount of video i've done spent the money long ago to get a nice tool and just about every die i could get for it soooo

begs to question best durability etc... if you could use either what would you use what would u prefer ... because like i said i'm looking at using rg8