Coax Type Suggestions ?

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BOBRR

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Hello,

Have a new Uniden BCD 436 hand held scanner.
Goes up to beyond 800 MHz, apparently.

Have a Scantenna in the attic, which I used many, many years
ago for a scanner I had then.
Not sure what kind of coax I ran from it, as it's all thru the walls, and I'm a bit on
the elderly side now to be climbing around and looking.
But, it's a fair guess, that it was a high quality coax, and picked for low-loss.

Terminates in my living room into a wall jack.

Question: for my new 436, I would like to hook into the wall jack to use
the attic Scantenna.

So, I guess I am looking for recommendations for what coax to buy for
this extension (wall jack to unit)..

Run would be about 15 feet from the wall jack to the handheld scanner, allowing
me some convenience in moving the scanner around while I'm sitting in a chair.

Also, this coax extension would have to be very small, and flexible;
*a Very small diameter wire.

And, of course, low loss for this 15 feet (up to 800 MHz +).

Suggests would be most appreciated.

Thanks,
Bob
 

jonwienke

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RG-6 would be your best bet. It's not super-small diameter but it's flexible enough that it's not going to break the scanner. It's what I use when I run my 436 as a base, with a 90-degree F-to-BNC adapter so I can have the scanner upright while the coax runs horizontally away from the scanner.
 

BOBRR

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From OP

Hi,

Thanks for help.
Very nice of you.

a. Do I want 50 ohm or 75 ohm ?

b. Will try your suggestion, but might you have any
thoughts for a really small dia coax thst would also be suitable. ?

Thanks
Bob
 

wa8pyr

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RG-6 would be your best bet. It's not super-small diameter but it's flexible enough that it's not going to break the scanner. It's what I use when I run my 436 as a base, with a 90-degree F-to-BNC adapter so I can have the scanner upright while the coax runs horizontally away from the scanner.
RG-6, and preferably the better quality stuff, double-shielded with at least 95% braid as well as the foil shielding. I've got 25 foot runs of this from scanner antennas in the attic to the second-floor office and it works very nicely.

Home Depot has 15 foot runs of this with the F connectors already assembled for about $8.
 

jonwienke

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ill try your suggestion, but might you have any
thoughts for a really small dia coax thst would also be suitable.
The small coax tends to be very lossy at 800MHz.
 

BOBRR

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From OP: A Bit Of Clarification, Please

Hi,

Some clarification from all you antenna experts.
I'm surely not.

The BCD 436 specs say it has a 50 ohm antenna
The Diamond antenna I would like to try also says 50 ohms.

The Scantenna in my attic is 75 ohms

"A 300 to 75 Ohm matching transformer is supplied. A 50 foot RG-6 coax cable with an F connector at
each end is supplied".

RG 6 is 75 ohm.

The long run from the antenna in the attic to my downstairs wall jack is undoubtedly 75 ohms.

So, for my (only) 15 foot run from my wall jack to the radio, is it more important to match the 50 ohms
spigot on the 436, and on the Diamond antenna, or go with 75 ohm coax (the Scantenna and the interior RG-6 interior wall run) ?

Why ?

For 15 feet, does it make any difference, probably ?

Any difference at the 800 MHz freq's ?

Educate me, please.

Thanks,
Bob
 

cmdrwill

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The Scantenna and RG6 will be just fine. Many here on RR are using RG6 for receivers without any problems.
 

popnokick

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Matching coax impedances on scanning receivers is not critical. It comes into play when you are transmitting, but by definition receivers don't do that. You'll be fine with 75 ohm RG-6 coax... and it is probably what you have in the wall coming down from the Scantenna. I use 75 ohm RG-6 from my attic antenna to three wall jacks connected to scanners in my house. Works great (all Uniden BTW). The manuals all say the antenna input impedance is 50 ohms.... but it simply doesn't matter whether 75 or 50.
 

c_snyder

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I was going to say if you wanted to match impedance there are plenty of places online that would sell you a custom length of lmr195 or lmr240 with ends installed for cheap.

Although RG6 would work fine as already noted.
 

majoco

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Also, this coax extension would have to be very small, and flexible;
*a Very small diameter wire.
RG6 is none of these things, especially the quad shield.

For a length of 15 feet RG174 will be fine, small and flexible, stranded inner, I know it will lose 8dB per 100ft but 15feet? - you won't notice any difference. Diameter - 0.11inch. You can get cables made up but you have to be very sure what plug you want on each end.
 

Ubbe

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Search in ebay for RG174 or even better RG316 and choose a suitable lenght (maybe need to connect two cables together) and connectors. You probably have BNC or PL female in the wall and you'll have SMA female on the BCD436 scanner.

A 10 feet RG316 with SMA costs $5

/Ubbe
 

KR3LC

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RG6 is none of these things, especially the quad shield.

For a length of 15 feet RG174 will be fine, small and flexible, stranded inner, I know it will lose 8dB per 100ft but 15feet? - you won't notice any difference. Diameter - 0.11inch. You can get cables made up but you have to be very sure what plug you want on each end.
At 800 MHz the best RG-174 has losses around 22 dB per 100 feet. So 15 ft of this stuff will have a loss of about 3 dB. A small loss but it can make a difference on fringe signals.
 

chief21

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NOTE: A loss of 3 dB is half the signal. IMHO, that's a lot of loss for a jumper. Better to use RG6 for most of that 15' length and only a short length of the very small coax to connect to the scanner.

John
 

LulaNord

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Hi...as per my knowledge receivers is not critical. It comes into play when you are transmitting, but by definition receivers don't do that. You'll be fine with 75 ohm RG-6 coax... and it is probably what you have in the wall coming down from the Scantenna. I use 75 ohm RG-6 from my attic antenna to three wall jacks connected to scanners in my house. manuals all say the antenna input impedance is 50 ohms.
 
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