Best small diameter coax for VHF/UHF
Curt Phillips
I have a situation where I cannot use a large diameter coax cable for a 2
meter radio and a scanner.
There will be about a 50' run from the scanner to the antenna and about a
50' run from the 2 meter radio to the antenna.
Since the larger diameter 9913 type cables can't be used, which is the best
choice among the small diameter cables?
It doesn't have have to be the same cable for both applications. I seem to
remember reading about some small diameter 75 ohm cable
(maybe from a cable TV application) that does a reasonably good job in
scanner applications. Perhaps that would be the best choice for the
scanner.
Your replys are appreciated.
73,
Curt W4CP
cphi...@engineer.com
Gary Coffman
You can try RG-8X, also called mini-8. This is a foam insulated 50 ohm
cable about the size of RG-58. The loss is higher than RG-8, but less
than RG-58. Radio Shack carries it.
A common CATV 75 ohm cable would be RG-6. Its loss is a bit less
than RG-58, but the mismatch may make it worse in practice. I'd stick
with 50 ohm cables in a 50 ohm system unless there was a compelling
reason to use a different impedance.
Gary
Gary Coffman KE4ZV | You make it |mail to ke...@bellsouth.net
534 Shannon Way | We break it |
Lawrenceville, GA | Guaranteed |
Graham Seale
In message <69eqv7$b...@bgtnsc01.worldnet.att.net>
cphi...@engineer.com (Curt Phillips) wrote:
> I have a situation where I cannot use a large diameter coax cable for a 2
> meter radio and a scanner.
>
> There will be about a 50' run from the scanner to the antenna and about a
> 50' run from the 2 meter radio to the antenna.
Since you want to use a scanner (ie Rx usage), one obvious soloution
is to use a low noise preamp at the antenna. The noise figure, of the
whole system is then mostly decided by the preamp, making the cable
loss much less important, and allowing you to use thinner more lossy
coax.
Calculate the coax loss at the frequencies of interest. However many dB
loss you find adds directly to the front end noise figure - unless of
course, the "front end" happens to be a preamp out near the antenna.
To hear a signal at all, it needs to be a bit above the noise floor!
73's & Good luck
G4WNT
--
Graham
Real address is gra...@southlin.demon.co.uk
Robert Harris
For a scanner application with small diameter coax, I would use RG-6. Yes,
RG-6 is 75 ohms, but for a 50 foot run the loss from the mismatched impedence
of the low loss RG-6 would be less than a high loss matched coax such as
RG-58. RG-6 is about 26 cents a foot at Rat Shack.
73's,
Robert Harris, KF4OEG
skw...@ix.netcom.com
http://kf4oeg.gt.ed.net - server currently down, try in a few days
Curt Phillips wrote:
> I have a situation where I cannot use a large diameter coax cable for a 2
> meter radio and a scanner.
>
> There will be about a 50' run from the scanner to the antenna and about a
> 50' run from the 2 meter radio to the antenna.
>
> Since the larger diameter 9913 type cables can't be used, which is the best
> choice among the small diameter cables?
>
> It doesn't have have to be the same cable for both applications. I seem to
> remember reading about some small diameter 75 ohm cable
> (maybe from a cable TV application) that does a reasonably good job in
> scanner applications. Perhaps that would be the best choice for the
> scanner.
>
Andy Moss
Robert Harris wrote:
>
> For a scanner application with small diameter coax, I would use RG-6. Yes,
> RG-6 is 75 ohms, but for a 50 foot run the loss from the mismatched impedence
> of the low loss RG-6 would be less than a high loss matched coax such as
> RG-58. RG-6 is about 26 cents a foot at Rat Shack.
I disagree.
75 Ohm coax isn't worth a pinch of shit. It's useless for transmitting
and completely unsaleable to another radio hobbyist should you no longer
need it.
Buy 50 Ohm coax and keep your options open.
For your application any "mini" RG8x non-contaminating coax is your best
bet.
The attention paid to impedance of "TV" cable by manufacturers is non-
existant whereas in 50 Ohm it's critical. I've seen many 75 Ohm cables
with the centre conductor offset within the foam dielectric.
--
Andy Moss
"Whose woods these are I think I know...."
Bea and Marvin Jones
In rec.radio.amateur.antenna Andy Moss <and...@ibm.net> wrote:
: Robert Harris wrote:
:>
:> For a scanner application with small diameter coax, I would use RG-6. Yes,
:> RG-6 is 75 ohms, but for a 50 foot run the loss from the mismatched impedence
:> of the low loss RG-6 would be less than a high loss matched coax such as
:> RG-58. RG-6 is about 26 cents a foot at Rat Shack.
: I disagree.
And, I disagree with your disagree. <g>
For a scanner application, with whatever for a scanner antenna, what are
the odds that the scanner will see 50 ohms looking into ANY feedline at
whatever frequency -- even if the scanner was designed for 50 ohms at
EVERY frequency?
Put the scanner at the antenna and run zip cord down to a speaker. :-)
Jonesy - W3DHJ
Andy Moss
Bea and Marvin Jones wrote:
>
> In rec.radio.amateur.antenna Andy Moss <and...@ibm.net> wrote:
> : Robert Harris wrote:
> :>
> :> For a scanner application with small diameter coax, I would use RG-6. Yes,
> :> RG-6 is 75 ohms, but for a 50 foot run the loss from the mismatched impedence
> :> of the low loss RG-6 would be less than a high loss matched coax such as
> :> RG-58. RG-6 is about 26 cents a foot at Rat Shack.
>
> : I disagree.
>
> And, I disagree with your disagree. <g>
8-)
> For a scanner application, with whatever for a scanner antenna, what are
> the odds that the scanner will see 50 ohms looking into ANY feedline at
> whatever frequency -- even if the scanner was designed for 50 ohms at
> EVERY frequency?
This is a good point. But it's usually good to start with spec. Most
receivers are optimized plugged into 50 Ohm test gear. Tuned front ends
with wide coverage are basically tweaked up at the top end. If a
mismatch were to occur, it would undoubtedly be at the bottom of the
band in question. As far as antenna themselves being 50 Ohms, I agree
that not too many fit that bill! A good discone, log-periodic or
folded-dipole are very good though.
I agree that the difference in signal will be minute between the two.
The other reasons I gave make it worth *my* while not to bother with 75
Ohm coaxial cables. YMMV.
> Put the scanner at the antenna and run zip cord down to a speaker. :-)
Believe it or not, zip cord is typically 50 Ohms and I've seen QRP Tx/Rx
stations using it successfully as feedline. Also, one notorious CBer in
town used a bastardized extension cord for his antenna. He split the
conductors with each leg about 102" and formed a dipole stapled to the
wall of his house. I can't argue it, the VSWR was good and so was his
signal!
Robert Harris
Andy Moss wrote:
> Robert Harris wrote:
> >
> > For a scanner application with small diameter coax, I would use RG-6. Yes,
> > RG-6 is 75 ohms, but for a 50 foot run the loss from the mismatched impedence
> > of the low loss RG-6 would be less than a high loss matched coax such as
> > RG-58. RG-6 is about 26 cents a foot at Rat Shack.
>
> I disagree.
>
> 75 Ohm coax isn't worth a pinch (edited). It's useless for transmitting
> and completely unsaleable to another radio hobbyist should you no longer
> need it.
>
He is using this for a scanner, he isin't going to be transmitting. Its not
unusable at all - works just great for receiving.
> Buy 50 Ohm coax and keep your options open.
>
> For your application any "mini" RG8x non-contaminating coax is your best
> bet.
>
> The attention paid to impedance of "TV" cable by manufacturers is non-
> existant whereas in 50 Ohm it's critical. I've seen many 75 Ohm cables
> with the centre conductor offset within the foam dielectric.
>
Not critical at all with receiving
> --
> Andy Moss
> "Whose woods these are I think I know...."
73's,
Roy Lewallen
In article <34BC83...@ibm.net>, and...@ibm.net wrote:
>Robert Harris wrote:
>>
>> For a scanner application with small diameter coax, I would use RG-6. Yes,
>> RG-6 is 75 ohms, but for a 50 foot run the loss from the mismatched impedence
>> of the low loss RG-6 would be less than a high loss matched coax such as
>> RG-58. RG-6 is about 26 cents a foot at Rat Shack.
>
>I disagree.
>
>and completely unsaleable to another radio hobbyist should you no longer
>need it.
>
>
>For your application any "mini" RG8x non-contaminating coax is your best
>bet.
>
>The attention paid to impedance of "TV" cable by manufacturers is non-
>existant whereas in 50 Ohm it's critical. I've seen many 75 Ohm cables
>with the centre conductor offset within the foam dielectric.
That's quite an interesting generalization about 75 ohm cable. I've used 75
ohm cable for transmitting for years, and have measured the impedance of
"50 ohm" cable at over 60 ohms. I've found good-quality cable in both
impedances, and garbage cable also in both impedances. Simply marking a
cable as 50 ohms doesn't assure its quality, and having a nominal impedance
of 75 ohms doesn't mean the quality is poor.
Roy Lewallen, W7EL
Ed G.
The amount of misinformation and misunderstanding of cable loss and
impedence on this subject's previous messages is incredible. It would be
beneficial to many of you to get a copy of the ARRL Handbook for Radio
Amateurs and perhaps a Belden catalog and study up on the subject.
Ed W7DXZ
REPLY INFO:
===========================================================
Return address modified to prevent automatic SPAM response.
TO REPLY: remove the "lillypads" from my return address.
===========================================================
Andy Moss
Roy Lewallen wrote:
>
> That's quite an interesting generalization about 75 ohm cable.
And generally true of the cheapie stuff that would be most appealing to
hobbyists.
> I've used 75
> ohm cable for transmitting for years, and have measured the impedance of
> "50 ohm" cable at over 60 ohms.
That could be true. I've got one 50 Ohm cable that measures infinity
and
another zero! 8-)
> I've found good-quality cable in both
> impedances, and garbage cable also in both impedances. Simply marking a
> cable as 50 ohms doesn't assure its quality, and having a nominal impedance
> of 75 ohms doesn't mean the quality is poor.
I was speaking in gross generalities, Roy. Through my CB years and into
ham
then into the profession, I've yet to see new 50 Ohm cable that wasn't
useable
with VHF and UHF transmitters.
I've seen plenty of shitty 75 Ohm stuff pumped out of Asian sweat-shops
that I
wouldn't use due to it being inadequate for the intended purpose.
--
Andy Moss - VE3YES
Whatever the top license class is, that's the one I have....8-)
Gary Coffman
On 14 Jan 1998 19:35:49 GMT, Bea and Marvin Jones <jo...@shell.rmi.net> wrote:
>In rec.radio.amateur.antenna Andy Moss <and...@ibm.net> wrote:
>: Robert Harris wrote:
>:>
>:> For a scanner application with small diameter coax, I would use RG-6. Yes,
>:> RG-6 is 75 ohms, but for a 50 foot run the loss from the mismatched impedence
>:> of the low loss RG-6 would be less than a high loss matched coax such as
>:> RG-58. RG-6 is about 26 cents a foot at Rat Shack.
>
>: I disagree.
>
>the odds that the scanner will see 50 ohms looking into ANY feedline at
>whatever frequency -- even if the scanner was designed for 50 ohms at
>EVERY frequency?
Realize that the scanner is the terminating load for the line in a receiving
situation. The antenna is the source. So if you use a cable that is the same
impedance as the scanner input, there will be a match, and a SWR of 1:1
on the cable, regardless of the antenna feedpoint impedance.
We're so used to thinking of the antenna as the terminating load for our
*transmissions* that we forget that this isn't true in a receiving situation.
mo...@hotmail.com
In article <34BDD9...@ibm.net>,
and...@ibm.net wrote:
> Roy Lewallen wrote:
> >
> > That's quite an interesting generalization about 75 ohm cable.
>
> And generally true of the cheapie stuff that would be most appealing to
> hobbyists.
>
> > I've used 75
> > ohm cable for transmitting for years, and have measured the impedance of
> > "50 ohm" cable at over 60 ohms.
>
> That could be true. I've got one 50 Ohm cable that measures infinity
> and
> another zero! 8-)
>
> > I've found good-quality cable in both
> > impedances, and garbage cable also in both impedances. Simply marking a
> > cable as 50 ohms doesn't assure its quality, and having a nominal impedance
> > of 75 ohms doesn't mean the quality is poor.
>
> I was speaking in gross generalities, Roy. Through my CB years and into
> ham
> then into the profession, I've yet to see new 50 Ohm cable that wasn't
> useable
> with VHF and UHF transmitters.
__________
> Whatever the top license class is, that's the one I have....8-)
I didn't realize CB was considered a profession. What *is* the top
of your license class?
Just curious.
-------------------==== Posted via Deja News ====-----------------------
http://www.dejanews.com/ Search, Read, Post to Usenet
Andy Moss
Ed G. wrote:
>
> The amount of misinformation and misunderstanding of cable loss and
> impedence on this subject's previous messages is incredible. It would be
> beneficial to many of you to get a copy of the ARRL Handbook for Radio
> Amateurs and perhaps a Belden catalog and study up on the subject.
I have no misunderstanding about cable losses, Ed. The ARRL book is an
excellent text. However, like many educational texts they don't factor
in products that don't meet the minimum requirements.
Cheers!
Fractenna
>You can try RG-8X, also called mini-8. This is a foam insulated 50 ohm
>cable about the size of RG-58. The loss is higher than RG-8, but less
>than RG-58. Radio Shack carries it.
>
>A common CATV 75 ohm cable would be RG-6. Its loss is a bit less
>than RG-58, but the mismatch may make it worse in practice. I'd stick
>with 50 ohm cables in a 50 ohm system unless there was a compelling
>reason to use a different impedance.
>
>Gary Coffman KE4ZV | You make it |mail to ke...@bellsouth.net
>534 Shannon Way | We break it |
>Lawrenceville, GA | Guaranteed |
>
expensive. Nemal sells it.
Chip N1IR
Robert Harris
Ed G. wrote:
> The amount of misinformation and misunderstanding of cable loss and
> impedence on this subject's previous messages is incredible. It would be
> beneficial to many of you to get a copy of the ARRL Handbook for Radio
> Amateurs and perhaps a Belden catalog and study up on the subject.
>
> Ed W7DXZ
I suppose this one was aimed at me. I was just simply trying to help
keeping in mind what was being looked for, and what would work with on a
receiving stand point. He wanted a small diameter coax that could be used
for receiving with a scanner. I suggested RG-6 because it is small diameter,
cheap, readily available, and even though it is 75 ohms the mismatch would be
less in a shorter run than in the same run of a 50 ohm coax with higher
loss. I didn't intend to start all this, just help.
73's,
Robert Harris, KF4OEG
skw...@ix.netcom.com
http://kf4oeg.gt.ed.net - server is down for a while, try it agian later.
Fractenna
>Subject: Re: Best small diameter coax for VHF/UHF
>From: Andy Moss <and...@ibm.net>
>Date: Wed, Jan 14, 1998 18:52 EST
>Message-id: <34BD4F...@ibm.net>
>
>Bea and Marvin Jones wrote:
>>
>> In rec.radio.amateur.antenna Andy Moss <and...@ibm.net> wrote:
>> : Robert Harris wrote:
>> :>
>> :> For a scanner application with small diameter coax, I would use RG-6.
>Yes,
>> :> RG-6 is 75 ohms, but for a 50 foot run the loss from the mismatched
>impedence
>> :> of the low loss RG-6 would be less than a high loss matched coax such as
>> :> RG-58. RG-6 is about 26 cents a foot at Rat Shack.
>>
>> : I disagree.
>>
>> And, I disagree with your disagree. <g>
>
>
>> For a scanner application, with whatever for a scanner antenna, what are
>> the odds that the scanner will see 50 ohms looking into ANY feedline at
>> whatever frequency -- even if the scanner was designed for 50 ohms at
>> EVERY frequency?
>
>receivers are optimized plugged into 50 Ohm test gear. Tuned front ends
>with wide coverage are basically tweaked up at the top end. If a
>mismatch were to occur, it would undoubtedly be at the bottom of the
>band in question. As far as antenna themselves being 50 Ohms, I agree
>that not too many fit that bill! A good discone, log-periodic or
>folded-dipole are very good though.
>
>I agree that the difference in signal will be minute between the two.
>The other reasons I gave make it worth *my* while not to bother with 75
>Ohm coaxial cables. YMMV.
>
>> Put the scanner at the antenna and run zip cord down to a speaker. :-)
>
>Believe it or not, zip cord is typically 50 Ohms and I've seen QRP Tx/Rx
>stations using it successfully as feedline. Also, one notorious CBer in
>town used a bastardized extension cord for his antenna. He split the
>conductors with each leg about 102" and formed a dipole stapled to the
>wall of his house. I can't argue it, the VSWR was good and so was his
>signal!
>
>Andy Moss
>"Whose woods these are I think I know...."
>
>
hardline. If you need some flexibility then get conformable hardline.
I am not making this up; sounds like an oxymoron but isn't. In fact, I've got a
piece in my hand right now. Belden makes it. Nemal (and others) sell it. Its
plenty flexible and actually quite pretty. It has a silverized shield (I
presume).
If you look at the return loss to a 50 ohm termination you get frequency
dependent response at UHF for the other types of coax described. Conformable
hardline is virtually flat at better than -60 dB . It's expensive but not
astronomically so. Question answered :-).
73
Chip N1IR
Ed G.
>> The amount of misinformation and misunderstanding of cable loss and
>> impedence on this subject's previous messages is incredible. It would be
>> beneficial to many of you to get a copy of the ARRL Handbook for Radio
>> Amateurs and perhaps a Belden catalog and study up on the subject.
>I have no misunderstanding about cable losses, Ed. The ARRL book is an
>excellent text. However, like many educational texts they don't factor
>in products that don't meet the minimum requirements.
That's why I suggested a good catalog too, such as the Belden catalog. It
should be free at 1-800 BELDEN1 if it hasn't changed in a few years.
Also, I wasn't aiming my comments at anyone in particular, .. just in
response to the overall sense of many of the comments I saw. As of yet, no
one has done the math, or sent the formula to show why 70 ohm coax is so much
more lossy than 50 ohm coax . I will, if I don't see it soon.
mike frye
Boy, what a mess! The Belden flex hardline mentioned will turn green and corrode in
short time if exposed to the elements. If the size of the hardline Chip is talking
about is .141dia it is essentially the same center cond and Teflon dielectric used
in RG 142B/U which can be purchased at ham swap meets rather inexpensively and will
not be harmed by the weather. If your set on an RG-6 size cable, that's the same
size as RG-8X as mentioned in the very first reply to this post. Why doesn't the
author of this post let us know what is the largest dia. he can live with and we
can dis-agree all over again.
D. Holford
I know I am going to hate myself for getting into this - but I just can't
resist!
I have a 10metre half wave dipole at 60 feet above ground.
I have a tansceiver with a built-in automatic impedance matching circuit
(Antenna Tuner).
What co-ax impedance should I be using?
I would like to get maximun signal transfer on both TX and RX.
--
Dave Holford.
Roy Lewallen
It won't make any noticeable difference.
Roy Lewallen, W7EL