• Effective immediately we will be deleting, without notice, any negative threads or posts that deal with the use of encryption and streaming of scanner audio.

    We've noticed a huge increase in rants and negative posts that revolve around agencies going to encryption due to the broadcasting of scanner audio on the internet. It's now worn out and continues to be the same recycled rants. These rants hijack the threads and derail the conversation. They no longer have a place anywhere on this forum other than in the designated threads in the Rants forum in the Tavern.

    If you violate these guidelines your post will be deleted without notice and an infraction will be issued. We are not against discussion of this issue. You just need to do it in the right place. For example:
    https://forums.radioreference.com/rants/224104-official-thread-live-audio-feeds-scanners-wait-encryption.html

Question on coax...more

Status
Not open for further replies.

DewAddict

Member
Joined
Sep 12, 2005
Messages
15
Location
SE, Michigan
I am using a 800mhz disk style antenna and it has a 75ohm coax connector on it. If I run 75ohm coax to my 800mhz scanner how will reception be? Its about a 35' run. Will I see a big loss in signal compared to 50ohm. The antenna is similar to the "Discadoo" antenna but made by another company.

Thanks,

Rob
 

LarrySC

Member
Joined
Feb 9, 2001
Messages
2,091
Location
Greenville, SC
Most scannist use 75ohm coax. Some ant's require it and some dont. The scanner, however, only knows that a wire is connected. Its not really able to know any better. ALL my ant's and coax [ RG-6 ] are connected to splitters and A-B switches as needed. Changed it all over about 25 years ago. Been a happy camper ever since. Good Luck
 
N

N_Jay

Guest
The difference in loss on a 50 ohm system using 75 ohm cable is minimal.

It does make a difference, but very rarely a difference you can tell on a receive system.

Dont believe those who say it causes lots of loss, and dont believe those who say the receiver does not care. They are the two ends of the bad information spectrum.
 

Diddley

Member
Joined
Dec 19, 2004
Messages
73
Location
Chatham, ON
Coax

I've got over 100ft of RG-6 coax running into my BCT8, and all is well. I'm using the "Scantenna" ST2 antenna hooked up to RG6 that I had connected to an old satellite. Everything works beautifully. I got some intermod in the VHF bands, but a simple $4.99 in-line attenuator from Radio Shack helped reduce this. RG-6, for most people, is plenty adequate. N Jay is correct. Personally, I always thought LMR-400 coax was overrated, and you certainly don't need to spend all kinds of $$$ to get a good, decent, reliable signal. Just stay away from all that "dollar store" junk, and you should be fine...

73's!
Diddley
 

DaveH

Member
Joined
Jul 29, 2001
Messages
3,072
Location
Ottawa, Ont.
N_Jay said:
The difference in loss on a 50 ohm system using 75 ohm cable is minimal.

It does make a difference, but very rarely a difference you can tell on a receive system.

Dont believe those who say it causes lots of loss, and dont believe those who say the receiver does not care. They are the two ends of the bad information spectrum.
I more or less agree, but would add some detail.

The overall loss depends on the coax loss plus an effect from the mismatch.
Unless this is a critical/low-loss requirement, the effect may indeed be small
but not necessarily unnoticeable. Somewhere is a website with a calculator
that takes this into account, just can't lay hands on it.

I don't know where Larry's claim that most "scannist" use 75 ohm coax is
from. I tend to stick to 50 ohms even though cheaper 75-ohm coax may be
available (like the old cable co. end-of-roll, used to throw it away; now they
probably sell it...). Nothing should stop anyone from using 75 ohm stuff if
they know what they're getting.

Dave

PS DewAddict I have an (O/T) story. I believe Mountain Dew in the U.S. contains
caffeine, whereas at the time it did not (and may still not) in Canada. A guy
came up here once, who was used to getting has caffeine fix from M.D.
rather than coffee etc. Not knowing this, he started feeling tired and run-down
as the day wore on...until the can content label was checked, uncovering the
horrible truth.... :)
 

DaveH

Member
Joined
Jul 29, 2001
Messages
3,072
Location
Ottawa, Ont.
Just found the cable loss calculator website from a different thread... :)

http://www.ocarc.ca/coax.htm

Plugging in 35' of RG-6/U, 850MHz, 1.5 VSWR gives a coax loss of around
3dB (not bad) and VSWR loss about 0.14dB (ignore it). RG-59/U is slightly
worse. This calculator assumes a mismatch on one end (not both ends) but
it gives a good indication that there isn't a problem.

Dave
 
N

N_Jay

Guest
DaveH said:
"I more or less agree,"
. . .
Plugging in 35' of RG-6/U, 850MHz, 1.5 VSWR gives a coax loss of around
3dB (not bad) and VSWR loss about 0.14dB (ignore it). RG-59/U is slightly
worse. This calculator assumes a mismatch on one end (not both ends) but
it gives a good indication that there isn't a problem.

Dave
I guess instead of agreeing "more or less", you can just agree MORE. :lol: :lol:
 

kb2vxa

Completely Banned for the Greater Good
Banned
Joined
Mar 22, 2005
Messages
6,126
Location
Point Pleasant Beach, N.J.
Hi Do The Dew or whatever are you,

Some like to complicate things, I like to simplify. Every question you ask or are going to ask has been answered countless times on these forums, all you have to do is read. Now please allow me to baffle you with my bullstuff, I can't dazzle you with my brilliance.

"I am using a 800mhz disk style antenna and it has a 75ohm coax connector on it."

There is no such thing as a 75 ohm connector.

"If I run 75ohm coax to my 800mhz scanner how will reception be?"

I haven't a clue.

"Its about a 35' run."

Not far so it shouldn't be tired at the finish.

"Will I see a big loss in signal compared to 50ohm."

About 25 ohms worth.

"The antenna is similar to the "Discadoo" antenna but made by another company."

The name on the label is irrelevant, yours is Rob, mine is Warren, we are both men (or I hope you are).

OK, now my ascerbic wit is out of the way. For that short a run any cable besides RG-58 or 59 will do nicely. Considering loss as we all do RG-58 is the cable of choice for mobile installations because it's thin and easy to work with and it's only about 10' long, otherwise it's for HF only. For runs of about 50' or so most common cables like RG-8AU polyfoam are just fine and for about 100' you start thinking Belden 9913 or Times Microwave LMR series. More than that and it's semi-rigid air dielectric or hard line, the longer the run the more loss, the "better" the cable the less loss, things tend to balance out.

OK, now that I've totally confused you (I love to compete in that department) go do your homework. Download a coax chart (manufacturer's specs) and you'll see more accurately than we can describe in words exactly how cable length vs. frequency affects signal loss. Then research connectors and adapters, you'll see they have no particular characteristic impedance nor do they have any measurable signal loss. Thus armed you're prepared to do battle against the misinformation so common on this Battlefield Earth.

Pardon me, I also like to steal titles, this one from L. Ron Hubbard. If you think Dienetics stinks on ice you haven't read his childish science fiction, even John Travolta couldn't save the movie. (;->)

Oh, almost forgot!
"Those websites are great tools."
You've only begun to scratch the surface, wait until you start reading some comprehensive study material on RF theory. Then your name will be up there in lights just like mine and Jerry Lewis (The Nutty Professor) but I don't have buck teeth.
 
N

N_Jay

Guest
kb2vxa said:
Hi Do The Dew or whatever are you,

Some like to complicate things, I like to simplify. Every question you ask or are going to ask has been answered countless times on these forums, all you have to do is read. Now please allow me to baffle you with my bullstuff, I can't dazzle you with my brilliance.

"I am using a 800mhz disk style antenna and it has a 75ohm coax connector on it."

There is no such thing as a 75 ohm connector.

. . . .. ..
Just to piss you off!:twisted: :lol: :twisted:


Yes connectors have characteristic impedance.

You usually don't see it with consumer crap, but properly designed systems use matched connectors.

The most common connector with a specified impedance is the BNC which has a different size center pin.

http://www.coaxicom.com/pdfs/bnc.pdf

Read the warning about mating different impedance "N" connectors.
http://www.coaxicom.com/pdfs/type-n.pdf
 
Last edited:

DaveH

Member
Joined
Jul 29, 2001
Messages
3,072
Location
Ottawa, Ont.
kb2vxa said:
There is no such thing as a 75 ohm connector.
I recall Andrew Antenna offered 50 and 75-ohm (pardon me, 52- and 73-ohm)
versions of the venerable PL-259, which are called "UHF" connectors. I think the
old PL-259 (Amphenol 83-1SP) was originally designed for IBM data terminals
that used RG-62/U coax (93 ohms). One wonders why the Chicken Banders
didn't go for 93-ohm antennas and 93-ohm radios to "keep their SWR down".

GBGL

Dave
 
N

N_Jay

Guest
DaveH said:
I recall Andrew Antenna offered 50 and 75-ohm (pardon me, 52- and 73-ohm)
versions of the venerable PL-259, which are called "UHF" connectors. I think the
old PL-259 (Amphenol 83-1SP) was originally designed for IBM data terminals
that used RG-62/U coax (93 ohms). One wonders why the Chicken Banders
didn't go for 93-ohm antennas and 93-ohm radios to "keep their SWR down".

GBGL

Dave
I think it was designed for military UHF systems like early radar.

I think it was designed for 50/52 ohms.
 

dalonzi

Member
Joined
Jan 22, 2007
Messages
7
Location
Massachusetts
Hi. I am trying to decide on the scanntennaT2 as a purchase. My question is can i use Thomas and Betts compression connectors on the RG6 quad shield that I plan on using? The same cable and connectors that are on my satellite dishes. Instead of the crimp on F connectors.

thanks for your help
 

jyams

Member
Joined
Oct 31, 2005
Messages
34
Location
Memphis, TN
Yes you can. I use several RG6 cables with compression connectors and they work just as well as the traditional "F" connectors.
 
Status
Not open for further replies.
Top