coax cable

[Jerry]

looking at remounting my PRS antenna and reinstalling another on a different band, been looking at coax cable, Dick Smith seem to sell all the connectors and crimp tools etc, seems to be RG-58 and RG-59, is TV grade? RG-59 at $0.40c/m ok to use or is it better to get the more expensive RG-58 ($1.44/m) 100m roll is $80.

Is there any better place in Welly to get this stuff ie cheaper and the crimp or screw connectors?

[Sadam_Husain]

I'm not an aeril guru but for the short length of cable you need its not really going to make much of a $$$$ difference which one you buy and whether you get a discount or not?

But I think those cables could be different resistances (dont ask me what resistences they are) and you'll need the right one to make your radio go properly and I think you have to cut the cable the right length to match the wave length or something like that.... somebody more clever than me will know

disclaimer: I'm not a guru on this shit and someone might steer you in the right direction


Edit*
I have got a coax crimp tool somewhere if you want to borrow it Jerry

[taz01]

you tightwad for 18 to 50 bucks buys you all you need pre tuned.............

http://www.dse.co.nz/cgi-bin/dse.filere ... CTG0000305

[Jerry]

the 3 premade dse ones I have had on this truck so far in the front have all been killed in the bush, and the 3.8m is not long enough not to mention the huge RL-259 plug on the end of it, its going on the spare tyre mount this time then in the back door with a very small sealed hole then out again and then into the wing via the other door wiring (maybe an ezi release joiner for easy servicing) then thru the back interior panel (found some good plastic protection pipe for this) then across the front seat gaps (bearing in mind the front carpet is coming out)....then up to the dash to the radio

[taz01]

never the easy way with you is it jerry

[sig]

ive got crimpers jerry.RG 58 is the right cable to use .try telesound in petone (north end of nelson st) they have a good range of tv stuff and crimps etc.

[rowinz]

I just mounted my PRS last week. I was surprised at the quality of the coax supplied with the aerial. I have used heaps of TV coax over the over (for TV) and the exterior winding is really crap compared to the aerial stuff. I'd say got the flash stuff, especially if you are putting longer than usual cable length in.

disclaimer...I am no expert either...

[Jerry]

If I didn't keep hitting trees then I would'nt have this problem

[3VILC]

The cheap tv stuff usually only has a cr*p fine copper braid for the shield, the more expensive satellite grade or aerial cable usually has a nickle braid as well as a foil layer which would be far better in an automotive environment to prevent interference. As previously mentioned the impedance is probably also different, tv coax is 75ohm, cant remember off the top of my head what you need for cb. And yes the length of the cable is generally quite specific and should divide into the wavelength. From memory AM cb is generally 3.6meters which is i think 1/3rd wavelengh. 3.8m on a UHF is likely full wavelength so youd probably want to go to 7.2m.
Again its been a long day at work and the numbers are probably not accurate and probably not useful but do some research or you'll likely get poor signal or not much range.
Measure twice cut once as the old saying goes

[dazza85]

... ts going on the spare tyre ...(maybe an ezi release joiner for easy servicing) ....

If at all possible avoid joins / joiners they suck up power ...



disclaimer: I'm not a guru either.

Otherwise I would be able to tell you what the cable length has to be multiples of ...

Edited to insert the info

http://www.mobileone.com.au/antennas/tune.htm

Download this page as a PDF file How To Tune.pdf (right click then save)

Tuning Mobile One Antennas

Only Mobile One, gives the after sales support you need! so why buy any other brand?
Although each Mobile One Antenna is made to frequency at the factory, we, nor anyone else, can simulate
all installation possibilities. Therefore most antennas unless stated otherwise may need slight adjustments.
The addition of springs or adaptors may make your antenna electrically longer so tuning may become
necessary. Take all SWR measurements with the antenna in it's final mounting position include all accessories
then adjust if necessary.

Mobile One UHF Antenna Range
(S474, S474B, M474, RF470, FDW470, BNCHW, COL6M, ETC)
All Mobile One UHF Antennas do not need to be tuned they are extremely broad band and will have a SWR
below 1.5 to 1 if they are installed correctly.

Mobile One Pretuned Antenna Range
(DX125CD, DX140CD, DX148CD, DX160CD, DX170CD)
These antennas have been made with 1/4" constant diameter fibreglass rods that are identical in diameter,
and have been wound using a computer operated winding machine that ensures each one has been made
identically to the previous one. The helical wind in these antennas is designed to be as broad band as
possible, the end result is these antennas will work with a SWR below 1.5 to 1 on almost any position on
the vehicle as long as they have been installed properly with sufficient ground plane area.


The Base, Connector & Cable Assembly
The Base should always be suitable for the frequency it is to operate on, for example, with the frequency
range 0~100MHz any good base is suitable (Base A, Base UL,Base BSS, Dipole Base,Sam Base, etc)
However the frequency range of 100~1200MHz is sensitive to loss so it's very important that you use
a base that is suitable such as (Base UL, Dipole Base etc) If in doubt shout

The Cable should always be a multiple of 1/2 wave length of the frequency ie: for 27MHz the length
should be either 3.6m, 7.2m, 10.8m or 14.4m etc. In the case of UHF CB it is not important as the
vast majority of UHF antennas are broad band and do not need to be tuned.

The Connector is usually a PL259 or a BNC. In either case it is important that you ensure that there is
proper connectivity and no shorts in the connector. PL259's are known to give problems if the coax is loose
in the barrel. With BNC connectors it is common that the pin in the centre has fallen in and is not making
a proper contact. BNC's are known for their short circuits as they can be more difficult to assemble.

If possible you should check your SWR after installation.

The Installation
When installing any Base & Lead Assembly it is important that the Base is properly earthed to the vehicle.
The earth is the braid or the outer part of the coax and is connected to the base plate of the base.
This base plate is usually the part that earths to the underside of the vehicle body. It is important that
there is no short circuit between the base plate and the base bolt that the antenna is connected to.
It is a good idea that if you are installing a Base & Lead Assembly through the inside of a vehicles motor
you keep the cable as far away from the electrical system such as ignition coils as possible as this will help
to reduce noise. After installing the Base & Lead Assembly, using a multimeter check for continuity between
the collar of the connector and any metal part of the vehicle, also check for short circuit on the collar end.
If you have excess coax and have no other choice but to coil it then try to run it up and down some way.
If you coil coax you may create inductance and this may lead to problems.

The SWR Meter
It is important that the SWR Meter should be of good quality and cover the frequency that you wish to test
and that the lead that goes from the SWR meter to the Transceiver be as short as possible.

The SWR Readings
INITIAL TEST
It is of the utmost importance that the antenna have a tip on it during all SWR measurements.
Tests made without antenna tip in place will produce false information. Your goal is to achieve the lowest
REF SWR reading possible but NOTE SWR readings lower than 1.5 to 1 are quite acceptable, if your antenna
is within that range it is not necessary to tune it. After installing the SWR meter the first thing to do is
measure the SWR reading on channel on then measure the SWR reading on channel 40, if the SWR is better
on Ch 1 than on Ch 40 then the antenna is too long and will need to be tuned, however if the SWR is better
on Ch 40 than on Ch 1 the antenna is to short and cannot easily be adjusted any better. see below.

DIFFERENT ANTENNAS DIFFERENT READINGS
At this point, depending on the type and most important the length of the antenna, you will see different
results. The longer the antenna the more broad band the antenna is, ie: In the case of 27MHz CB if the antenna
is more than 40" long, the antenna's SWR after tuning should fall between Ch 1 ~ Ch 40 under 1.5 to 1.
However the shorter the antenna the more narrow band it is, ie: In the case for 27MHz CB antennas that
are shorter than 40" long the antenna's SWR after tuning will not cover all the 40 channels below 1.5 to 1 SWR.
For example, a short CB antenna such as a Rubber Ducky will only have a SWR reading of better than 1.5 to 1
on a few channels, so it may be necessary in this case to decide which particular channels you wish to
operate on. So, the shorter the antenna, the more quickly it reacts to adjustments. Extreme care should be
taken when tuning antennas less than 25" long as even a cut of 1/8" may make a big difference.

THE READINGS IN A NUTSHELL
If SWR readings are 1.5 to 1 or below on all frequencies throughout the frequency spectrum of your transceiver,
then no adjustments are required. (Dont fix it it aint broke) If the SWR FAVOURS the lowest frequency and
SWR on the highest frequency of your transceiver is above 1.5 to 1, then your antenna appears LONG on
your system, and may be CUT TO TUNE If SWR FAVOURS the highest frequency on your transceiver and the
SWR readings on the lowest frequency are above 1.5 to 1, then your antenna cannot easily be adjusted.
See below
If the SWR is worse than 3 to 1 then check for open circuit or short circuit in coax. Small antennas work
best on small ground plane areas eg: Rubber Ducky's work best on gutter mounts and 1.5mtr antennas work
best in the center of the roof of the Vehicle. Most importantly, always test antennas away from any metal
obstacles such as garage doors, fences or metal tanks. A good distance to use is 10mtrs.

Tuning The Antenna
Set your transceiver to the lowest operating frequency or Channel 1. Remove TIP from top of the antenna remembering that the TIP makes a difference as it lowers the frequency slightly, so remember to replace the
tip when measuring SWR. Using a razor blade, knife or side cutter, carefully cut 1/4" off the top, then replace
tip, then measure SWR reading on Ch 1 and Ch 40, The SWR will improve on Ch1 quicker than on Ch 40.
Continue to cut the antenna. As the antenna lowers in SWR you need to achieve a SWR of better than
1.5 to 1 on Ch 1 to Ch 40 with the best reading on Ch 20.CAUTION: As SWR reaches it's lowest point,
cut only small amounts of wire off antennas to avoid over trimming. Once you have tuned the antenna it is
a good idea to glue the tip on to prevent water, moisture or loosing the Tip
(Note that spare tips are available on request)

When checking SWR, do so in an open area.
SWR readings that are inside a building or near other objects or antennas can cause reflection
which may give a false reading. A good distance should be 1/2 wavelength (27MHz = 5 metres).


If you encounter problems see "Problems" or "Antenna Too Short" below
or contact Rochelle at Mobile One during working hours on 02-46556677 sales@mobileone.com.au

Some problems to look out for

1. Broken, shorted, pinched or kinked coax.
2. Low grade coax cable, there is a lot of it about.
3. Poor ground connections or shorted mounts.
4. Improper coax. All CB systems use 50 ohm coax. (RG58,RG213).
5. Excess coax, do not coil, run as direct as possible.
6. Insufficient ground plane area under the antenna.
7. Antenna tip not in place.

Side mounts installed too far below the top edge of the vehicle, a minimum of 2/3 the length
of the antenna should be above the roof line. Portions of the antenna which are below roof line
and close to metal will absorb reflected signals that bounce off of the vehicle this will make it
hard to tune the antenna and the performance will suffer.
Antenna Too Short?

FOR 27MHz CB Antennas More Than 40" long

Replace tip with a longer one will lower the frequency but only very slightly.

Cut heatshrink off the top and solder wire to top and rewind, then re-heatshrink
NOTE heatshrink is available from some Dick Smith Electronic stores or from Mobile One.

Call Peter at Mobile One for help on 02-46556677 tech@mobileone.com.au




FOR 27MHz CB Antennas Less Than 40" long

Replace tip with a longer one will lower the frequency.

A spring or a quick release mount will lower the frequency.

You may need to add some wire on the top of the antenna so
cut 20mm heatshrink off the top release wire then solder some wire to the end, wind
a loose wound coil on top then re-heatshrink, note heatshrink is available from some
Dick Smith Electronic stores or from Mobile One.

Call Peter at Mobile One for help on 02-46556677 sales@mobileone.com.au.

All Mobile One Antennas are covered with the Mobile One
No Worries 5 Year Warranty
Copyright © 2005 by Pride Industries.

[Sadam_Husain]

disclaimer: I'm not a guru either.

Otherwise I would be able to tell you what the cable length has to be multiples of ...

If I put my clever hat on I'd say the cable lenght would be in multiples of whatever lengths DSE sell their cables at

[Ryan]

i was having trouble with my onbord prs until i put tv grade cable in it?? now its great!!!
my 2cents

[3VILC]

there ya go.. cb antennas use 50ohm coax.. which is satellite grade, or if your a geek from way back like me lol, the old computer network coax is also a high quality 50ohm coax that many places have length upto length of laying around

[UBZ]

Have a look in Jaycar as well , might be a bit better priced than dickies.
Defiantly go crimps if possible as they are a far better termination than a screw

There are two important things to remember when crimping.
1/ Make sure the shield does not touch the center core ,but goes a far up the cable as possible.
2/ Make sure you crimp the pin the to cable core.

Those two things have caused me alot of grief in the past.

I know AM CB runs on 50ohm RG-58 , but is this the same for VHF
I know that UHF and VHF TV networks run on 75ohm RG-6 , is this the same for PRS radio

(edit :spelling)

[Jerry]

Cool thanks, had a look at DSE today, RG58 came down to $1.15 or something with my trade card , some of the crimps they were out of and they are calling me tomorrow hopefully when they are back in stock, will do another measureup annd stuff....

[tallsam66]

When i used to install thin-net computer cabling this is what i did.
After installing the cable strip both ends off & meter to make sure there wasnt a short circuit then put a plug on only 1 end of the cable...then meter again to make sure there was no short circuit..if there was it meant it was in the plug you had just terminated....if you crimp on both plugs & there is a short....you dont know which of your crimps is faulty.

[rowinz]

reading these posts I am thinking I am a big egg for cutting my coax cable supplied with aerial from 4.5m to about 1m to save coiling it up (I have experienced problems with TV cable coiled up)...
but mobileone website FAQ

"What is the truth about coax cable lengths ?
The coax cable should be as short as possible and if In situations where the antenna is already tuned i.e.: UHF
and pre-tuned 27Mhz antennas, the length is not important but still should be as short as possible."

Phew..haven't cocked it up...

[Jerry]

Ideally I would like a couple of joiners in it so its servicable if needed ie one in the back door and or another in the body, how much of a difference would this make expecially if its well insulated with a roll or 2 of tape, or even one join in the body??

[UBZ]

Ideally I would like a couple of joiners

Every join in a cable will cause signal loss and create interference.
the general rule is, the few joins/terminations the better.

You should also avoid looping cable in rolls as this acts as a Faraday loop. It works like an interference antenna.
Your much better off to bundle the excess cable in a non-uniform way.

[callum007]

just for the record... Never use satelitte cable rg6 or rg59 for your cb or prs aerials.. it has the wrong impedence 75 ohm not 50ohn. 75ohm is ok for recieve only ie am/fm aerial on your veicles. if you want less signal loss, go with RG 58 AU instead of RG58CU, its double screened from memory, or go with RG 213..

just my 2 cents. only cos i work in mobile communications all day...

If you buy a premade aerial kit, try find a GME one. or call 03 4776655 and tell them what you need.

[UBZ]

just for the record... Never use satelitte cable rg6 or rg59 for your cb or prs aerials.. it has the wrong impedence 75 ohm not 50ohn.

Cool wasn't sure weather PRS/VHF was 50ohm, know i Know