FORUM CLASSIFIEDS DIFFLOCK.com Links & Networks
Forum Homepage
Log in
Profile
Search
Private Messages
Forum Members
Register
Classified Ads
Search Ads
Place New Ad
My ads
Place your classified
ads here for FREE
NB: Adverts placed in the general
forum areas will be deleted
Difflock Homepage
Online Shop
Contact Us
FAQ
Calendar
Garage
Facebook
Twitter
Youtube
Advertise With Us - Reach your target market by advertising on the Difflock.com forum.
Click here or call 0845 125 9407


Coax ?

 
 
Post new topic   Reply to topic    Difflock Forum Index -> Electrical, Comms and ICE
View previous topic :: View next topic  
Author Message
andypandysdirtylandy
Gate Opener


Joined: 23 Feb 2007
Odometer: 44




PostPosted: Sat May 02, 2009 2:55 pm    Post subject: Coax ? Reply with quote

Can anyone tell me if RG 59 B/U is ok to use on a cb set up ?
Back to top
View user's profile Send private message Visit poster's website
Kitesurf
Difflock Royalty


Joined: 28 Feb 2005
Odometer: 14197
Location: Luton, Beds


1994 Toyota Surf

PostPosted: Sat May 02, 2009 3:58 pm    Post subject: Reply with quote

It is no good for CB. It is 75 Ohm. You need RG58 which is 50 Ohm.

There is a cheat that can be done to transform from 75 to 50 Ohm but you would need to be able to calculate an electrical 1/4 wavelength of cable, which may end up too short on a vehicle installation. Multiples of a 1/4 wavelength would work but would leave you with extra cable coiled up in the vehicle. It is far easier to use the right stuff.

__________________________________
Motorist who drove his 4x4 up Snowdon sentenced to appear on Top Gear.
Back to top
View user's profile Send private message
northumberlad
Guest








PostPosted: Sat May 02, 2009 4:04 pm    Post subject: Reply with quote

RG-58/U is what you want.
Back to top
andypandysdirtylandy
Gate Opener


Joined: 23 Feb 2007
Odometer: 44




PostPosted: Sat May 02, 2009 4:54 pm    Post subject: Reply with quote

I'm co phasing two whips and I've been told I need 75 ohms coax and I had this stuff knocking about but I think its for video rather than audio thus the question Question
Back to top
View user's profile Send private message Visit poster's website
northumberlad
Guest








PostPosted: Sat May 02, 2009 6:10 pm    Post subject: Reply with quote

have heard of people using 50ohm & 75ohm for phased arraysif you use 75ohm, only use it for the co-phase harmes (the theory for using 75 ohm cable seema to be that the two antemas in paralel present a 70ohmish load) the feeder back to the radio should still be 50ohm
Back to top
mrcheese
Mud Obsessed


Joined: 14 Oct 2003
Odometer: 6339




PostPosted: Wed May 06, 2009 8:55 am    Post subject: Reply with quote

This link may be of interest.

http://www.bellscb.com/cb_radio_hobby/antennas/antarray.html

Not sure if you will be able the two antennas far enough apart for it to work on vehicle. I am sure that I have read about spacing closer than 1/4 wavelength, but that will change the feed impeadance to an even lower value
Back to top
View user's profile Send private message
northumberlad
Guest








PostPosted: Wed May 06, 2009 9:41 am    Post subject: Reply with quote

the 'use 18" (1 wavelength-ish) of cable' always makes me a bit wary of advice because it't a cheat to get the VSWR down by making relections coincident with the outgoing signal, you still have reflections from impeadance mis-matches they are just hiding. the rest of it seems to make sense from what i can remember fro collage It's just the trying to cheat the VSWR that annoys me
Back to top
mrcheese
Mud Obsessed


Joined: 14 Oct 2003
Odometer: 6339




PostPosted: Thu May 07, 2009 1:05 pm    Post subject: Reply with quote

It is not a cheat if done properly. The first assumption is that the antenna is of the correct lenght otherwise the the feed point impedances are not what you are expecting. Think of it as impeadance transformation. The remaining 50ohm cable back to the radio is then correctly matched.

What is more of a cheat is an antennna matiching unit at the radio end. This allows the radio to see the correct 50 ohms. That means the coax could actually be have a very high VSWR and therefore be lossy.
Back to top
View user's profile Send private message
.
Difflock Royalty


Joined: 19 Jun 2002
Odometer: 40007
Location: Northern Ireland's Gold Coast


2009 Land Rover 110 CSW

PostPosted: Thu May 07, 2009 1:44 pm    Post subject: Reply with quote

mrcheese wrote:
This link may be of interest.

http://www.bellscb.com/cb_radio_hobby/antennas/antarray.html

Not sure if you will be able the two antennas far enough apart for it to work on vehicle. I am sure that I have read about spacing closer than 1/4 wavelength, but that will change the feed impeadance to an even lower value


Quote:
So the final question is : "why do I want to do this?"


Personally I don't see the point!

__________________________________
Bert the Defender 110 XS - because it's Cool (work it out yourself!)
Lolita the Lightweight
???? the V8 90 CSW
Suzuki DL1000 V-Strom - yes that's right, I have a Zook!
Back to top
View user's profile Send private message Visit poster's website eBay Name
nivapilot
Guest








PostPosted: Thu May 07, 2009 6:07 pm    Post subject: Reply with quote

. wrote:
mrcheese wrote:
This link may be of interest.

http://www.bellscb.com/cb_radio_hobby/antennas/antarray.html

Not sure if you will be able the two antennas far enough apart for it to work on vehicle. I am sure that I have read about spacing closer than 1/4 wavelength, but that will change the feed impeadance to an even lower value


Quote:
So the final question is : "why do I want to do this?"


Personally I don't see the point!


Isn't this what the american truckers do?
Fit two antenna on the outer mirror stays, to get the signal to go front and rear further, so that they don't get too much from either side.
Back to top
Kitesurf
Difflock Royalty


Joined: 28 Feb 2005
Odometer: 14197
Location: Luton, Beds


1994 Toyota Surf

PostPosted: Thu May 07, 2009 11:34 pm    Post subject: Reply with quote

I understand what you want to do now, which is to make a co-phasing harness. I too don't really see the point, unless it is for a vehicle where you are going to be doing a lot of motorway driving.
Another problem is that you have to take the velocity factor of the coax into account, so an electrical 1/4 Wave will be, 75/fMHz x VF = Electrical Length, which is 75/27.405 x 0.66 = 1.8M. The lead out from your CB can be a random length of 50 Ohm coax going to a T-Piece with a length, as above, going to each antenna. The best way to set it up would be to set the SWR for each antenna, while it is being fed with a single 50 Ohm coax, then add your T-Piece and connect your 75 Ohm phasing lines to the antennas. For a maximum of 3dB gain, which represents just one S Point, it is a lot of work. As has been pointed out above, antenna spacing is also going to have an effect on the impedence presented to the transmitter.

I have done it for the lower frequency ham bands (80 and 40M) where it is more of an asset for RX rather than TX, although one S Point can make all the difference, when trying to work New Zealand on those bands! Very Happy

__________________________________
Motorist who drove his 4x4 up Snowdon sentenced to appear on Top Gear.
Back to top
View user's profile Send private message
mrcheese
Mud Obsessed


Joined: 14 Oct 2003
Odometer: 6339




PostPosted: Fri May 08, 2009 10:02 am    Post subject: Reply with quote

Phased array verticals are great fun on the lower HF bands. But a four element system uses an awful lot of coax. Shocked

As Phil says, probably more effective on receive as they can be used to null out noise.
Back to top
View user's profile Send private message
Display posts from previous:   
Post new topic   Reply to topic    Difflock Forum Index -> Electrical, Comms and ICE All times are GMT - 12 Hours
Page 1 of 1

 
Jump to:  
You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum
You cannot vote in polls in this forum
You cannot post calendar events in this forum
Adrian Flux 2023

Service Kits

Oil Safe

Facebook

Evo Oils

Join our mailing list for upcoming events, special offers, discount coupons and expert advice on the latest 4x4 products!

* indicates required





    
Powered by phpBB © phpBB Group