Cb swr

[Run to the hills]

Having trouble getting the swr set in the fresh tractor. Think the likely cause is that ive got the antenna mounted low down for going in low sheds, but it sets up fine with a 5ft firestick antenna. Wondered if fitting a shorter firestick could work just as well or would it lead to the same issues as the short springers.
Thanks

 

[Tarw Coch]

Good earth allways used to be key, need earth through to bare metal not through paint and to something well connected to chassis. Things like those clamp on mirror mounts were never the best because they don’t give a good earth.
Where have you got the aerial mounted?

 

[Kiwi Pete]

As above, it is quite likely the SWR is just due to being mounted close to the bodywork - it's transmitting but receiving what it's transmitting, aka reading reflected power.

And, it's also likely that the bodywork is detuning the antenna (altering its resonant frequency) if that's the case - double whammy

 

[JD6920s]

Having trouble getting the swr set in the fresh tractor. Think the likely cause is that ive got the antenna mounted low down for going in low sheds, but it sets up fine with a 5ft firestick antenna. Wondered if fitting a shorter firestick could work just as well or would it lead to the same issues as the short springers.
Thanks

Get it high, get it central, get a good earth, and get a new shed,,, or park outside the old one!

 

[Run to the hills]

Good earth allways used to be key, need earth through to bare metal not through paint and to something well connected to chassis. Things like those clamp on mirror mounts were never the best because they don’t give a good earth.
Where have you got the aerial mounted?

Yep have checked the earth with a multimeter so should be ok, its mounted onto the cab frame but maybe just too low.

 

[Run to the hills]

As above, it is quite likely the SWR is just due to being mounted close to the bodywork - it's transmitting but receiving what it's transmitting, aka reading reflected power.

And, it's also likely that the bodywork is detuning the antenna (altering its resonant frequency) if that's the case - double whammy

Aye that is what i feared, wonder if a short continuously wound antenna with a tunable tip would sort it, or maybe it was just the height of the tall firestick that made it easy to tune.

 

[snipe]

How does a mag mount earth with the rubber cover on the magnet?

 

[Henarar]

Have you got the correct length of coax cable ?
trouble is I can't remember what it is for 27 81 but swr will vary along the coax cable, I have a clip on meter that proves it
if I get chance I will see if I can find some old lengths amongst my great heap of CB stuff and measure it

Do they still use use 27 81 or is it all cept now ?

 

[Kiwi Pete]

Aye that is what i feared, wonder if a short continuously wound antenna with a tunable tip would sort it, or maybe it was just the height of the tall firestick that made it easy to tune.

In theory, yes. In practice, you often just have to try things... distances and angles usually reduce the coupling to an earth, if they are parallel then it's practically part of your antenna system.

 

[Tarw Coch]

How does a mag mount earth with the rubber cover on the magnet?

Not very well.
CB will work but not over long distances.
The better the set up the longer the range

 

[KB6930]

Not very well.
CB will work but not over long distances.
The better the set up the longer the range

All mag mounts here just chucked in nowt fancy wired to the back of the tractor radio mag mount with long springer aerials and the best one on a 6430 will do 15 miles no bother . Same set up on the fastrac might do 1 mile if it's lucky

 

[davidroberts30]

Talking of cb
Last week In Pembrokeshire there was skip from Scotland Denmark and Germany bouncing in

 

[JMM]

Not very well.
CB will work but not over long distances.
The better the set up the longer the range

Technically its not an earth you need - its a ground plane, mag mounts achieve one in a capacitive coupling between the magnet and the metal it's stuck to in the same way that wireless charging works, a large triple mag setup will give good results on cb frequencies. The biggest problem with modern kit is that it is everything is isolated, with GRP panels etc instead of the metal panels of old. Personally I would have thought a 6ft springer on a mag mount onto the weight block would have sorted the OPs problem, it may be a little directional, but you have to make some trade offs.

 

[snipe]

We have a metal sun roof with a mag mount but that is fastened to a plastic cab. So I have put a wire (1 mm thick) from sun roof to tractor chassis. should that help

 

[JMM]

We have a metal sun roof with a mag mount but that is fastened to a plastic cab. So I have put a wire (1 mm thick) from sun roof to tractor chassis. should that help

If you look around the American forums they seem to reccomend using 8 AWG wire which is about 3.25 mm, but anything is better than nothing. We always found the sunroofs on the IH XL cabs made a good enough ground plane. I started with my homebase setup in the early 80s with an Amstrad 900 with a half breed mobile whip mag mounted to an old Rover biscuit tin.

 

[Run to the hills]

In theory, yes. In practice, you often just have to try things... distances and angles usually reduce the coupling to an earth, if they are parallel then it's practically part of your antenna system.

Might have to give in and put it on the mirror with an earth strap to the cab

 

[Speedstar]

We have a few K40 mag mounts & they work very well, even on a plastic roof , glue a round bit of steel to it for them to sit on & make sure your CB is wired direct to the battery

 

[Massey Ferguson 6480]

Got mine mounted of the rear work light bracket, the tips just and so above the cab, swr 1.3. Works aswell as the springer that was on the mirror but doesnt hit doorways and trees. Had skip coming through here last week aswell.

 

[Kiwi Pete]

Might have to give in and put it on the mirror with an earth strap to the cab

You could always point the whip downwards instead of up, from the mirror

I had the whip for my side by side mounted from the plastic roof but pointing downwards towards the tray - meant I could still shoot myself under a wire or bungee-gate and it had a bit of room between the whip and rollcage - I made up a ¼wave "counterpoise" instead of a ground, just a length of coax braid trimmed to adjust SWR and then heatshrinked back along the coax - kinda turning it into a centre-fed ½wave. It went well

 

[Timbo]

You could always point the whip downwards instead of up, from the mirror

I had the whip for my side by side mounted from the plastic roof but pointing downwards towards the tray - meant I could still shoot myself under a wire or bungee-gate and it had a bit of room between the whip and rollcage - I made up a ¼wave "counterpoise" instead of a ground, just a length of coax braid trimmed to adjust SWR and then heatshrinked back along the coax - kinda turning it into a centre-fed ½wave. It went well

Is he speaking another language or???