CB SWR being a bugger

[biosurf]

After drilling the roof for the antenna last weekend, finally got around to connecting the power leads etc. for the rig but I'm having an issue with SWR so thought some of the radio Gurunerds might have an idea or two.


Just been out to the car and thought I would check the SWR with a cheapie hand held I have (Eurosonic Ultimate) as if there was anything massively amiss I thought I would mind blowing that less I bought an adapter to allow me to connect the coax to the handhelds bayonet fitting so can't see a reason not to check SWR that way

Connected up the SWR meter on FWD, pressed PTT and adjusted the Cal knob until the meter was at 'SET'. When I turned to REF the needle stayed where it was

I still have my old magmount attached to the bonnet So I connected the handheld and SWR meter to that and couldn't get the meter up to SET. The needle was about half way across the red but I ran out of dial before it would go to SET. With it in this position (half way across the red) I switched to REF if dropped all the back to the left (off the scale)


Any thoughts?

Its a roof mounted antenna with the 'star' connector on the back. I didnt wire brush the inside of the roof as it was tricky to access.

Its a brand new out of the box antenna. I did have to coil the whip around my girlfriends (enormous!) suitcase to bring it home but its still straight.

I didnt have to cut the coax at all the 17 feet of it happened to be precisely right to reach from the roof around the inside of the trim, under the carpet and up to the dash. (In fact it was so close it was getting scary)


The SWR meter and cable are second hand. Could it be that they are no good or would it just read nothing if it was knackered?

Or shouldn't I be checking SWR with a handheld?

Grrr... and indeed, Feck!

[g0pey]

Hi

What antenna are you using and what frequency/channel did you do the SWR measurement at ?

From my experience , all radios profess to be 50ohms but in reality some "tweaking" of the antenna will be required. Best to set the antenna up for the radio you are actually going to use.

Also, in the past I have had some real bother with those bnc to pl259 adapters , admittedly, not at 27Mhz.

SWR meters .. you get what you pay for.. also with the added disadvantage that you are matching the antenna to radio via another set of (possibly) complex impedances ( the swr meter ), but it should be close enough.


Regards

Bob

[biosurf]

Hi Bob

Thanks for your response

The antenna is a Wilson 5000

I did the test on channel 20

Completely agree re: SWR'ing with the rig to be used and was going to switch to this once I knew that it was in the right ball park

Any thoughts on decent sub £30 SWR meters?

[g0pey]

HI

Is that antenna supposed to be pre matched ? if so which band i.e uk or europe ?

which channel 20 europe or uk ?

Did you tweak the antanna ( if there is a adjustment )?

Sorry for all the questions but i would like to get a "feel" on whats happening.

The same power forward and reflected is one hell of a mismatch and not getting enough power to set the forward power ( from a 4 watt rig) also means a bad mismatch.

Have you tested the magmount with another rig? one assumes that you had another CB on it at one time.

Regards

Bob

[biosurf]

Nope, not pre matched.

Its an 80 channel Uk/Euro handheld I have now tried on UK 1 UK 20 and UK 40 and get the same readings

I didn't tweak the antenna yet as a reading that much off the scale is a groundplane issue rather than length isn't it?

I havent tested the magmount with another rig as that one isn't fitted in the truck anymore and the power cable got torn out by a ####ed passenger!

Tempted to just bite the bullet and try the Cobra but am concerned that if the SWR is that fubarred that it could kill it

As to all the questions.. Christ man don't apologise! You're helping! Ask away.

[g0pey]

Hi

If it was just a ground plane issue then it would only affect you new antenna installation.. not both ( unless that wasnt matched also, hence the reason I asked if it had been tried on another rig)!!

Your handheld generates 4 watts so should generate enough forward power to set full scale on the meter in set position . If it does not then there is a mismatch and it needs to be tweaked .

As a comparison, I use a rig that generated 2 watts and the antenna I use is a
http://www.moonraker.eu/Amateur-Radi...aker-Multiband
multi band and its hell to get matched on 28Mhs ,showing the same symptoms as yours when not matched. Some antennas are right fussy and have a very narrow bandwidth and might not have a good SWR from 26.9 to 27.9 MHZ that your rig covers.

Antenna tweaking is a must in this case.

Regards


bob

[biosurf]

Thanks, I'll try and have more of a play tomorrow (sure the neighbours are starting to wonder why I keep going out to the Surf with a head torch on!)

Thanks for all the advice Bob. Appreciated.

[g0pey]

No Worries..

I just done some quick searching on that antenna .. its well and truly US made so they would have pre-set it ( or near as damm it ) to their channel 19 . Which is far enough off the UK frequencies to give you bother. Having that loading coil at the bottom is going to give you a higher Q factor which in turn with reduce your 1:1 - 1:2 SWR range . If that was set up on the US frequencies then you would have problems with the UK ones.

Good luck

Regards


Bob

[Diezel Weazel]

Blimey Paul a lot a years ago now, but here goes from what I remember we used to check SWR @ channel 1 and channel 40 whatever range ya using they should match similarly n if they don't the antenna needs adjusting up or down (can't remember which tho) till they match or read about the same ...
If in doubt see if ya can borrow another SWR meter, you could be using a fawlty SWR meter ...
Good Luck

Jess
"Cos short cuts can cost more in the long run"

[biosurf]

Thanks Jess. Think I'll buy a new meter, they're pretty cheap.

g0pey any idea if trying the Cobra will have adverse effects. It is a tweaked multi band US rig so may be more forgiving?

[g0pey]

Blimey Paul a lot a years ago now, but here goes from what I remember we used to check SWR @ channel 1 and channel 40 whatever range ya using they should match similarly n if they don't the antenna needs adjusting up or down (can't remember which tho) till they match or read about the same ...
If in doubt see if ya can borrow another SWR meter, you could be using a fawlty SWR meter ...
Good Luck

Jess
"Cos short cuts can cost more in the long run"

Thats good advice..

perhaps this will help

http://www.alpharubicon.com/elect/tuningantennaeli.htm

Regards


Bob

[biosurf]

It is a tweaked multi band US rig so may be more forgiving?

EDITGoing to rephrase this. I don't mean more forgiving but rather as many of the channels are AM etc it may be more suited to the antenna as is.

Thanks for the info - I had read all about antenna tuning and even had the rotary tool ready for trimming it if needs be but most of the tuning docs I had read said that if you are SWRing that far out then its not the ant its something else.

[g0pey]

EDITGoing to rephrase this. I don't mean more forgiving but rather as many of the channels are AM etc it may be more suited to the antenna as is.

Thanks for the info - I had read all about antenna tuning and even had the rotary tool ready for trimming it if needs be but most of the tuning docs I had read said that if you are SWRing that far out then its not the ant its something else.

Hmm.. the cobra is a good rig .. but its tuning range( channels ) is probably going to exceed the available bandwidth of the antenna .. my rig tunes from 28 to 29.5 Mhz and I have to use a matching unit. I cant get away with just the antenna setting on its own . If your cobra has been fully expanded i.e 26 to 30 Mhz then a matching unit will be required. But if you are just using UK 40 then setting just the antenna will do. That loading coil is probably going to restrict you to 500kc or so . A quick check on the US CB frequencies shows it goes from 26.965 to 27.405 which is about 400 kc wide.. Dont expect that antenna to have a 1:1 SWR bandwidth much outside this.

Sorry ....this is way geeky..

Regards


Bob

[charvell]

bio, have you tried running another earth from the mount to the chassis?

[biosurf]

bio, have you tried running another earth from the mount to the chassis?

Hey Charvell. I haven't but if all else fails I'll try. A roof install really shouldn't need that though