BIG clean GREEN
Well-Known Member
I assume something to do with transmitting radio frequencies !
Nick.
Nick.
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CB Antenna
- Thread starter Julian
- Start date
BIG clean GREEN
Well-Known Member
Thanks Jon, I'll give it a go !
Nick.
Nick.
I have to say that looking at it Nick (earlier today) I am not convinced about ground plane and these gutter mounts. Maybe they are fine, but you've basically nothing under your aerial but some plastic and glass.
Any experts out there, come back.. bleep.
Rubber Duck
Any experts out there, come back.. bleep.
Rubber Duck
Gutter mounts are not ideal but Nick should still be able to get acceptable performance for his needs. What's under the antenna does matter, as well as what's along side it, so e.g. middle of the roof is better than half way down a rear quarter panel but it depends where you want to find the balance between performance and convenience. Those stinger antenna seem to be little better than a 50ohm dummy load but someone will come along in a minute to tell me they get 50 miles on theirs 
BIG clean GREEN
Well-Known Member
I ended up cutting a further 1.75" off the aerial, and now I have readings of :-
- 1.1 on Ch 01
- 1.2 on Ch 40
The aerial is right at the bottom of the base at that, so now an happy bunny,
Nick
p.s I've got a local CB club man making me up a ground plane gadget to further improve reception for the gutter mount !
- 1.1 on Ch 01
- 1.2 on Ch 40
The aerial is right at the bottom of the base at that, so now an happy bunny,
Nick
p.s I've got a local CB club man making me up a ground plane gadget to further improve reception for the gutter mount !
Richard Jackaman
Well-Known Member
- Joined
- Apr 6, 2010
- Messages
- 246
I've got a Sirio 4000 gutter mounted half way along my 80. It's mounted on a Sirio gutter mount which clamps firmly into the gutter using a couple of alan screws.
Without cutting the antenae I get a SWR of 1.1 on Ch 1 and 1.2 on Ch 40. The whip is mounted as low in the coil as possible. Get the same sort of readings when replacing the Sirio with a (uncut) stinger although never used that in anger.
The Sirio seemed to perform well when uses on the Strata Florida run during the Lincomb weekend. Well it did from my perspective, all reception was clear and I assume transmissions were fine. Jon? Not that we were ever very far apart on that trip.
Gutter mounting in general will skew the ground plane and you get relatively low performance from the side that it's mounted. The performance is better over the roof from the mount. So mounting it halfway along on the passengers side gives acceptable performance to the front, back and drivers side of the vehicle and comprimised performance to the passengers side. At least that's my understanding.... which may be flawed
Cheers
Without cutting the antenae I get a SWR of 1.1 on Ch 1 and 1.2 on Ch 40. The whip is mounted as low in the coil as possible. Get the same sort of readings when replacing the Sirio with a (uncut) stinger although never used that in anger.
The Sirio seemed to perform well when uses on the Strata Florida run during the Lincomb weekend. Well it did from my perspective, all reception was clear and I assume transmissions were fine. Jon? Not that we were ever very far apart on that trip.
Gutter mounting in general will skew the ground plane and you get relatively low performance from the side that it's mounted. The performance is better over the roof from the mount. So mounting it halfway along on the passengers side gives acceptable performance to the front, back and drivers side of the vehicle and comprimised performance to the passengers side. At least that's my understanding.... which may be flawed
Cheers
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None central mounting does skew the radiation pattern a bit but the real world effect is marginal and I really wouldn't go to any great lengths to achieve it.
BIG clean GREEN
Well-Known Member
So Jon, I assume my readings are pretty good now ?
Nick.
Nick.
As far as the SWR is concerned your readings are very good Nick and if you have any range problems now I would look elsewhere. SWR doesn't tell the whole story but it's the easiest thing for you to measure and should do for a decent antenna without getting silly about it 
@ Richard - your transmissions were very clear to me. I've been on plenty of trips where a stinger struggled to do better than a few car lengths
@ anyone who breaks their Sirio - the casting can snap at the base of the whip if caught low enough on a branch but the casting is threaded and screws into the base and could be replaced with a steel version if you have access to a lathe. That's what I've done on the 4000 that goes on my front bumper as it's more exposed. The 3000 on the rear wheel carrier has the original casting still.
@ Richard - your transmissions were very clear to me. I've been on plenty of trips where a stinger struggled to do better than a few car lengths
@ anyone who breaks their Sirio - the casting can snap at the base of the whip if caught low enough on a branch but the casting is threaded and screws into the base and could be replaced with a steel version if you have access to a lathe. That's what I've done on the 4000 that goes on my front bumper as it's more exposed. The 3000 on the rear wheel carrier has the original casting still.
Paul
Well-Known Member
After fitting my CB now its time for the antenna, i have a mouting as i want to fit it to my roof bars but obviously this does not give a good contact to ground.
As mentioned on this thread, should i give a clean ground to the vehicle body via a lead or something similar?
As mentioned on this thread, should i give a clean ground to the vehicle body via a lead or something similar?
BIG clean GREEN
Well-Known Member
I had a roof bar mount on mine initially but the reception/transmission was poor, since then I purchased a gutter mount which is much better !
Are we talking about the OEM roof rails Paul? They're quite well grounded being an alloy casting bolted into the roof and have always worked well when I've mounted an antenna on them.
Paul
Well-Known Member
Put some thule roof rails on and mounted antenna.
Trying to do swr as per Crispins guide
but getting very eratic readings.
The first part goes ok when adjusting "set" but then needle goes all over the place, then moving onto the next bit the needle sits a bit under 2 but then goes weird again.
Is my SWR meter knackered? Or do i need to ground the rails as would have thought this would just be a bad reading rather than eratic.
I am also plumbing meter in along antenna cable as i joined it to extend length. Bit tricky to get the meter in on back of cb.
Trying to do swr as per Crispins guide
but getting very eratic readings.The first part goes ok when adjusting "set" but then needle goes all over the place, then moving onto the next bit the needle sits a bit under 2 but then goes weird again.
Is my SWR meter knackered? Or do i need to ground the rails as would have thought this would just be a bad reading rather than eratic.
I am also plumbing meter in along antenna cable as i joined it to extend length. Bit tricky to get the meter in on back of cb.
- Joined
- Mar 7, 2010
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- Country Flag
When I worked as a radio tech, we always mounted antennas directly through the roof in order to avoid such problems. Normal position would be in front of the roof rack. Often straight over the domestic light, to make things easier. If mounted with care, with a quality antenna and a non-acid sealant, it would last as long as the rest of the car.
Only if a car needed a temporary comms-radio for a day or a week, we would mount the antenna on a bracket on the gutter or rail, and it would work good enough for a day or two. Or use a magnetic mount.
I've never done it with a cross-bar on roof rails, but it should be possible to get enough grounding for the antenna up there to.
Whatever you mount the antenna on which is not considerably bigger than the antenna, will act as a part of, and an extension to, the antenna.
For grounding, when it comes to radio waves, one can not think in terms of electric grounding. It is not the same. Good electric connection is not good connection for the signal to the antenna. Think area -- the wider the ground straps are, the better. So for a roof rack/bar, I would connect each end of the bar (or each leg of the rack) to the body of the car with a wide copper strap, while ensuring good metallic connection at each end. Now this is not very practical on a car, so one has to compromise. If, e.g, you use several small straps spread apart, it is nearly as good a a single strap with the same width as the distance between the two straps furthest apart. Which ever way you try, make sure both ends of the bar is well grounded.
One practical way could be to hide the ground points inside the brackets of the bar and rails. Thinking of the rails of my 100: The feet of the rails are fastened with small bolts into the roof structure. If we add some tooth lock washers, it would be good. Next, the rail-foot is made of some kind of alloy which doesn't connect very well to the steel tube rail, so a stainless screw/bolt with the same toothed washer could connect the two parts. Then comes the bar to rail connection, which is normally by a clamp with a rubber sleeve. Now, if we get some kind of spikes in between the clamp and the rail, that penetrates into both, several at each end, it could work. Some kind of sealant would have to be added to prevent corrosion. Something similar between clamp and bar? (Can't see how they are joined right now) --- This could be my aproach if I had to mount a GP antenna on a roof bar.
Still, the bars and rail would be a part of the antenna; but the biggest problem is if they are only partly part, because of lacking or bad grounding -- some kind of floating disturbance between antenna and ground.
This is written as an attempt to provide better understanding if the problems regarding the mounting of GP antennas on vehicles. If you look at the lcool site, they have quite a bit of info. The aussies have more experience in this matter than most.
Good luck, and keep us posted
Only if a car needed a temporary comms-radio for a day or a week, we would mount the antenna on a bracket on the gutter or rail, and it would work good enough for a day or two. Or use a magnetic mount.
I've never done it with a cross-bar on roof rails, but it should be possible to get enough grounding for the antenna up there to.
Whatever you mount the antenna on which is not considerably bigger than the antenna, will act as a part of, and an extension to, the antenna.
For grounding, when it comes to radio waves, one can not think in terms of electric grounding. It is not the same. Good electric connection is not good connection for the signal to the antenna. Think area -- the wider the ground straps are, the better. So for a roof rack/bar, I would connect each end of the bar (or each leg of the rack) to the body of the car with a wide copper strap, while ensuring good metallic connection at each end. Now this is not very practical on a car, so one has to compromise. If, e.g, you use several small straps spread apart, it is nearly as good a a single strap with the same width as the distance between the two straps furthest apart. Which ever way you try, make sure both ends of the bar is well grounded.
One practical way could be to hide the ground points inside the brackets of the bar and rails. Thinking of the rails of my 100: The feet of the rails are fastened with small bolts into the roof structure. If we add some tooth lock washers, it would be good. Next, the rail-foot is made of some kind of alloy which doesn't connect very well to the steel tube rail, so a stainless screw/bolt with the same toothed washer could connect the two parts. Then comes the bar to rail connection, which is normally by a clamp with a rubber sleeve. Now, if we get some kind of spikes in between the clamp and the rail, that penetrates into both, several at each end, it could work. Some kind of sealant would have to be added to prevent corrosion. Something similar between clamp and bar? (Can't see how they are joined right now) --- This could be my aproach if I had to mount a GP antenna on a roof bar.
Still, the bars and rail would be a part of the antenna; but the biggest problem is if they are only partly part, because of lacking or bad grounding -- some kind of floating disturbance between antenna and ground.
This is written as an attempt to provide better understanding if the problems regarding the mounting of GP antennas on vehicles. If you look at the lcool site, they have quite a bit of info. The aussies have more experience in this matter than most.
Good luck, and keep us posted
Paul
Well-Known Member
Ok,
Also looking at a mag mount option and found this as dont want to go too high, i am reading that sirio is pretty good.
http://www.ebay.co.uk/itm/Sirio-ML145MA ... 564074ca57
Also looking at a mag mount option and found this as dont want to go too high, i am reading that sirio is pretty good.
http://www.ebay.co.uk/itm/Sirio-ML145MA ... 564074ca57
eratic readings would suggest a problem with the plugs or cable somewhere or the output from the CB being eratic. Are you trying this with the CB set to UK FM channels? AM will be erratic depending how much noise you make while the mike is keyed
Paul
Well-Known Member
Right then, after getting a new SWR meter, the readings are now making sense but still way too high.
Tried the adjustment both ways on grub screw so now it is antenna shortening (mag mount single metal rod) but the question is by how much?
The first "set" adjustment is fine but the other is off the scale.
Tried the adjustment both ways on grub screw so now it is antenna shortening (mag mount single metal rod) but the question is by how much?
The first "set" adjustment is fine but the other is off the scale.
