Whip it good

[ghutch]

bonding is a key element...I think to getting the antenna to "couple" if you will to the earth under the auto. Make the auto as a whole act as like a coupler?
My swr is not the same all the time....as i move from a rocky or dry sandy area it is higher.....get on the beach 50 feet from the saltwater it is lower....and works Much better.
i'm sure someone here can explain it MUCH better.....does the cab act as a capactor ? a question for some of the more knowledgable
read the KOBG site
a help to bonding ....make a small test wire with a alligator clip on both ends...short one about a foot long. clip it to good grounded spot that is bonded to the chassis and then move it from place to place under your hood to screws, brackets,fuel injectors and brackets, exhuast tubing on both sides, hood hinges to fenders bolts on the firewall....clip it to any and everything....one bracket on my firewall made a huge impact and cleared out the injector noise completely. experiment clip it all over!! you will see a good reduction in noise levels from place to place....if it reduces noise then bond that joint...I went crazy, hoods both sides to fenders, they in turn to chassis, all doors to cab, cab to chassis(rubber mounted cab)4 places, exhaust tubing in front of the cat. converter and behind on both sides, engine to chassis etc......bonding dropped my noise on a new radio install from s5-6+ to s1-2 most days. if i park at a quite location my noise is many days pegged to the left....all i hear is the atmospheric hiss. i have appro. 20 or so straps on my tacoma.....it was a pain to install but well worth the effort. Good Luck

 

[The DB]

bonding is a key element...I think to getting the antenna to "couple" if you will to the earth under the auto. Make the auto as a whole act as like a coupler?

Close. The body of the car and the ground beneath it act like a capacitor, thus the car is capacitively coupled to the ground beneath the car. There is a bit more that goes into it, but getting the whole vehicle to work as one unit is the goal.

My swr is not the same all the time....as i move from a rocky or dry sandy area it is higher.....get on the beach 50 feet from the saltwater it is lower....and works Much better.

The conductivity of the earth ground will have an effect on the antenna. Different surfaces have different properties, and in the real world it doesn't get much better than salt water.

i'm sure someone here can explain it MUCH better.....does the cab act as a capactor ? a question for some of the more knowledgable

Anything relatively close to the antenna will have an effect. The cab will add capacitance to the antenna which will throw off the resonant point. To counter that you need more inductance, which you get by lengthening the antenna.

Moving the antenna further away from the cab will lessen this effect.


The DB

 

[3puttbob]

Everyone's suggestions have been most helpful. I shortened the bracket for strength. I added 2 ground straps underneath the mount area from bed to frame and frame to cab. I removed the spring. I have an SWR of 1.4:1 on 40 and 1.6:1 on 1. Which makes me tempted to add the spring but, NOT. I'm beginning to believe that, like it is mentioned a little further on, is the whip is too close to the cab. Not sure where I want to go from here. My only test equipment is a Dosy meter for output and SWR, another SWR meter and the usual volt meters.

 

[jazzsinger]

Everyone's suggestions have been most helpful. I shortened the bracket for strength. I added 2 ground straps underneath the mount area from bed to frame and frame to cab. I removed the spring. I have an SWR of 1.4:1 on 40 and 1.6:1 on 1. Which makes me tempted to add the spring but, NOT. I'm beginning to believe that, like it is mentioned a little further on, is the whip is too close to the cab. Not sure where I want to go from here. My only test equipment is a Dosy meter for output and SWR, another SWR meter and the usual volt meters.

first thing i'd be doing is getting that swing kit (what do you need that for?) checked for harmonics/ripped out, you'll never get an accurate swr reading if the radios spewing harmonics, and you would never know if they were present as none of your meters can differentiate from a clean signal and one full of harmonics.

secondly i'd be looking for a better mounting position, like the centre of the roof, anywhere else is poor by comparison and will effect the radiation pattern.

just like a power meter can read higher/lower when harmonics are present, so can swr meters,

 

[purenrg]

Why would anyone modulate while checking there Swr? Harmonics has nothing to do with a dead key.

 

[jazzsinger]

Why would anyone modulate while checking there Swr? Harmonics has nothing to do with a dead key.

not much point having a good swr when you key up if it jumps to 10:1 the minute you talk, unless ofcourse you are masochistic about buying hard to source and pricey rf transistors after its blown the arse out of your amp/radio or both.

but hey as long as your swr is good when you key up everything must be A ok.

i won't even mention the risk of losing your equipment through causing rfi before it all blows.

 

[3puttbob]

The 2 to 14 watt swing made a difference in modulation clarity. My SWR swings to 1.6:1 when I dead key at 1.2:1. I took off the whip and put on my old penetrator type coil. Match is fine but, still need the 10" extension. Must be the cab interference.

 

[W5LZ]

Checking SWR when speaking is silly, it just doesn't work that way. Calibrating the meter involves setting the max power limit and making a comparison with the returned power. If you change the forward power by speaking, which is totally normal, then the calibration is then off. It requires a constant and non-changing power to do that checking. The same holds true with the self-calibrating meters, they are just faster to compensate for power variations. They will also 'wiggle' a bit in their readings.
- 'Doc

 

[jazzsinger]

Checking SWR when speaking is silly, it just doesn't work that way.

i'll bow to your superior knowledge, even though i think you missed my point.

i wan't suggesting checking swr while modulating, although if the signal was clean the extra power from swing would do nothing to change swr (it would still have the same fwd to ref ratio), whereas a dirty signal would have its harmonic content reflected hence a higher swr, yeah i may have exaggerated 10:1 but my point is still the same.

far to many people put too much importance on swr, without even grasping the concept of resonance, adjusting for best swr won't necessarily give best performance. especially if an antenna isn't 50 ohms by design (about 99.9999999% of antennas, yeah another slight exaggeration)

 

[W5LZ]

If those harmonics are reflected then they have to have been part of the forward power also. I would think the ratio, hence the SWR, would still be the same.
- 'Doc

 

[jazzsinger]

If those harmonics are reflected then they have to have been part of the forward power also. I would think the ratio, hence the SWR, would still be the same.
- 'Doc

you sure?

hypothetical scenario:

100w transmitted on 27 mhz into 1.0:1 swr, = zero reflected/100w transmitted.

same 100w forward power, say 80w for talking sake is at 27mhz and 20w of harmonics is at multiple other frequencies (bear in mind your swr meter isn't too smart when it comes to frequency, come to that neither is the power meter) both into an antenna that previously showed 1.0:1 swr, do you think it will still show 1.0:1 swr ?

it will at 10w at 27 mhz, it will at 25w at 27mhz, it will at 37w at 27mhz, but will it when you add fwd power at other unwanted frequencies the antenna isn't resonant on?

 

[W5LZ]

Your hypothetical situation isn't going to hold water because there are several factors that you have no way of identifying/proving.
How do you know that you have any harmonics at all? You're right, that meter can't identify them.
If your transmitter is producing any harmonics and you increase/decrease power, it is much more likely that those harmonics are going to increase/decrease at a constant rate. That means that the same percentage of the output signal will be harmonics and the SWR -ratio- would not be affected by them. The equipment to discover harmonics is not all that common, there's no 'simple' way of determining their presence. If you happen to have the required equipment and do find significant harmonics present, then cure the problem and get rid of them. That seems like a very good thing to do, right?
SWR is not a sign of having harmonics.
A change in SWR means that there's a change in impedance, or that the meter isn't calibrated correctly for the power level being used, but only -IF- there is no other physical/electrical change in the antenna system. A lot of things can affect impedance, but harmonics is only one of them, and certainly not the most common one.
- 'Doc

 

[3puttbob]

If you hold a steady modulation and re-calibrate the swr, then flip to test, You get what you started with 1.2:1