Open coil spacing

[boomer111]

With my Predator 10K antenna what will the coil spacing between turns as well as the overall coil length effect when altered.

I used to be R-50 X-0 but now am R-58 X-0 and am wondering if my touching up the coil spacing has affected the readings.

Hit a low branch and the coil was shoved off center, I centered it and equally spaced the distances between the coils but have no idea the overall length of the coil or effects thereto.

Just trying to track down why my ohms is off. I have new coax coming too. The change did come after my homemade ring terminal coax was used.

Both events happened around the same time, so I am not sure which is responsible.

Just trying to understand more.

Thanks

 

[M0GVZ]

The gauge of the wire used, the diameter of coil and the turns and the spacing of the turns all affect the inductance of a coil.

At 58 Ohms I wouldn't worry. Shortening the length of the coil should reduce the impedance.

 

[W5LZ]

The diameter of the coil, the size of the conductor used to make that coil, and the spacing between turns of that coil all have an affect on how much inductance the coil has. The size of the conductor has an affect on how much current the coil can handle. To really raise the current capacity the diameter of the conductor typically has to really get larger. The spacing between coil turns affects the over-all current capacity/power level the coil will handle without shorting between coil turns. Keeping the shape of the coil uniform, not bent, etc, tends to prevent a change in the ratings of the coil. A smaller spacing between a couple of turns of that coil could affect the inductance and power handling of the coil (more prone to short?).
As far as the change in the 'R' from 50 to 58 ohms... forget about it, it just isn't going to make any difference in performance. And as for that new coax? It's your money, waste it however you want. New coax isn't going to make anything 'better'.
- 'Doc

A 50'R'-0'X' gives a 1:1 SWR. That 58'R' -0'X' would be a 1.1:1 SWR. That is NOT a significant change, and isn't bad at all. Why waste good worry on it?

 

[boomer111]

Ok, I did mess with the MFJ 259 a bit while messaging the coil.

Right, I did not change the Ohms but the center of the swr curve did move.

Hell for that matter so did the direction I was parked in change the reflect coefficient reading on the advanced mode.

I was figuring that maybe my soldering skills, when adding the terminal ends cause a bump or somehow changed the coax properties effecting the ohms.

This meter has always been influenced with the direction of my vehicle regarding the Sun (I assume it is the Sun influence) in the reading in the advanced mode under reflect coefficient. The -db reading, and from my research the larger the minus number the better. So I tend to tune using this mode selection, no reason really.

 

[The DB]

In a mobile environment a car passing 30 feet away can affect the antennas tune, not to mention the changing of the quality of the earth under the vehicle as it moves, other cars or the lack thereof in the vicinity, or moving the vehicle a few feet or less, or even turning the car to face the other direction...

Did I mention the weather? (How is the weather near you btw, its freaking cold here...) The temperature, the humidity, rain ect. These can also affect the tune... Should I go on?

Long story short, don't fret over minor changes in your antennas tuning in an ever changing environment, lest you get caught up in a never ending cycle of minor changes to maintain a perfection that will never be.

Luckily, when it comes to antennas close is good enough, and getting closer to some magic variables really doesn't make any difference.


The DB

 

[boomer111]

I understand this from my own experiences with the 259B.

I tend to be a perfectionist, mostly because it is a challenge.

Used to spend hours on hours messing with the antenna on the mobile.

 

[M0GVZ]

And how much of a difference did you really notice? If you didn't have the antenna analyser would you have known?

Just to add something to the mix...

The MFJ 259B can be affected by nearby transmitters when its plugged into an antenna. Go park near a paging tower and when the they transmit you can see the frequency on the readout jump.

 

[Captain Kilowatt]

And how much of a difference did you really notice? If you didn't have the antenna analyser would you have known?

Just to add something to the mix...

The MFJ 259B can be affected by nearby transmitters when its plugged into an antenna. Go park near a paging tower and when the they transmit you can see the frequency on the readout jump.

My former boss in the broadcast biz couldn't use the MFJ analyzer at home to tune the VHF antennas he built. He was practically in the shadow of a 100 kilowatt FM site. To add insult to injury it was one of "ours". LOL He used to come out to my place to some antenna work.

 

[boomer111]

And how much of a difference did you really notice? If you didn't have the antenna analyser would you have known?

Ya you are right, in the real world it didn't change anything....but I knew and that is what is important.

Just knowing my station was in fine order and sounding good, with no problems other than the dozens of busted truck antennas and broken antenna mounts, grounding out.

This was the hardest part in the big rig. We did a lot of off road work. No super slap driving here.

 

[M0GVZ]

Yeah I was lucky in so much that all of mine was on the black stuff. The downside was that I was an agency driver so could be in five different trucks for five different companies in a week so it was magmount thrown on the roof and a bit of wood with the CB bolted to it thrown on the dash.

When I did used to do the off road stuff it was in big 100 tonne earth movers in quarries such as the Terex and Volvos and they were so loud you couldn't hear a CB anyway.