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102" stainless whip

peddler, do you know the magic feed length multiples?
so is it an odd multiple of 18 feet or what? I only ask because i'm in trouble myself. I blew the finals in a 3 week old 2970n2 on a 3 yr old antron 99 with 20 metres of westflex 103 with SWR's at 1.5 at the end of the coax and SWR's at the antenna of 1.2. I had heard of mosfets giving trouble with high swr's so I wasn't suprised.

But what really maddened me was how another install worked.

A neighbour was getting in to cb so he begged a sigma venom aluminium homebase antenna off a relative and couldn't tune it.

(and from what I have read 1/2 wave aerials don't work without a balun and only 1/4 wave and odd multiples of that work like 3/4 wave and 5/4 wave etc so I didn't know how it would work)

I couldn't either no matter whether the antenna was shortened or lengthened feet or inches the swr allways stayed just over 3

I had heard that they didn't work without being mounted on a metal mast(he had it screwed to a timber post) so I hung 3 104 inch radials at 45 degrees from it , no change in swr

Then I opened the antenna and clipped the shorting coil , no change in swr
Then I shortened the mast to 102 inches(from more than twice that) and perfect 1.0 flat swr on high low and mids and 20 feet of rg58.

Im convinced that aerials with a short like the A99 are at fault and cause varying swr on the coax as he just guessed the coax length and setting the aerial up like a 1/4 wave worked better than I could imagine.
(with no fudge tuning)
I can't understand why a brand new a99 could never operate right as before I bought the ranger when I had 170 feet of 75ohm thicknet it had the very same swr as the ideal cable run and yet the roughest antenna install I have ever seen worked perfectly?
You see 18 feet is too short for me as I need a run longer than 20 metres so what run should I use
So please nobody tell me that coax length doesn't matter as I just blew up a box because of it.
 
You will not like this, but coax length does not matter, and 1.5 swr is not high. The swr did not ruin your radio. You have some other problems there.

Sorry.:bdh:
 
I beg to differ. I had read elsewhere on this site that mosfets don't like swr higher than 1.5 and it would explain why so many jackson 2's blowup as very few magmounts have an swr of less than that although if I read a lie then I am writing one.
 
Listen to Packrat ... 1.5 is a decent setting for the CB world, now pureists would want it lower, but it's OK. Coax length is a myth (I'll get flamed for this) but you only need enough to go from point "A" to point "B". Personally in my CB lifetime I have always used a multiple of a 1/4 wave or 9ft...I.E. 9,18,27,36 etc ... but that's just me.

Like Packrat...something else caused your problem and not SWR.
 
Tune the antenna, not the feedline. If you had to tune the feedline, hams would need to have a separate tuned feedline for each band. I have two feedlines in my car; one for HF and one for VHF and above.

Each of the two is exactly long enough to reach from the radio to the antenna.
 
sorry for going off topic so i'll finish here packrat, you were right enough as I keyed the radio into a tuner with the linear switched out and I can see the power needle dropping slowly so it looks like the radio is burning itself out. ah well another box for the scrapheap ;)
 
fodendaf,
There are lots of things written and posted on the internet. If I had to guess, I'd say probably half of what's written is at least being misinterpreted to some extent, incomplete, and probably a mixture of what comes out of the back end of a cow.
There are a number of ways to transform some impedance to another. Some are more efficient than others. Using coax as an impedance transformer is one of those inefficient means of doing that transforming. Why? Because it is almost always destructive to that coax, it's voltage/current ratings are very commonly exceeded. It doesn't mean from a lot of power, just from the normal impedance transformation voltages and currents which can get very high even at very low power levels.
Most of the "truths" you quoted are misconceptions. That 1.5: SWR being "too high" for some solid state devices is one of those misconceptions. A 1.5:1 SWR is not high. And if that solid state device is used in a properly designed circuit, it will work into any SWR, even a really high one. Depends on the designer knowing what he/she is doing.
There are particular lengths (electrical lengths) of feed lines that do have some nice characteristics. The thing there, is if you need whatever that characteristic or not. In most cases, it's probably not needed at all. 9 or 18 feet of coax (any coax) has no particular electrical significance at all. Neither are a 1/4 or 1/2 wave length electrically. The most common reason for including 18 feet of coax with an 11 meter antenna is that it's a length that will typically reach from where ever you'd put that antenna to the radio. It has more practical use than electrical. Wave length is frequency dependent.
There's more, but I just don't feel like writing a book here. I would suggest finding out more about this sort of stuff before putting a lot of faith in what you read. That includes what I write too!
- 'Doc
 
Marconi said:
888, why would you advise rwlack to cut a 102" whip unless he wants to work high in 10 meters? A 102" is already on the borderline of being on the short side for CB.
Click to expand...

With my 96" fiberglass on a spring, in a Hustler C32 ball mount, fed with RG8X / lugs, my SWR was always about ~1:1.3

-Richard-
 
mackmobile43 said:
Yes your ball mount adds roughly 3'' to the over all length of the antenna,
Click to expand...

Yeah, I had it mounted to a stud before. Just a cheapo workman stud with no spring. :LOL:

It was 1:1.1 all over the place. I was a happy man.

Ah well, if anything, the height should put it into the 10m band anyways.

I need to ditch my Palomar 400 for one that can do SSB as well as AM...or mod it for SSB capability.

-Richard-
 
office888 said:
Yeah, I had it mounted to a stud before. Just a cheapo workman stud with no spring. :LOL:

It was 1:1.1 all over the place. I was a happy man.

Ah well, if anything, the height should put it into the 10m band anyways.

I need to ditch my Palomar 400 for one that can do SSB as well as AM...or mod it for SSB capability.

-Richard-
Click to expand...

Well the longer the antenna the further away from 10 meters you're gonna be, you see 10 meters is less than 11 meters so the antenna will be shorter.
 
damn that lou franklin!


lied to me again! LOL

so, you're saying its not because the fiberglass whip has a copper wire in it, and electricity moves through stainless steel and copper at different speeds?
LC
 

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