I agree about folk legend. I just ran the numbers through my
calculator, and I may have to eat crow as far as shortening the coax.
In this particular case, qa quarter wave on 1.8 comes out at 95 feet, a
no no for sure. If you don't want to cut or shorten the coaax, try
adding some just to see if anything changes. I never heard of a magical
don't number, but it is possible. In this case, though do a 492 over 2
for a quarter wave, divided by freq, 1.8 or whatever, and times .7 for
volocity factor and my calculator says 95 feet if I did it right.
73
Butch
WA0VJR
Node 3148
Wallace, ks.
On Thu,
17 Nov 2011, Pat Byrne wrote:
> Tom,
> I've never heard any magic about 100 feet. Perhaps it is an urban
> folk legend!!
> I don't have anything that will tune 160 at all properly but will try
> to listen as the saga goes on!!
> Having a little trouble finding antenna installer support but someday!!
> Pat, K9JAUAt 07:42 PM 11/17/2011, you wrote:
>> Guys:
>>
>> I unexpectedly had some extra time here tonight, and just got off 160 meters
>> with some midwest hams, who gave me a real interesting theory about my 160
>> meter sloper, the excess coax I'm using for a feed line, and why it might be
>> throwing my SWR's off.
>>
>> Here's the theory:
>>
>> They said that using a 100 foot piece of coax as a feed line is never a good
>> idea because there is something in that particular length that is known to
>> throw antenna resonance off. They said there was an article in QST
>> documenting this fact a number of years ago.
>>
>> They said that what I want is either a half wave-length piece of feed line,
>> or an eighth-wave length piece of coax. They say I should avoid a
>> quarter-wave piece.
>>
>> If you do the math (i.e. 468 over the frequency in megahertz), a half-wave
>> piece of coax would be approximately 260 feet long. This is obviously not
>> very practical.
>>
>> However, if one were to use an eighth-wave piece, that would amount to
>> approximately 65 feet long.
>>
>> Since I seem to have about 40 extra feet of coax out in my yard at the base
>> of the antenna, cutting that off would almost give me that eighth-wave
>> length.
>>
>> I wonder if this is really what I should now shoot for.
>>
>> Of course, I do not have experience soldering pl259's, so I'll have to get
>> help there, but I'm really thinking this might be worth a try.
>>
>> You guys know far more about this stuff than I do, so if you think this
>> theory is nuts, please don't hesitate to let me know.
>>
>> Thanks for the continuing help with this issue, and I look forward to
>> working at least some of you on 160 meters around 1.845 MHZ tomorrow night.
>>
>> 73 from Tom Behler: KB8TYJ
>>
>> ----- Original Message -----
>> From: "John Miller" <[log in to unmask]>
>> To: <[log in to unmask]>
>> Sent: Thursday, November 17, 2011 7:31 AM
>> Subject: Re: SWR's continued
>>
>>
>>> All I can say is that did happen to me the one time I coiled up about 50
>>> feet of coax, it actually made it try to radiate the rest of the coax and
>>> the SWR went crazy. The coax was fine, I cut off the extra and used it
>>> elsewhere later on, even uncoiled and thrown all over the place it was
>>> fine
>>> but coiled up, it wasn't happening at all. I'm just reminded of that which
>>> is why I say that.
>
>
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