Whatever wavelength you have computed must be multiplied by the velocity
factor of that feedline, in coax very good LMR400 has a velocity factor
close to 90% as I recall, and regular coax is I thought 75% but when I
looked it up on-line, it is more like 66%.
Where you should have studied velocity factors in your ham theory section is
if you need to make matching transformers on the feedline. This is the
principle used in the shortened G5RV antennas.
----- Original Message -----
From: "Tom Behler" <[log in to unmask]>
To: <[log in to unmask]>
Sent: Thursday, November 17, 2011 9:19 PM
Subject: Re: SWR's continued
> So, steve, how does the 75% velocity factor fit into the wave-length
> calculations for the feed line?
>
> I just do not recall that piece of information from when I studied for and
> passed my Extra class license back in 1997.
>
> 73 from Tom Behler: KB8TYJ
>
> ----- Original Message -----
> From: "Steve" <[log in to unmask]>
> To: <[log in to unmask]>
> Sent: Thursday, November 17, 2011 3:04 PM
> Subject: Re: SWR's continued
>
>
>> Tom,
>>
>> If you coil up excess coax, it may act as an RF choke. If you wind five
>> turns or so, it is often referred to as a "poor man's balun". It is not
>> a
>> bad idea to wind five turns or so at the connection to a beam or dipole,
>> the
>> choke will help prevent some signal from radiating back along the skin or
>> shield of the coax, if there is a significant reactive load at the
>> antenna.
>>
>> I rather doubt that you derive any similar benefit with coiled coax at
>> the
>> base station. However, it is pretty likely that if you cut out a hunk,
>> you
>> will notice some change in your SWR. Remember though, the velocity
>> factor
>> of typical coax is around 75% if I recall correctly.
>>
>> Steve, K8SP
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