The type of antenna doesn't matter, the quarter wave really has nothing 
at all to do with the anteenna.  A quarter wave stub looks open if 
shorted and shorted if open.  On other frequencies, it is a short, dc or 
anywhere, for example one cut for 27 would be a half wave at 54 and 3/4 
wave at 81 meg.
73
Butch
WA0VJR

On Fri, 8 Apr 2011, colin McDonald wrote:

> I see, ok.
> Do you think this type of thing can help on bass stations using a vertical
> style antenna?  or does it mainly only help mobile installations that
> receive QRN caused by wind, dirt and that get build ups of static
> electricity from the antenna moving through the air?
> also, using a quarter wave DC stub might help to eliminate RFI caused by
> certain frequencies I would presume?  Say if you were causing your neighbors
> home stereo to practically explode on 7 megs, would a properly tuned stub
> for 7MHZ help to eliminate this issue along with a balun, chokes and low
> pass filter of course.
>
> I'm just wondering what other practical applications a quarter wave dc stub
> could be used for other than the application for 27 meg mobile installations
> that you mentioned.
> does having the stub connected on a T reduce the amount of rf getting out to
> the antenna? or does the open/closed aspect of having both the dc stub and
> the regular antenna on the load prevent this?
> also, does this only work when you are using a quarter wave antenna?
> presumably, you could cut the stub to match what ever type of radiator you
> are using?
>
> 73
> Colin, V A6BKX
> ----- Original Message -----
> From: "Butch Bussen" <[log in to unmask]>
> To: <[log in to unmask]>
> Sent: Thursday, April 07, 2011 6:28 PM
> Subject: Re: antenna lengths
>
>
>> It gives the antenna a dc ground, so the static is sent right to ground.
>>  At 27 mhz, the stub appears open, an open quarter wave appears shorted,
>> and a shorted quarterwave appears open.
>> 73
>> Butch
>> WA0VJR
>>
>> On Thu, 7 Apr 2011, colin McDonald
>> wrote:
>>
>>> and I bet   the antenna was matched better to the radio with that stub
>>> connected?
>>> I get that it helped to reduce static build up or something, but how does
>>> a
>>> quarter wave stub do that?
>>> 73
>>> Colin, V A6BKX
>>>
>>> ----- Original Message -----
>>> From: "Butch Bussen" <[log in to unmask]>
>>> To: <[log in to unmask]>
>>> Sent: Thursday, April 07, 2011 5:22 PM
>>> Subject: Re: antenna lengths
>>>
>>>
>>>> The 468 comes in to play as dipoles have what is called an end effect of
>>>> around 5 percent.
>>>> I'm not sure where the formula for the loop comes from but if you're
>>>> figuring say a quarter or half wave stub, you use 300 meters which is a
>>>> full wave length and the speed of light.  To convert this, take meters
>>>> times 3.28 so 984 over frequency gives youa full wave length.  for a
>>>> quarter wave stub, for example, divide this by 4 and then that number
>>>> times the volocity factor of your coax.
>>>>
>>>> Way back when I was selling a lot of cb rigs, and people were running
>>>> quarter wave whips, 102 inches long.  These ghings would pick up enough
>>>> static here in a dirt storm, you could lay the pl259 on the dash and
>>>> sparks would jump from the center pin to ground.  Needless to say, this
>>>> was hard on fet transister front ends, so her was my fix.  I would
>>>> divide
>>>> 984 by 27 mhz, which comes out 36.444 and 36.44 divided by 4 for a
>>>> quarter
>>>> wave in feet is 9.111.  The coax I used which was rg58 had a volocity
>>>> factor of around .7 as I recall, so 9.111 times .7 is 6.377 feet.  I'd
>>>> make this stub, short one end and put it on a t connector on the radio
>>>> with the antenna to the other leg.  It was a dc short, but as a quarter
>>>> wave looks open at its frequency, the radio didn't know it was there.
>>>> Worked like a champ!!
>>>>
>>>> 73
>>>> Butch
>>>> WA0VJR
>>>
>>>
>>
>
>