[TowerTalk] 160m Shunt Feed

[Stan Stockton]

I think you meant to say shorter instead of longer in the second  
sentence and then to say you can use one capacitor if the electrical  
length of the structure is a quarter wavelength or more?

Kelly - How tall is the tower, what antenna is installed on top and  
are the guy wires insulated from the tower?

Stan, K5GO

Sent from Stan's IPhone



On Dec 11, 2010, at 7:49 PM, "Gene Smar" <ersmar at verizon.net> wrote:

> Kelley:
>
>     The two-capacitor matching system is probably the Omega match.   
> This
> matching system is typically used on towers that are longer than 1/4
> (electrical) WL.  Most of us mere mortals are confined to feeding  
> shorter
> towers.
>
>     If that is the case, you can most likely use a single capacitor of
> appropriate voltage rating as part of a Gamma matching system.  This  
> is a
> single large gauge wire (think CATV coax sheath) or a wire cage of  
> several
> parallel wires supported off the tower by a couple of feet or even  
> more and
> tapped onto the tower somewhere near the top.  The capacitor  
> (usually a
> transmitting variable but can also be a fixed value, once the proper  
> value
> has been obtained) is connected at the bottom of the tower between  
> the end
> of the shunt wire/cage and the center of the coax cable.  The coax  
> shield is
> connected to the tower itself and to the radial system emanating  
> from the
> tower.
>
>     Once you have the wire tapped and capacitor connected, you start  
> the
> game of adjusting the cap for minimum SWR, then changing the tap  
> point on
> the tower if you can't get the match low enough.  This may take a  
> few trips
> up and down the tower before you get a decent match.
>
>     You can check out KB9CRY's tower and shunt feed at
> http://nidxa.org/kb9cry_shunt_fed_tower.htm   .  Mine is pretty  
> similar
> including the wire cage on PVC supports off the tower.
>
> 73 de
> Gene Smar  AD3F
>
>
>
> ----- Original Message -----
> From: "Kelley" <kshaddrick at jetup.net>
> To: <towertalk at contesting.com>
> Sent: Saturday, December 11, 2010 6:57 PM
> Subject: [TowerTalk] 160m Shunt Feed
>
>
>> Multitudes of web pages show, well, multitudes of setups for shunt  
>> feeding
>> a tower. Many appear to use a couple of variable capacitors in  
>> order to
>> adjust for lowest SWR. Having a limited junk box, what kind of parts
>> should I be looking for to build a generic matching network?
>>
>> Thanks,
>>
>> Kelley
>> _______________________________________________
>>
>>
>>
>> _______________________________________________
>> TowerTalk mailing list
>> TowerTalk at contesting.com
>> http://lists.contesting.com/mailman/listinfo/towertalk
>
> _______________________________________________
>
>
>
> _______________________________________________
> TowerTalk mailing list
> TowerTalk at contesting.com
> http://lists.contesting.com/mailman/listinfo/towertalk