[TowerTalk] Increasing power capability of 6-meter Yagi

[Tim Duffy]

Hello Mark,

Also - remember that all of the Cushcraft power ratings were posted before FT8. 
The FT8 duty cycle (almost 15 seconds key down) can be hard on antennas and amplifiers if you intend to run power.

73
Tim K3LR
-----Original Message-----
From: TowerTalk [mailto:towertalk-bounces at contesting.com] On Behalf Of Mpridesti via TowerTalk
Sent: Sunday, July 31, 2022 11:25 AM
To: Joe Subich, W4TV
Cc: towertalk at contesting.com
Subject: Re: [TowerTalk] Increasing power capability of 6-meter yagi

Joe

You make perfect points here!

No doubt the gamma was designed around a KW power level but the reality is, it was probably ok for 500 watts. Power limit was 1 KW input with 50% efficiently, a 500 watt design target was the case. Now envision 1500 output to the antenna feed point. Yep you will have problems!

Other related Cushcraft power limits come with the A3/A4 tribanders- no more than 1200 watts here. 

Regards,

Mark, K1RX


> On Jul 31, 2022, at 9:51 AM, Joe Subich, W4TV <lists at subich.com> wrote:
> 
> 
>> On 2022-07-31 9:01 AM, Pete Smith N4ZR wrote:
>> It looks to me that this limitation might relate to the feedline connection, which is a bulkhead SO-239 (mounted with a big nut) bracketed to the center of the driven element.
> I would bet that the limitation is due to the breakdown of the
> dielectric in the gamma match (capacitor).  CushCraft used a
> rod from the center conductor of the UHF connector through a
> dielectric tube inside an aluminum tube that formed the outside
> of the gamma match.
> 
> If 1KW is a real limitation, I doubt that you can do anything
> to improve it except redesign the antenna for a split driven
> element and 50 Ohm feed.  That 7' boom would make a nice 4 element
> OWA.
> 
> 73,
> 
>   ... Joe, W4TV
> 
>> On 2022-07-31 9:01 AM, Pete Smith N4ZR wrote:
>> I have just bought a small Cushcraft 3-element 6-meter yagi.  Only small fly in the ointment is that it is *only* rated at 1 KW.  It looks to me that this limitation might relate to the feedline connection, which is a bulkhead SO-239 (mounted with a big nut) bracketed to the center of the driven element.
>> My question is, do I need another connector here, or maybe insulation between the bracket and the element?  If so, what material makes sense? Any other advice?
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