[TowerTalk] Using Stubs to Reject Harmonics

[Rex Lint]

Jim,

SB-220 is similar to Kenwood 922 - both use pi network.

    -Rex-

     Rex Lint, Consultant
     26 Brek Drive
     Merrimack, NH 03054
     PH:    603-860-7651    


-----Original Message-----
From: towertalk-bounces at contesting.com
[mailto:towertalk-bounces at contesting.com] On Behalf Of Jim Brown
Sent: Wednesday, February 03, 2010 4:04 PM
To: Tower and HF antenna construction topics.
Subject: Re: [TowerTalk] Using Stubs to Reject Harmonics

On Tue, 2 Feb 2010 13:49:36 -0600, Tim Duffy K3LR wrote:

>Hi Jim:

>I always wanted to test the 1/4 wave "insertion" theory, but never got
>around to it. I would love to hear what the difference is - if you can
>experiment.

Tim,

I haven't done any measurements, but I did do a literature search of QST 
product reviews to learn what output circuitry is used by power amps that 
you and I are likely to be using. What I learned is that MOST, but not 
all, use the pi-L output configuration -- starting from the tube, shunt C, 
series L, shunt C, series L. This configuration allows stubs to be placed 
at the output of the power amp. Amps that use this configuration include 
the original Ten Tec Titan 425, Alpha 374, 76, 77, 87, 91B, ACOM 1000 & 
1010, Ameritron AL-800H, and QRO-2500DX. The AL-82 and AL-1200 use a pi-L 
on 160 and 80, but pi network on the other bands. 

I can't find reference to the output network of the current model Ten Tec 
Titan III, the Alpha 86 or 89, the ACOM 2000, Heath SB-1000 or SB-220, 
Ameritron ALS-600, or Tokyo High Power products. If I were guessing, it 
would be that they follow suit of other products in their heritage. The 
Commander HF-1250 and HF-2500 have a pi-network to match the tube to 200 
ohms, then a 4:1 toroidal xmfr. From a network point of view (that is, 
interaction with stubs), I'd call it a pi. 

The Ten Tec Herc II and Centurion, the Kenwood TL-922A all use pi 
networks. 

73,

Jim K9YC  


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