[Amps] RF Chokes

Peter Voelpel df3kv at t-online.de
Wed Jul 19 09:30:09 EDT 2006


Rohde&Schwarz did that from the fifties on in their SK050, SK080 and SK1
transmitters. Actually they were using two of them at right angles in their
SK1, where one is shorted out on the higher frequencies.
The SK050/080 upper limit was 24MHz, while the SK1 is 1.5-30MHz.
I do the same in a homebrew all band amp with 2xRS1072C

73
Peter


-----Original Message-----
From: amps-bounces at contesting.com [mailto:amps-bounces at contesting.com] On
Behalf Of Kenneth D. Grimm, K4XL
Sent: Mittwoch, 19. Juli 2006 15:09
To: wc6w at juno.com
Cc: philc at texascellnet.com; amps at contesting.com
Subject: Re: [Amps] RF Chokes

wc6w at juno.com wrote:
>> -- "Phil Clements" <philc at texascellnet.com> wrote:
>>     
> <snip>
>
>   
>> Harris has been doing this for years in their amps. The RF->110, 
>> (pair of 4CX1500B's) has a plate choke that is a very small ferrite 
>> loaded unit that is clean from 1.8-30 mhz. This was the ideal fix 
>> for adding WARC bands and 160 meters, but the amateur amp 
>> manufacturers did not pick up on this.
>>
>> <snip>
>>
>>     
>> (((73)))
>> Phil Clements, K5PC
>>     
>
>   

Would it be possible to have a look at the photos that you took of the 
choke and parasitic suppressor arrangement that you posted on  
www.pixhost.com/pixp/philk5pc/Platechoke.jpg but which are no longer 
available?

> Hi Phil,
>   If I recall correctly, that choke is listed on the schematic at 
> 115uH.
>
>   Employing the ferrite core should place the first (parallel) 
> resonance suitably above 30 MHz.
>
>   This appears to be a valid approach because of the low plate 
> impedance (circa 1000 ohms).  Though there will still be plenty of 
> reactive current through that choke on the lowest bands.
>
>   Still a compromise, albeit a less objectionable one than 
> most "amateur" amps.
>
>   I'm feeling just a bit of deja vu all over again. :-)
>   To see why, start at this old link:
>
>    http://lists.contesting.com/_amps/2000-03/msg00603.html
>
> 73 & Good evening,
>   Marv WC6W
>
> http://wc6w.50webs.com/
>
>   
Actually, it makes pretty good reading...all over again.   ;-) 


73,
-- 

Ken K4XL
k4xl at arrl.net

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