When I see such lines as:
It is not an old wives tale,
that a poorly made choke will fail
and
to avoid burning your hair,
park your resonances with care
I see something poetic just behind the grid dip meter.
C'mon, where are the poets when we need them.
Colin K7FM
-----Original Message-----
From: Will Matney <craxd1@verizon.net>
Sent: Aug 26, 2005 8:28 AM
To: amps@contesting.com
Subject: Re: [Amps] plate choke
On 8/26/05 at 4:00 AM R.Measures wrote:
>On Aug 26, 2005, at 12:48 AM, Alex Eban wrote:
>
>> The main problem stems from the 160 meters operation!
>> For the higher bands, chokes are usually in the range of 68 to 100
>> microhenries. These are easily wound in a solenoid manner and if you
>> space
>> wind the last 20 turns or so, chances are you get a choke without
>> resonances
>> in the ham bands. On the other hand for 1.8 MHz operation the coil
>> inductance goes up in the millihenry range: a lot of turns, crammed
>> together. This is prone to parasitic resonances and usually you will
>> find
>> that the better amplifiers DO NOT include the top band, or else, they
>> have
>> some queer arrangement, like two chokes in series or some oddly wound
>> choke.
>> I remember very well the one made by Barker and Williamson , wound in
>> sections, each on of a different number of turns.
>
>I tested this idea by winding two chokes, One had a continuous
>single-layer, and one had various gaps as per the Handbook. The
>inductances were about the same and, to my surprise, so were the
>resonances. This led me to conclude that end-to-end coils do not
>decouple unless the gaps are quite substantial.
>-- For maximal decoupling, chokes need to mounted at right-angles.
>-- For maximal coupling, chokes need to be mounted end-to-end.
Exactly! I always thought those coils were still way too close together to do
any good. The gaps are only around 1/4-1/2" apart. The theory I'd say is
correct, but the design was wrong. That can be proven using a dip meter running
either paralell or at a right angle to a coil under test. At a right angle, the
dip meter wont couple and work.
>
>> At some time Collins used
>> them in military radios that covered 2 to 30 MHz continuously. I don't
>> know
>> whether someone is making them today. This was on of the main reasons
>> that
>> in military equipment (high power!) they dispensed with the choke and
>> moved
>> over to series feeding of the high voltage supply. The GRC 106 was one
>> good
>> example. It employed series feed of the 2400 VDC supply and took the
>> power
>> out through a link on the coil.
>> Alex 4Z5KS
>>
>> --
>> No virus found in this outgoing message.
>> Checked by AVG Anti-Virus.
>> Version: 7.0.344 / Virus Database: 267.10.15/81 - Release Date:
>> 8/24/2005
>>
>>
>> _______________________________________________
>> Amps mailing list
>> Amps@contesting.com
>> http://lists.contesting.com/mailman/listinfo/amps
>>
>
>Richard L. Measures, AG6K, 805.386.3734. www.somis.org
>
>_______________________________________________
>Amps mailing list
>Amps@contesting.com
>http://lists.contesting.com/mailman/listinfo/amps
_______________________________________________
Amps mailing list
Amps@contesting.com
http://lists.contesting.com/mailman/listinfo/amps
_______________________________________________
Amps mailing list
Amps@contesting.com
http://lists.contesting.com/mailman/listinfo/amps
|