EMRFD Message Archive 1923

Message Date From Subject
1923 2008-08-12 00:14:40 Adrian Scripca Hybrid Cascode IF Amplifier input network questions
Hello all,

I would like to accommodate a hybrid cascode if amplifier offered by
KA7EXM to the IF of 5.068Mhz. The source impedance is the output of a
200 ohm crystal filter. I used an online calculator in order to rework
the input L matching network.

For 200 ohm source resistance, 3000 ohm load resistance ( 0 reactance )
and 5.068Mhz operation frequency, I get L = 23.5uH and C = 40pF. Here's
a couple of questions :

Q1 : Are my calculations involving 0 reactance correct ?
Q2 : Do I also need to rework Q5 collector's T1 ? Leaving it the way it
is but lowering the operation frequency would reduce its reactance,
therefor we shall get less voltage swing which further gets divided by 4
( transformer turn ratio ). Can this be overlooked ? Am I missing
something ?
Q3 : In case the calculations are correct, would it be alright to use a
type 43 ferrite toroid for L1 ? ( I'm thinking of 7 turns on a FT-37-43 )

Thank you,
Adrian, YO6SSW
1934 2008-08-13 06:44:20 Tom Hall Re: Hybrid Cascode IF Amplifier input network questions
Hi Adrian,

Since no one else responded and I'm building the same radio as you (
http://www.partsandkits.com/fluxbb/index.php ), I say your
calculations are correct. I measured the impedance using the method
described on this page
http://www.mitedu.freeserve.co.uk/Theory/inzoz.htm
and came out pretty much on the money after building mine. I used a
powdered iron core with about 65 turns (if I remember correctly). I
can see why you would want to use ferrite for only 7 turns. The
general rule of thumb is to use powdered ir
1939 2008-08-14 10:16:11 Wes Hayward Re: Hybrid Cascode IF Amplifier input network questions
Hi Adrian, et al,

One quick comment. I think that the other folks have checked your
calculations regarding the L-network and they are fine. However, you
do NOT want to use any available ferrite core, especially the -43
material, for this inductor, for the loss can be very high. The -43
material is really bad in this regard. This is not a problem with
wideband transformers in a low impedance environment, but an inductor
on this core in a tuned network would not work well. On the other
hand, a -61 or -63 material core might work fine. You can always use
a powder iron toroid. Or look in the junk box for RF chokes. They
often do just fine.

Good luck.

73, Wes
w7zoi
1965 2008-08-18 09:42:59 Adrian Scripca Re: Hybrid Cascode IF Amplifier input network questions
Hi Wes and Tom,

Thank you for your input. I've been a bit busy lately and didn't get a
chance to set things straight with the hycas amplifier. After some
thinking I decided to use a molded choke and if that fails I'll try a 61
material core toroid. Glen was also kind in offering advices regarding
the posted questions so I'd like to thank him aswell.

As Tom mentioned before, I'm building the same radio he's building using
W8DIZ modules and NorCal DDS and hycas IF amp.

Thank you all for your input.
73 de Adrian, YO6SSW


Wes Hayward wrote:
> Hi Adrian, et al,
>
> One quick comment. I think that the other folks have checked your
> calculations regarding the L-network and they are fine. However, you
> do NOT want to use any available ferrite core, especially the -43
> material, for this inductor, for the loss can be very high. The -43
> material is really bad in this regard. This is not a problem with
> wideband transformers in a low impedance environment, but an inductor
> on this core in a tuned network would not work well. On the other
> hand, a -61 or -63 material core might work fine. You can always use
> a powder iron toroid. Or look in the junk box for RF chokes. They
> often do just fine.
>
> Good luck.
>
> 73, Wes
> w7zoi
>
>
>
>
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