Pete KE9OA wrote:
I hope I didn't sound too negative in my last
reply.............actually the 394 isn't a bad receiver.
For those who might be interested, I can redesign the
input filters, using a 3 branch chebychev topology. Just
shoot me the filter limits that are given in the service
manual, and I can do that. It will turn a fair receiver
into a very good receiver. I won't charge for this
service........there are enough of you out there that can
benefit from it!

Hi Pete, I'm interested. I have been intending to build an outboard set of
filters that would be diode switched under the control of the receiver, just
as the internal filters are controlled. Was thinking of doubling the number
of filters to narrow the individual passbands for even better protection
from overload. Would control this sub-band switching by comparison against
the voltage applied to the varactor. As I have never designed and built this
sort of thing before, I'd be happy to have your guidance. I'll e-mail you
off list with the frequencies.

Tom

That sounds good, Tom. I do have a 7 band presector up on my website, that I
use in one of my general coverage designs, but the cutoff frequencies would
be a little bit different. The service manual for the 394 has the band
ranges. On one of my 394s, I did remove the MW/LW loopstick and replace it
with 3-branch Chebychev filter sections. It worked very well. I ended up
selling the receiver for the same 100 dollars I paid for it. When I ran into
the fellow at the following hamfest, he told me that he had sold his
original 394 and kept mine, so I think that he was happy with it.
Actually, the 394 is a pretty good design.......................once you
replace those front end filters, you have a pretty good receiver. I am not
sure what kind of filter switching diodes that receiver uses, but HP 1N5767
PIN diodes work pretty well. Any PIN diode that has a 1.5uSec minority
carrier lifetime is good for the 100kHz to at least 30MHz range. The main
thing that you need to do is use biasing chokes that are self-resonant at
the highest frequency for each filter section. That's ok...................I
have a parts selection manual that lists the SRF of the generally used
chokes.
Once again, all I need are the CF of the filter sections, and the F_low and
F_high, and we are all set!

Pete

Tom Holden wrote in message
...
Pete KE9OA wrote:
I hope I didn't sound too negative in my last
reply.............actually the 394 isn't a bad receiver.
For those who might be interested, I can redesign the
input filters, using a 3 branch chebychev topology. Just
shoot me the filter limits that are given in the service
manual, and I can do that. It will turn a fair receiver
into a very good receiver. I won't charge for this
service........there are enough of you out there that can
benefit from it!

Hi Pete, I'm interested. I have been intending to build an outboard set of
filters that would be diode switched under the control of the receiver,
just
as the internal filters are controlled. Was thinking of doubling the
number
of filters to narrow the individual passbands for even better protection
from overload. Would control this sub-band switching by comparison against
the voltage applied to the varactor. As I have never designed and built
this
sort of thing before, I'd be happy to have your guidance. I'll e-mail you
off list with the frequencies.

Tom

Pete,

What's your website address?

Pete KE9OA wrote:

I do have a 7 band presector up on my website...


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http://home.att.net/~n.gianakopoulos...ome.html-.html

The above link will take you there. I do have the radio design files and the
Marshall Leach stereo preamp in .ZIP form.
When you open up the radio file, you will have PDFs of the schematics, parts
placements, etc. I also have both the source code and the hex file for the
DDS. Have fun!

Pete

"starman" wrote in message
...
Pete,

What's your website address?

Pete KE9OA wrote:

I do have a 7 band presector up on my website...


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