[AMRadio] FW: Homebrew receiver

[Brett Gazdzinski]

Yes, its been quite some time since I had the NC300 and NC303!
No 455Khz IF at all?

80 KHz is quite low, and should do real well in the IF,
but its not easy to get the mechanical filter shape out of
tuned circuits, they tend to be pointy at the top.
My G76 uses a 262Khz IF, and it works quite well, but they used
resistors across the IF transformers to lower the Q, and small caps
from primary to secondary to shape the response.
Quite a good receiver except for the fidelity.
I added a small 4 watt IC chip audio amp, replacing the 
modulator driver/audio output setup they used, and get quite good
fidelity.
Its easy to change the receive bandwidth, increase the resistor value
makes it sharper, as does removing the little caps from
primary to secondary.
The shape is another matter...
 
The transmit audio is a bit hopeless, small iron, sweep tubes as
modulators (in some crazy triode connection using the screens as grids),
but feedback helps.

Got to love the dial on the NC300/303, what a nice piece of
work that was.
Quite a good receiver now, great in its day.

My favorite style was the Collins 75a series, 32v series, the kwm2
type look, and the Hallicrafters SX17/SX28 type look.
I think the Gonset G76 also looked very sharp, one of the few
Gonset things that looked nice, some was quite odd.
I always had a thing for the TMC GPR90, thought it looked
quite nice, but never had one.

One project that I have not go to yet is to get a 75s1 and
do it up for AM.
A hi fidelity detector, external audio amp, and a KIWI
filter in place of the back to back IF cans would give
you a stable, accurate, reliable, small good sounding receiver.
  
Brett
N2DTS 

> -----Original Message-----
> From: amradio-admin at mailman.qth.net
> [mailto:amradio-admin at mailman.qth.net]On Behalf Of Grant Youngman
> Sent: Thursday, October 16, 2003 11:06 AM
> To: amradio at mailman.qth.net
> Subject: RE: [AMRadio] FW: Homebrew receiver
> 
> 
> > 
> > As far as the NC303/300 goes, if you can get past the style,
> > the only big improvement to be done would be the audio output
> > (if used), and maybe the addition of a KIWI filter module.
> > These are quite like mechanical filters, very sharp.
> > One of those would be very easy to add, without hacking
> > up the receiver.
> 
> 
> Not everyone will agree with you on the "style" issue ... I like it!
> 
> Unless KIWI has started making filters at 80 Khz, this isn't 
> an option.  The 
> 303 is 2Khz wide in the SB1/2 positions, and has 3.5 and 8Hhz 
> positions 
> for AM.  Skirt selectivity is pretty typical of the L/C IF 
> arrangement.
> 
> The downsides I've found in both the 300 and 303 include BCB 
> feedthrough on 80 (solved by using a KIWI BC reject filter in 
> the antenna 
> lead), and SWBC feedthrough on 20M at night.  There's an internal 
> tunable trap to null that out, but it isn't terribly 
> effective.  Same in the 300 -
> - although for some reason the 303 manual doesn't say 
> anything about it 
> even though it's in there.
> 
> Grant/NQ5T
> 
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