[AMRadio] RE: Receiver update.

[Brett Gazdzinski]

Carl,
I started with the schematic for a Scott model SLRM.
I used that because it has a 455 KHz IF, and because it works very
well for a 1930's receiver.

I ran afoul of the Local Oscillator which uses a tapped coil
setup, and I needed to use ceramic slug tuned coil forms
that don't deal well with taps...only two lugs, small, 
close wound turns, etc.

Since a local oscillator can be any configuration, I used
a parallel coil and cap setup out of the Bill Orr handbook
(14th edition, page 496, cw man's receiver).
No extra feedback coils or taps.

The S meter circuit came out of the Bill Orr 15th edition,
page 542, high performance amateur band receiver.
Values had to be experimented with to get it to read in range,
sensitive enough, etc.

The detector I got from something I printed out off the web,
A low distortion AM detector,
http://www.zianet.com/wb5lhv/amdetector.jpg

I don't know if that is still a good link....

To get the AGC voltage (not shown on that detector) I did
some playing around with the cold end of the output
side of the last IF transformer...a resistor and a pot
to ground, voltage developed across the resistor/pot combo.

I was very lucky to have some tube type adaptors around.
I removed the top 9 pin tube sockets and mounted the slug tuned coils
inside, with the wires out the 8 pin octal plug on the bottom.
There is also provision for grounding the can through the octal plug.

I could just as well have mounted the coil forms on the chassis
and added a switch to select bands...maybe I should have,
but the receiver was very experimental and I figured I could 
unplug the coil assembly and play with it, try different ideas
and coil types, etc.

For the RF amp, its a 3 turn link input, one side goes to the
antenna, the other to ground, then there is a resonant coil
on the same form with a vari cap across it.

I used big ceramic coil forms because I did not want
to cut and trim a lot of expensive B+W coil stock.
You want hi Q coils here.

The tuned input circuit goes to the rf amp grid, the plate
circuit goes to another coil and cap setup, the cap is
ganged (dual section SHIELDED cap).
The second coil is a slug tuned one so it can match the input coil
inductance...these coils and caps cover both 80 and 40 meters
without me having to change anything, other bands would require
a coil change.
The cap wound up being slightly small at 140pf to cover both
bands, its all the way open on 40, all the way closed on 80.

I may change it later when I find one with a wider ratio
that fits in the mounting space...


Shielding can be important, and I ran all of the IF signals
in shielded wires.

The IF cans mount in octal tube bases.
Its easy to mount a tube socket and plug anything into it,
mounting PC board mount IF cans (what I have) would be tough.
I can try different IF transformers, mechanical filters, etc.
by just plugging them in....


The L.O. has things mounted very rigidly, the wire connecting
things is #12, very stiff for stability.
I pulled plates out of the tuning cap to get the frequency range
I wanted, about 150 KHz from one end of the dial to the other.

I soldered the plates I pulled out of the cap across the tube sockets
(underneath) to shield the input and output sides...grounded the
shields.

The spectrum analyzer was invaluable in checking frequency, gain,
harmonics, etc.
I could not have gone as fast without it, and might not
have managed to get things working correctly if I did not have it.


I did the front panel and final assembly today, it turned out 
very good. I will use it for a while before painting it.
Its black as it is, but not shiny or labeled yet...

Brett
N2DTS


> -----Original Message-----
> From: amradio-admin at mailman.qth.net
> [mailto:amradio-admin at mailman.qth.net]On Behalf Of Carl Nord
> Sent: Sunday, February 17, 2002 8:16 PM
> To: amradio at mailman.qth.net
> Subject: Re: [AMRadio] RE: Receiver update.
> 
> 
> There used to be a HBR site, but I cannot find it. Anyone 
> know where it is?
> Bret, What was the "core rcvr" you started with. I am 
> thinking of following
> your path with some parts I have.
> Carl
> 
> WA1KPD
> Visit My Boatanchor Collection at 
> http://pages.cthome.net/nord/wa1kpd.html
> 
> ----- Original Message -----
> From: "Brett Gazdzinski" <brett.gazdzinski at wcom.com>
> To: <amradio at mailman.qth.net>
> Sent: Sunday, February 17, 2002 7:59 PM
> Subject: RE: [AMRadio] RE: Receiver update.
> 
> 
> > Scott,
> > http://www.kiwa.com/
> >
> > Brett
> > N2DTS
> >
> > > -----Original Message-----
> > > From: amradio-admin at mailman.qth.net
> > > [mailto:amradio-admin at mailman.qth.net]On Behalf Of Ka9p at aol.com
> > > Sent: Sunday, February 17, 2002 8:24 AM
> > > To: amradio at mailman.qth.net
> > > Subject: Re: [AMRadio] RE: Receiver update.
> > >
> > >
> > > Brad - I've only been intermitantly following this thread
> > > (but enjoying it -
> > > I'm collecting HBR16 parts) - is there a link to the source
> > > of the Kiwa
> > > filter modules? Thanks< Scott
> > > _______________________________________________
> > > AMRadio mailing list
> > > AMRadio at mailman.qth.net
> > > http://mailman.qth.net/mailman/listinfo/amradio
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> >
> >
> 
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