[AMRadio] FW: Homebrew receiver

[Brett Gazdzinski]

Don,
That is what I am doing.
Two tuned circuits using B+W coil stock, seems to have a very high
Q, directly into the mixer, out to the Kiwa filter (no loss), into
the IF amps.

It does seem VERY quiet, even with a 'noisy' mixer design.

I have not had any problems with images or broadcast interference,
but I don't tune all over the place, just the AM windows.
Never heard any sort of image, it would be way down with the
high Q tuned circuits...

The new design should be even quieter, if it works otherwise.

The 12sa7 is a pentagrid converter, and both the 6BE6(7pin),
and the 6BA7 (9 pin) tubes look to be replacements.

Brett
N2DTS

 
> The ultimate design for a practical receiver would be single 
> conversion with 
> no rf stage ahead of the mixer.  It would use a selective 
> enough front-end 
> tuning network between the antenna and mixer to reject 
> images, and the mixer 
> would be low noise enough to hear all the way down to the 
> atmospreric noise 
> floor.  The mixer would have high enough output level to feed 
> directly into 
> the selectivity filter with no amplifier stage between the 
> mixer and filter. 
>   Following the filter, the i-f amplifier would be low noise 
> and high gain 
> enough to boost the signal to the level needed at the 
> detector without 
> raising the noise floor above that of the signal that exits 
> the filter.  One 
> requirement would be a selectivity filter with minimal insertion loss.
> 
> One interesting receiver design from before WWII used a 
> separate tuned 
> circuit to null out the image frequency.  It was written up in QST, I 
> believe (or was it RADIO?).  Hallicrafters came out with a 
> model or two that 
> used the design, but it was swiftly discontinued.  I think 
> the problem was 
> that the image null had to be a separate control from the main tuning 
> because of the difficulty of getting the image null to 
> accurately track with 
> the rest of the receiver.  This might be a worthwhile topic 
> to research and 
> apply to a no-compromise homebrew receiver.
> >
> >I am sure there is a tube to replace the 12SA7 in a miniature
> >type.
> 
> Zillions of them were used in the miniature tube version of 
> the classic 
> 5-tube ac/dc bc receiver.  Isn't it a 12BE6? (My computer is 
> in the house 
> and all my radio  reference material is out in the shack).
> 
> Every commercially built receiver, ham or military, is one 
> big compromise, 
> designed to best meet the needs of diverse users.
> 
> Don K4KYV
> 
> _________________________________________________________________
> Is your computer infected with a virus?  Find out with a FREE 
> computer virus 
> scan from McAfee.  Take the FreeScan now! 
> http://clinic.mcafee.com/clinic/ibuy/campaign.asp?cid=3963
> 
> _______________________________________________
> AMRadio mailing list
> AMRadio at mailman.qth.net
> http://mailman.qth.net/mailman/listinfo/amradio