[HBR] New member from Brazil

[Dave And Merrijoy]

Hey Walt,
Good to see you posting again.
I always enjoyed your military articles in ER.
Dave w9ocm

----- Original Message ----- 
From: "Walt Hutchens" <waltah at earthlink.net>
To: "HBR Receiver List" <hbr at mailman.qth.net>
Sent: Monday, August 31, 2009 5:37 PM
Subject: Re: [HBR] New member from Brazil


> Carlos said:
>> Like I said, the biggest problem here is to find all the parts, mainly a
>> adequate variable capacitor, trimmers and the dial.
> 
> A few things occur to me.
> 
> 1. Vacuum tube auto radios were often built with 262 kcs IFs, thus
> junker auto sets from the 1950's-60's might be a source.
> 
> 2. Ham band only tuning (but not band imaging) is obtainable with the
> main tuning cap from an FM receiver, in the U.S., 88-108 Mcs.  Again,
> a junk set might provide what you need and (possibly) a dial mechanism
> that could be adapted.
> 
> 3. If you do 80-40M lband imaging with an IF of 5500 kcs (or so) -- this
> requires a crystal filter of some sort, OR double conversion -- then
> the 1st oscillator tunes 1500-2000 kcs. This is easily done with the
> main tuning cap from a junk BC receiver. Don't knock this setup for
> stability, either: The oscillator is very high-C and if well designed,
> will drift something like 1 kcs before you do any sort of temperature
> compensation and require no voltage regulation.
> 
> The front end -- which tunes ~3500-7300 kcs to select the band -- can
> be tuned with a second BC cap.
> 
> I have a set with this design which uses a push-pull oscillator
> driving a push pull mixer (both dual triodes) to give single-end IF
> output.  The oscillator is so solid that I am using AGC on the mixer
> as well as the two IF stages without pulling that's noticeable on SSB.
> With three controlled stages, the AGC performance is excellent and
> with no RF stage and a triode mixer, there's no problem with front
> end overload.
> 
> This design does have a spurious response where the third harmonic of
> the oscillator passes through the 5500 kcs IF.
> 
> You could use a 2nd IF of 262 kcs using three auto radio IFTs and get
> tolerable performance -- perfectly adequate for AM, or (with audio
> filter) CW.  This would require one IF stage at 5500 with fairly high Q
> coils to control images.
> 
> Or using a half-lattice crystal filter (IF can be shifted slightly
> according to what you can find) you can get excellent selectivity
> without another conversion and extra stage. There are MANY kinds of
> WW-II surplus crystals in that range.
> 
> I agree with Ian that the Super SimpleX and 2X4+1 designs are a useful
> starting point.
> 
> Welcome aboard, Carlos!
> 
> Walt
> KJ4KV
> 
> 
> 
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