[ARC5] Receiver Filter Adaptor- From Pillar, Back to Post

[Bruce Long]

Hi Mike:
Yes it is obvious adding a low frequency receiver connected to the 1st IF and thereby introducing (at least) another conversion and tighter selectivity will improve the performance of a HF ARC-5 receiver.
With respect to making the ARC5 receiver into something it is not, there is ample discussion over the last 5 decades of methods to narrow the selectivity of Arc-5 HF receivers.  From this you can assume there is a sizable body of interest in making the receiver something it is not, at least by some people to at least some extent.  As such discussion of this topic is not beyond the veil.
Of course tighter receiver selectivity places increased demands upon receiver tuning rate and frequency stability however these receivers in a benign indoor, temperature stable and vibration free- at least in comparison to a WW2 prop aircraft in flight- can cope with some modest selectivity improvement.  Being able to tune the main tuning knob without gloves helps as well.

It is also a simple, easily removable mod to add a small value varactor across the LO oscillator section of the main tuning capacitor giving a few KHz of band-spread for precise tuning.
In this way a lot of the performance advantage of the ARC-5 Triple Superhet can be had in a single receiver.   






      From: Mike Everette via ARC5 <arc5 at mailman.qth.net>
 To: "arc5 at ix.netcom.com" <arc5 at ix.netcom.com>; "gumbear at pacbell.net" <gumbear at pacbell.net>; "arc5 at mailman.qth.net" <arc5 at mailman.qth.net>; "boatanchors at minime.theporch.com" <boatanchors at minime.theporch.com> 
 Sent: Thursday, February 18, 2016 2:46 PM
 Subject: Re: [ARC5] Receiver Filter Adaptor- From Pillar, Back to Post
   
I've been following this thread with interest; but sort of wondering why anyone would make a Command receiver into something it ain't.  Unless you band spread the receiver, the tuning rate is very fast for use with high selectivity crystal filters.
Look on the ARRL QST Archive and check out an article called "An ARC-5 Triple Superhet" from the late 1950s.  This scheme works very, very well and the low frequency receiver can be used as a passband-tuning device.
Same basic idea was found in Volume 3 of the Surplus Radio Perversion Manual.
73
Mike
WA4DLF

      From: "arc5 at ix.netcom.com" <arc5 at ix.netcom.com>
 To: gumbear at pacbell.net; arc5 at mailman.qth.net; boatanchors at minime.theporch.com 
 Sent: Thursday, February 18, 2016 11:26 AM
 Subject: Re: [ARC5] Receiver Filter Adaptor- From Pillar, Back to Post
  
 

 Sent from my ain't-so-smartphone.
------ Original message------From: Arden AllenSubject:Re: [ARC5] Receiver Filter Adaptor- From Pillar, Back to Post
>Where is the screen grid bypass capacitor? I'm the original circuit, the screen bypass is the .1uFd on the bottom left, next to the 100k pull-down resistor.  V1 is powered from the screen buss.
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