[ARC5] Command Set Field Day

[hwhall at compuserve.com]

 I like the little add-on boxes since there's no need to molest the radio with new holes and labels. I've always been fond of small projects too; they appeal to the lazy part of me.

Wayne
WB4OGM



-----Original Message-----
From: Bill Cromwell <wrcromwell at gmail.com>
To: hwhall <hwhall at compuserve.com>
Cc: arc5 <arc5 at mailman.qth.net>
Sent: Tue, Jan 1, 2013 4:28 pm
Subject: Re: [ARC5] Command Set Field Day

 
 
 
On Tue, 2013-01-01 at 17:35 -0500, hwhall at compuserve.com wrote: 
> > 
> The selectivity of the 40 meter receiver is much too broad (purposely) and  
> really can't be much improved on, although it is certainly fun to use. 
> > 
>  
>  Would a simple Q-multiplier help the selectivity enough? I see a 1-transistor  
(old PNP type) Q-mult in the 1964 ARRL Handbook. Battery powered and a single  
coax lead to an i.f. tube plate. The article was for a 455-500 kHz i.f. but that  
can be altered I imagine. 
>  
> Wayne 
> WB4OGM 
 
Hi Wayne, 
 
I will probably have the chance to find out before much longer. I have 
been thinking the same thing here. I think the separate Q-multiplier 
might be a little more effective or at least more stable than adding 
Q-multiplication to an IF amp. That has been said by other hams who have 
tried both ways. The reason might be that changing the Q affects 
amplification and varying the IF gain affects the Q setting. When they 
are separate there is little interaction. Either means would be helpful. 
I like sprinkling little solid state pills in boxes of tubes to help out 
in that kind of way. I might be more inclined to use an FET in *this* 
century (evil grin). It won't be necessary to make holes or other 
permanent mods to the radio. 
 
I have a new toy here..a scaf filter. Specifically the NEScaf version. 
I'm going to build a couple more of them. I already plugged it into the 
audio of an ARC-5 and it makes a huge difference. There is no single 
thing we can do that will fix everything that annoys us. That scaf 
filter does a lot though. The NEScaf does most of what a Select-O-Ject 
does. It's prevented from serving as an audio oscillator but we can set 
the center frequency in the "bandpass mode" and we can vary the amount 
of peaking (short of oscillation). At it's narrowest the NEScaf has an 
audio bandwidth less than 100 cycles (specified at ~90 Hz). At it's 
widest it will pass AM quite nicely. NEScaf also does not employ the 
notch filter but that IS available on the chip if a guy wanted to use 
it. With a 100 Hz knothole the notch hasn't been needed. 
 
73, 
 
Bill  KU8H