[ARC5] ARC 5 reciever backlash and selectivity...

Sun Apr 23 11:30:47 EDT 2017

On 23 Apr 2017 at 14:34, J Mcvey via ARC5 wrote:

> 
> Trying to get everything in shape, but I'm getting frustrated with the ARC-5 
> receiver's touchy tuning.
> 1) no selectivity

Yes. On 40 meters the selectivity is essentially non-existent. 80 meters is at least useable. 

There are two common solutions, one OK, the other very good. 1) add regeneration to the 
1st IF stage (there was an article in QST on this), or 2) use a BC-453 with a converter. 

http://www.w7ekb.com/glowbugs/rx/NoviceQ5er/NoviceQ5er.pdf

One guy also changed the 1st IF can on a 40 meter receiver into a single-crystal filter with 
good results. You can see all this on youtube. Trouble is finding a 2830 kHz crystal is not 
easy.

An audio filter can also help. I have several of the CWF-2 audio filters which I use. MFJ has 
them as a kit.

> I am marginal at CW as it is, but when I have to hear two or three different tones 
> at the same time it makes it nearly impossible for me.

Yes. That was true for all of us back then.

> 
> 2) backlash.
> I haven't taken the receiver apart yet to look at the mech.
> Any suggestions before I do?

As I mentioned in a reply from my Android, the internal mechanism has ZERO backlash, but 
if you are using ANY of the military knobs, there is very significant backlash. None of those 
fit tightly onto the spline. There is a lot of slop.

Again, cut a 1" long piece of 1/4" diameter hard-brass tubing, using a dremel with cut-off 
wheel, cut two thin slots parallel to the length of the tubing in one end and opposite to one 
another about 3/8" long, drive the modified tubing with the slotted end over the spline shaft, 
center it up, then attach any good knob.

Viola.

No backlash.

Ken W7EKB

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