[ARC5] ARC-5/274-N SAelectivity - separating IF coils

[J Mcvey]

 When I modified the IF transformer in the ARC-5 receiever, I re-arranged the internal ceramic spacers to put more distance between the coils..It did improve the selectivity a little, but I never did an "official" test of the resultant bandwidth. 
 Maybe the open turn to ground is worth a try.A shorted turn would probably kill the Q of the transformer. 


    On Sunday, September 27, 2020, 5:53:56 PM EDT, Kenneth G. Gordon <kgordon2006 at frontier.com> wrote:  
 
 On 27 Sep 2020 at 21:20, Hubert Miller wrote:

>    Where was this published?

At least two places that I know of: most recently, in ER Mag. I can dig out the date and issue 
number if you wish to have it.

It was also mentioned in, I believe, one of Gordon White's articles which covered ARC doing 
this after WWII to reduce the bandwidth for users other than military.

>    There is a Youtube video of a 'Command Set' upgrade where a crystal is added into one IF can in 
>    a clean, nonobtrusive, fixed setting crystal filter.

Yes. That was Mike Murphy WU2D who did that. His videos are very interesting and highly 
entertaining. He is very sharp.

> This would have to have been the  6 - 9

It was.

> as the crystals  are more readily found.

Well, I sure had trouble finding any...still haven't found any...

> I seem to recall this set's IF is around 2830 kHz

Correct.

> and there was an old AM boat - band crystal for channel ( I think )
> 2837 kHz which in FT-243 will fit into the IF can.  In the video, the
> filter actually did give single -sideband, "single signal"
> selectivity. Cute. Of course, there is still a rather fast tuning rate
> to deal with, but it seemed from the video to be workable. -Hue Miller  

OK. Well, as I said, I have not yet found a crystal in that range.

In addition, there is a sort of a problem with the 6-9 MHz receivers in that there are two very 
different types of IF cans: one type has only one large coil, while the other type has the usual 
two coils, one of which can be moved.

To reply to Dennis, I have modified the IF cans in one of my BC-454 receivers before I had 
read of someone doing it in ER Mag. I had read the article in which ARC had done this, and 
remembering how the IF selectivity is increased in the BC-453, and R-23 and R-24 receivers, 
I thought I would try it in the others.

Works well, but can be a lot of work.

Ken W7EKB
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