[ARC5] Selectivity and the BC-455

[Kenneth G. Gordon]

On 24 Oct 2014 at 5:21, DSP3 wrote:

> Ken,
> 
> Now that's a new twist on the subject.  Truth told, I have never seen a 
> single-coil ARC-5/274-N receiver, but then again, its only recently that 
> I've been actually disassembling them.   If there is only one coil, no 
> wonder the selectivity is "less than what might be desired".   Which 
> manual carries that design, if you or anyone can pass on?

I don't know which manual has schematics of this issue, so I will have to go 
try to dig those out. But I CAN show all and sundry photos of such a can.

I'll have to dig THAT can out too.

I know I was very surprised to find this issue when I began my investigation 
of how to improve the selectivity of our favorite receivers. I had planned the 
exact same solution that you came up with, and at the time, due to the 
almost non-existent selectivity of the "40 meter" receivers, I started with that 
one.

In addition, in that youtube video by Mike Murphy WU2D, a link to which I 
posted here, Mike mentions that the 2830 KHz IF cans HE first disassembled 
also had only one coil, and is the reason he built the crystal-filter.

So, I am not "blowing smoke". It is simply a fact.

As a matter of fact, the very first 2830 KHz IF can I ever disassembled had 
only one coil. From that, I deduced, incorrectly as it turns out, that ALL 2830 
KHz IF cans had one coil, and is the sole reason I switched my efforts to the 
receivers which have 1415 KHz IFs. 

Therefore, I was more than a little surprised to find that you worked the same 
magic on your 2830 IFs that you had on the 1415 KHz IFs.

In fact, I was actually quite satisfied with the selectivity of the 3 - 6 MHz 
receivers, since I spend most of my time on CW. In my opinion, they work 
just fine for that mode. They are a little broad, but still acceptable and 
useable.

The 6 - 9.1 MHz receivers are another story...

Ken W7EKB