[ARC5] Selectivity and the BC-455

[Joel R Roberts]

Hello Ken and Brian, On page 171, figure 42 shows the graphic of the 
BC-455-A IF cans as only having one coil in all three cans. These are 
the diagrams for the 2830kc IF cans 7277, 7278 and 7279 on the part 
numbers. Alos in looking at the tables in Gordon White's article 
"Command Set Receivers for All Frequencies- The Easy Way" it shows the 
ARC-5 models have 2 coils while the 274-N 6-9.1, 9-13.5, 13.5- 20 and 
the 20-27 all have only one coil in the IF cans. Lower Frequency IF cans 
have 2 coils, some fixed and some adjustable. 73's,,,,,,,,Joel   KB0FPT
On 10/24/2014 9:48 AM, Kenneth G. Gordon wrote:
> 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
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