[ARC5] Selectivity and the BC-455

[Ian Wilson]

Just watched the video, very nice.

For once, the crystal spreadsheet and the parts drawers corresponded,
and I have a 2833.75kHz crystal. I also have a 7277, which is a 2830kc
1st IFT. It has 2 windings.

The IFT appears to have been modified already, which is good news
for this project. The crystal I have is an HC6/U, which might just fit in
the IFT can but it looks tricky.

Since the IFT has been modified already, I am thinking of going a
step further and replacing the existing coil with something on a toroidal
core.

73, ian K3IMW


On Fri, Oct 24, 2014 at 8:48 AM, Kenneth G. Gordon <kgordon2006 at frontier.com
> 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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