[ARC5] Selectivity and the BC-455

[Ian Wilson]

To be clear, this IFT has 2 windings but only one is tuned.

73, ian K3IMW


On Fri, Oct 24, 2014 at 9:42 AM, Ian Wilson <ianmwilson73 at gmail.com> wrote:

> 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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>
>