[ARC5] More BC-455 IF thoughts

[Bill Cromwell]

Hi J,

What you are describing is "stagger tuning". Another list member already 
alluded to that. The trouble David (the OP) told us about is an IF 
transformer on a completely different (far removed) frequency.

The show-offs among us use a spectrum analyzer and tracking generator to 
align IF stages (basically filters) but we can get it done with more 
basic gear like something called a wobbulator. I am sure if I had a 
spectrum analyzer and tracking generator I would be pleased to use it:) 
Use those kind of tools to dial in your passband whether you want it 
wider or narrower. My last wobbulator died a long time ago. I need to 
get another one up and running.

You might try connecting the signal from your last detector (audio) to 
your computer sound card and run something like Spectran or fldigi. If 
you pay attention you can see the overall shape of your receiver's 
passband on the waterfall or spectrum display. Just a lil hint. Even you 
shun using such 'on the air' you might benefit from using those digi 
gizmos  on your work bench.

73,

Bill  KU8H

On 04/13/2018 11:13 PM, J Mcvey wrote:
> Traditionally, yes, the term 'stagger tuning' refers to widening.  That
> is accomplished by having the peaks at the high and low of the BW freqs,
> WHen one end is decreasing the other is increasing.
>
> Pehaps I shouldn't have used the term  "stagger tuning".  What I propose
> is consecutive "detuning", but within the -3 db area of the LSB,. Only
> 1/2 of the BW of the next stage would be useful because it will see a
> very attenuated signal at the lower end from the previous stage.
> The coil BW is the same, but the input at low end won't be there
> because  it's deep on the skirt of the previous stage, maybe -12 db or
> more.There will be little signal to amplify on the lower freq end of the
> second stage. ( nothing in-nothing out)
>
> If you draw the "humps" on a piece of paper, with the second peak just
> left of the first, the upper sideband is attenuated, The  3rd If would
> "see" even more narrow swatch... I think...maybe not?
>
> I hope this is a better description . what say you?
>
>
>
> On Friday, April 13, 2018, 10:40:33 PM EDT, Bill Cromwell
> <wrcromwell at gmail.com> wrote:
>
>
> Hi J,
>
> Stagger tuning is used to increase bandwidth - just the opposite of
> narrowing it.
>
> 73,
>
> Bill  KU8H
>
> On 04/13/2018 10:15 PM, J Mcvey via ARC5 wrote:
>> Well , the BC-455 that I THOUGHT had all three IFs changed to 85Khz
>> wasn't that .
>> The 1'st IF numbers were faded so I ASS-u-med that they were all the
>> same. Unfortunaely, only the 2nd and 3rd IF were 85Khz , The ist IF
>> tuned out to be the original, thus all of the heavy mods were about a
>> second oscillator which he must have removed the Xtal or whatever, as
>> there was no sign of a secondary osc circuit coil either.
>>
>> Anyway, I was wondering if stagger tunning the IFs might be a way to
>> narrow the BW on the cheap?
>> For instance 1st IF tuned at 2830 , 2nd tuned in the LSB of the first IF
>> and the 3rd IF tuned in the LSB of the 2nd.
>> AM might sound funky, but LSB and CW should be a lot more selective, no?
>>
>>
>>
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> --
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>
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