[ARC5] BC-453 (or R-23) in AM reception.

[Kenneth G. Gordon]

On 12 Jan 2014 at 16:34, Leslie Smith wrote:

>   Hi list-readers,
>   Suppose a converter is used ahead of a navigation set such as an
>   BC-453 so that the set is used to listed to an AM broadcast station.
>   Given that the station of interest has mostly spoken content and
>   little music, will the narrow band-width allow some sort of
>   reasonable reception?

Yes, of course. The passband of the BC-453, even when the IFs are set to 
their "narrow" condition, is not a "square" shape factor, but is more "rounded 
triangle" shape. Minimum (maximum?) selectivity at the -3db (2X down) 
points is on the order of 1.1 KHz when the IFs are set to their narrowest 
condition, and around 3 KHz when at their widest. 

At the -60 db (1000X down) point, the selectivity is 4.5 KHz, according to the 
U.S. Navy maintenance manual on the ARC-5. Again, this is with the IFs set 
to their narrowest condition.

Neither of these precludes listening to music, although it is certainly not 
"hi-fi".

> Would the narrow frequency response make
>   reception simply too "military communication quality" to endure?

Not at all.

>   I'm aware that the core of the IF transformers can be pushed "in" to
>   give a broader IF response.

In fact, you can push one, or two, in, while leaving one, or two, out to vary 
the shape of the passband somewhat, flattening the peak, etc.

If you have set up and used that "visual alignment" method using a swept 
signal generator, you can very easily see the effect of adjusting those rods.

>   Has any-one here used a BC-453 or R-23 to listen to the BC band in
>   this way? I'm particularly interested in that point.

Yes. I have. Although, as I have said, it somewhat restricts the audio 
passband, it is certainly not unpleasant to listen to, even for extended 
periods.

Remember, the selectivity obtained is due to LC filters, not mechanical or 
crystal types, therefore the passband shape is much more "rounded" than 
either of the other two. Skirt selectivity is not anywhere near as good as the 
other two types of filters, although it certainly is "impressive" for LC filters.

I suspect you are worrying too much about something that is easily dealt 
with.

Give it a try and see what you get.

I used to use my RAL-7 to listen to shortwave BC and despite its very narrow 
AUDIO passband, it was still not unpleasant, although it most certainly was 
"restricted".

vy 73,

Ken W7EKB