Re: News : ARM Trying to Buy AmperComputing

On 2025-01-31, The Natural Philosopher <tnp@invalid.invalid> wrote:

On 31/01/2025 04:49, Robert Riches wrote:
>

Regarding the (theoretical) audio bandwidth of US AM broadcast
radio:
 
     https://en.wikipedia.org/wiki/AM_broadcasting
 

Well, you live and learn
>
Absolutely not the case in Europe
>

In the section titled "Technical information" around 80% of the
way down the article, the audio bandwidth was reduced in 1989 to
10.2kHz.  Prior to that, it was 15kHz.
 
The 15kHz matches my memories from earlier studies and the manual
that came with the Pioneer TX-7800 tuner I bought in 1980-81.
That tuner has a front-panel switch for AM IF bandwidth that
yields ~5kHz vs. ~15kHz audio bandwidth, based on some filters
(ceramic, IIRC) that were pretty high tech for the time.  Sadly,
it seems some dust has become lodged in the mechanical tuning
capacitor.  It still has partial function but like when it was
young.
 

Yup, You would need switchable IF strips or tuning parts for that

The full schematic was included in the literature that came with
the tuner, and it's on the desk in front of me.  (Didn't even
need to buy a Sams folder to get the schematic.)

If I'm reading the schematic correctly, the AM RF and IF is done
by Q16, a 16-pin HA1197 that contains an RF Amp, a mixer, two IF
amps, a detector, and an AGC amp.  There are two RF/IF
transformers, one attached to the mixer block and one between IF
Amp 1 and IF Amp 2.

From the mixer, the IF signal goes through a wide-bandwidth
ceramic filter labeled F6, a transistor amplifier, a second
transistor amplifier, and a narrow-bandwidth ceramic filter
labeled F7.  There are two diodes feeding into IF amp 1, one
coming from the collector of the first transistor amplifier and
one coming from the output of F7.

The front-panel AM bandwidth switch connects to points among
those two transistor amplifiers and F7.  It looks like each of
the transistor amplifiers makes up for signal loss in each of the
ceramic filters.

tl;dr: It appears the diodes switch either the wide-bandwidth
signal or the narrow-bandwidth signal into the input of IF amp 1.
In other words, the signal conditionally bypasses the
narrow-bandwidth filter.

--
Robert Riches
spamtrap42@jacob21819.net
(Yes, that is one of my email addresses.)