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Synchronous AM on the RA6790

 

Hi everyone,
?
I have a question for the technical guru's.
?
When I tune in AM stations using SAM on my WJ8711, its quite obvious that is generating and reinserting its own carrier. There is a momentary heterodyne if the AM signal changes in frequency suddenly while it adjusts to the correct frequency.
?
The RA6790, while it performs fabulously well as an AM receiver, does not show any evidence of this happening at all. It also doesn't perform as well as the WJ on selective fading. Why then is it widely believed that it has full time synchronous AM?
?
Cheers,
Peter - VK2AN
 

Hi guys:
Not a technical guy, however the 6790GM here is not improved by the addition of the Sherwood SE-3.
That says something
I do use it anyways however, because the audio out is strong enough to drive bookshelf speakers.
Incidentally, the SE-3 with the Racal ra6217E is a revelation.

Dan from Saskatchewan.


On Fri., Feb. 28, 2025, 3:16 p.m. Peter E via , <elekessy=[email protected]> wrote:
Hi everyone,
?
I have a question for the technical guru's.
?
When I tune in AM stations using SAM on my WJ8711, its quite obvious that is generating and reinserting its own carrier. There is a momentary heterodyne if the AM signal changes in frequency suddenly while it adjusts to the correct frequency.
?
The RA6790, while it performs fabulously well as an AM receiver, does not show any evidence of this happening at all. It also doesn't perform as well as the WJ on selective fading. Why then is it widely believed that it has full time synchronous AM?
?
Cheers,
Peter - VK2AN
 

On Fri, Feb 28, 2025 at 09:16 PM, Peter E wrote:
does not show any evidence of this happening
That's simply? because there is no phase locked carrier insertion oscillator in Am mode? , the detector carrier is derived from the clipped off-air signal. if the carrier fades out, then Thers nothing to re-inject , as the? tune passes over the signal, the carrier / side band relationship ,remains unaffected.?
?
The RA1771&2 , 1778 have carrier locked AFC , again if the carrier drops then the? Afc holds the? last good lock frequency?
the afc enters at the? 34 M osc to alter set tune, not linked to the? detector[s]?
?
This and ssb/isb enables better recovery of? AM , but, thats using the? internal phase locked CIO and the? filters to
present the? detector with usb/lsb signal ,?
?
Anything on from this, need to add DSP , something like RTL dongle in direct sample mode and sdr-sharp or other ,
looking at the 455K IF out [or 1.4 MHz ra 1778] , various 'locked'? detector modes are then available ...?
?
73 Graham
g0nbd?
?
?
?

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