I picked up this unit about a week ago. It was ok when receiving stations,
but on interstation noise with the preselector untuned, gain was low. The
clue to the problem was that with AGC disabled and the RF gain control
turned all the way up, the radio had higher gain than with the AGC enabled.
The problem was adjustment of R507. This adjustment had probably drifted
with component ageing over the years. It appears to set the knee point of
the AGC. Once adjusted, the radio has the same gain in both AGC and MGC
modes. I think it is the best of the German / Portugese Grundig models that
I have seen. Not only does it use dual-gate MOSFETs for all of the ranges,
but it also uses separate ceramic ladder filters for upper and lower
sideband reception.
Somebody must have pulled out all of the stops when they designed this
receiver.
The only negative point I noticed was some excess sideband noise from the
synthesizer. If you tune near a very strong station, you will hear the noise
floor rise up when you get within a few kHz of the station. Also, on 49M in
the evening you can hear a higher noise floor.
One of these days, I will narrowband the PLL's loop filter up a bit. Not a
bad design...........this one's a keeper!

Pete

Thanks for sharing this information , very interesting!

Greetings,
Knut Otterbeck

"Pete KE9OA" skrev i melding
...
I picked up this unit about a week ago. It was ok when receiving stations,
but on interstation noise with the preselector untuned, gain was low. The
clue to the problem was that with AGC disabled and the RF gain control
turned all the way up, the radio had higher gain than with the AGC enabled.
The problem was adjustment of R507. This adjustment had probably drifted
with component ageing over the years. It appears to set the knee point of
the AGC. Once adjusted, the radio has the same gain in both AGC and MGC
modes. I think it is the best of the German / Portugese Grundig models
that I have seen. Not only does it use dual-gate MOSFETs for all of the
ranges, but it also uses separate ceramic ladder filters for upper and
lower sideband reception.
Somebody must have pulled out all of the stops when they designed this
receiver.
The only negative point I noticed was some excess sideband noise from the
synthesizer. If you tune near a very strong station, you will hear the
noise floor rise up when you get within a few kHz of the station. Also, on
49M in the evening you can hear a higher noise floor.
One of these days, I will narrowband the PLL's loop filter up a bit. Not a
bad design...........this one's a keeper!

Pete

Anytime! I like your website.........very informative about those Grundig
radios.

Pete

"Knut Otterbeck" wrote in message
news:sezyf.3759$zc1.2259@amstwist00...

Thanks for sharing this information , very interesting!

Greetings,
Knut Otterbeck

"Pete KE9OA" skrev i melding
...
I picked up this unit about a week ago. It was ok when receiving stations,
but on interstation noise with the preselector untuned, gain was low. The
clue to the problem was that with AGC disabled and the RF gain control
turned all the way up, the radio had higher gain than with the AGC
enabled.
The problem was adjustment of R507. This adjustment had probably drifted
with component ageing over the years. It appears to set the knee point of
the AGC. Once adjusted, the radio has the same gain in both AGC and MGC
modes. I think it is the best of the German / Portugese Grundig models
that I have seen. Not only does it use dual-gate MOSFETs for all of the
ranges, but it also uses separate ceramic ladder filters for upper and
lower sideband reception.
Somebody must have pulled out all of the stops when they designed this
receiver.
The only negative point I noticed was some excess sideband noise from the
synthesizer. If you tune near a very strong station, you will hear the
noise floor rise up when you get within a few kHz of the station. Also,
on 49M in the evening you can hear a higher noise floor.
One of these days, I will narrowband the PLL's loop filter up a bit. Not
a bad design...........this one's a keeper!

Pete