schrieb:

The designer(also the main engineer of DE1103 & Grundig SAT800) now ask
advise of the receiver function from BCLer, the DE1108 will be the
high-end receiver of DE 110X series, it comes with a large dot matrix
LCD display(128*64) two way speaker system, MP3 recorder, AM sync
detector, SSB, dual conversion, the reference basis is SAT700, it
should has better performance than sony 2001D, 7600G, SW77 even SAT700,
the outline dimensions will be large than SAT700,pls post your thougts
here, I will take the message to the design, thank you!

Some points I can think of offhand:
* Use good quality IF filters, i.e. 6-element ceramics or such for AM.
(If these should not be available, get inventive.) I'd combine these
with a wider tail filter. I guess DSP usage is not an option? Some
care when applying the 1st IF crystal filters may not hurt, to ensure
good image rejection (as well as intermodulation characteristics). FM
should use 3 cascaded filters with a medium bandwidth to match the
Satellit 700, with 3 gangs (tuned front-end circuits) recommended.
* With a two way speaker system, make sure sound is as good as possible
with the concept, and that not only to Chinese ears. Audio engineering
has sadly been frequently neglected in the last 10...15 years or so.
If some kind of EQ circuit (for speaker operation only) is needed, so
be it, the radio makers of yore also used such tricks. (There should
be an additional tone control, tastes in sound differ after all.) Some
research in terms of vibration suppression or loudspeaker building in
general and such may be of help. Given the sound is right, a simple
line-level 3.5 mm (stereo) input for amplifying purposes might be a
nice touch.
* Get the internal shielding right, particularly with a non-negligible
digital section.
* Oscillator pulling by lighting LEDs (DE1102 in SSB) and other such
funky stuff better be ironed out, along with operating kinks. Plain
ol' analog volume control and paged decimal presets please.
* Front end selectivity for the AM ranges should be one filter for LW,
one for MW and then several (~ octave) for shortwave, maybe further
varactor-tuned. (The '700 had an electronically tuned preselector,
though it seems alignment of the thing from the factory wasn't always
that great.) Those living near MW transmitters (rather common in the
US) are likely to appreciate a highpass filter for shortwave.
* A big receiver should offer sufficient space for a big ferrite rod
antenna, for good LW/MW (and I'd also suggest low SW up to ~2.5 MHz or
so, where telescopic antennas tend to be inefficient) sensitivity and
directionality. Something rotatable à la RF-2200 might be worth
considering; the bigger a receiver is, the more tiresome rotating the
whole thing becomes.
* I suggest at least two different frequency steps, better 3 - usual
frequency grid for the band, 1 kHz and then something smallish (maybe
100 Hz plus analog fine tuning, or = 20 Hz without).
* Memory presets: With EEPROMs being rather inexpensive these days, a
few hundreds with at least 8-digit name tags should be possible. But
if MP3 recorder functionality (with commodity flash memory, I guess?)
is already present, one could also use the associated storage. If this
should be removable, a simple file format like CSV could enable easy
presets interchanging and PC based updating. (This might even include
firmware updates, which certainly are not a bad idea.) The MP3
recording probably features adjustable sample rates, (average /
variable, not only constant) bit rates and mono/stereo selection?
(Shortwave recordings would probably require no more than 11025 Hz
mono and thus a relatively low data rate, while FM stereo would best
be recorded with 32000 Hz or 44100 Hz in stereo.)
* In spite of all possible complexity, the essential functions - tuning
and frequency entering, tone control, basic preset saving and
recalling - must remain simple and intuitive to use. If someone can
figure these out without reading the manual, this is good. On a bigger
set, placement of things like a tuning wheel requires some thought in
order to avoid (arm related) fatigue during longer listening sessions.
* Any plans for DRM reception? (Provided some matching and not so power
hungry ICs are already available. If not, a 12 kHz IF output derived
from a suitable spot - maybe behind a 10...12 kHz filter normally
improving ultimate rejection - is better than nothing. Reserving some
space for an add-on DRM board may not hurt then.) What about RDS for
FM?
* Dual balanced 1st mixers have been very similar in portables, and
that for over 20 years now - how boring. Try some other circuit
variants, maybe these give better results.
* For a receiver of this class, availability of servicing instructions
is virtually a must.

I'm pretty sure build quality will not be an issue, given I see little
reason to complain about this even on the little DE105 (I recently
obtained a relabeled one). DEGEN certainly has the potential to become a
major player in the mobile entertainment market.

Stephan
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