Alex wrote:
>
> "Patrick Turner" <info@[EMAIL PROTECTED]
> wrote in message
> news:481C9439.C908EF3A@[EMAIL PROTECTED]
> >
> >
> > Alex wrote:
> > >
> > > "Patrick Turner" <info@[EMAIL PROTECTED]
> wrote in message
> > > news:481B4967.C86278B8@[EMAIL PROTECTED]
> > >
> > > > I repair, rewire, or seriously modify at least 5 AM radios per
year.
> > > > I've done 3 this year and there are 3 waiting to be done, and its
only
> > > > May.
> > > >
> > > > I built a complete radio in 1999, 10kHz of AF bandwidth, variable
> > > > selectivity, linear IF amp, linear detector, linear AF amp with
> > > > EL34 in triode with 12AX7 and 12dB FB. Rola 12" Deluxe speaker
from
> 1953
> > > > with a dome tweeter from 1972, because the 12" speaker is fairly
flat
> to
> > > > 5kHz.
> > > >
> > > > I have never heard any other AM sets that come close except
> > > > the one in the AM-FM tuner at my website, which I designed, and of
> > > > course the
> > > > Quad AM tuner all tubed, that isn't bad at all.
> > >
> > > Could you please give a link to your website? Is there a schematic
of
> that
> > > radio, mentioned above, which you designed? Is it TRF?
> > > Regards,
> > > Alex
> > >
> > > > Patrick Turner.
> >
> > The kitchen radio I mentioned from 1999 above
> > has a different circuit to one I just gave you at
> > http://www.turneraudio.com.au/am-fm-radio-tuner-multiplex-decoder.html
> >
> > I don't have the kitchen radio schematic at the website.
> >
> > But what my kitchen radio does have is..
> >
> > 3 gang tuning cap.
> >
> > Two RF coils with ferrite cores for high Q and two C gangs are coupled
> > so that there is no sideband cutting of AF
> > right across the AM band, which means each coil is tuned to a slightly
> > different F.
> >
> > There is no ferrite antenna, just loose coupling from a wire antenna
to
> > one input coil.
> >
> > There is a variable µ twin triode used as a cascode RF amp stage and
RC
> > coupled to the 6AN7 F converter
> > to make an IF signal.
> > There is AVC voltage applied only to the cascode input triodes.
> >
> > The IF amp is 6BX6 with unbypassed Rk and no AVC applied, so its
fairly
> > linear.
> > There is a cathode follower and diode detector cabable of detecting
> > about 10 times the actual voltage detected with very good linearity
and
> > bandwidth.
> >
> > Two standard IF trannies are used, but the first one after the F
> > converter
> > has one IF coil monted on a slide and a knob on the front of the radio
> > rotates to move the coil to coilo distance about 10mm.
> > This allows the radio to be tuned normally to a single
> > a single peak when tuning and then after closing the coils closer, the
> > IF BW is much increased to allow 9Khz of audio to be detected, but all
> > while
> > retaining very good skirt selectivity and rejection of
> > stations only 45kHz away even if they have 20 times the transmitting
> > power.
> >
> > There are in fact 6 tuned circuits in all, so the attenutation
> > of signals away from the wanted stations is excellent,
> > yet what is wanted sounds very nearly as good as FM.
> >
> > The 3rd gang of the cap is for the oscillator.
> >
> > I paid very careful attention to tracking.
> >
> > TRF sets are quite poor performers today because the stations are now
> > close together,
> > unlike in 1935, when the band wasn't crowded.
> >
> > TRF usually used only 3 tuned circuits which needed careful tuning,
> > and they gave a peaked response, not a flat topped band band pass
> > character of a critically coupled IFT.
> >
> > The Superhet with IFTs is definately The Best hi-fi AM tuner you can
> > have if its built right,
> > and 99% were atrocious, and all mainly conformed to the lowest common
> > denominator of utter crap.
> >
> > When Radio was king before TV, there were very many makers all vying
for
> > a market share.
> > They all agreed with each other to ensure the standards were lousy.
> >
> > Patrick Turner.
>
> May I ask you, Partick, which AM radio station has the least distortion?
I
> live in Sydney, and I wold say, BBC (around 600KHz) is the best.
The BBC does not broadcast at 600kHz into Sydney areas.
I think you mean 2FC, or 2BL. One is used for Radio National.
Networked RN is on FM elsewhere in Oz.
A Google search would tell you a lot more.
I RN at Canberra at 2CY, 846kHz, and music programmes sound very well
indeed.
Audiophile quality.
Never mind the compression and MP3 formats.
2CA at 1053 here does ancient pop music and adverts, so I never listen
to it
but the processing used on the old music source material makes it sound
better
than in 1970. The gear is simply better and the digital compressing
removes clutter in the audio and it sounds cleaner, but I don't wanna
hear
'House of the rising sun' another 400 times each month.
> Others use
> some elaborate compression and clipping which makes one's ears tired
very
> soon.
I find the opposite is true.
Its the intellectual content or lack of it that prevents me listening
or watching most broadcast media including TV and FM.
I don't have a working TV in my house because its a corrupting
influence.
>
> Do the stations INDEED transmit 18KHz of bandwidth? With only 9KHz grid?
In the ACT, the closest any two stations are is 1008, racing info junk,
and 1053, old mouldy pop and advert junk.
Both these stations are only 5km away from me with 1053 at 5kW,
and 1008 at 300W.
Only 45kHz apart. A good AM set will pull in 1008 without hearing 1053
feintly in the background. Many AM sets fail the test miserably,
including SS junk.
A good set would allow 15kHz of AF modulation on the carrier, ie
sidebands extending 15kHz each side of the carrier.
There is another station on 1008, in Tassie, but see the list of
stations in Oz and their F.
AFAIK, where full AF BW up to 9kHz does not cause interference to other
stations, it is allowed.
Find out with Google.
>
> On the stereo-decoder note, what is the phasing of 19KHz pilot with
respect
> to the 38KHz (suppressed) carrier: do the zero-crossings coinside (every
> second one) or peaks coinside (every secon ones)?
I have never bothered to check.
The decoder just works.
It took lots of fiddling around though.
>
> I would guess, the peaks. That way it would have been easier to derive
38KHz
> simply by a class C frequency multiplier.
>
> By the way, in the Russian stereo system, there is no 19KHz pilot, but
just
> a 38KHz vestige with a proper phase. It gets boosted by a q-multiplied
LC
> tank and fed to a diode ring, similar to what you did..
Yeah, you could have 38kHz, not totally suppressed, instead of the
19kHz which is 10% of the maximum AF signal,
so to prevent IMD between upper AF and 19kHz, the AF used to modulate
the
carrier must be cut off sharplyat 16kHz.
Maybe the russian system works better.
But of course the 38kHz is too low, and should be 50kHz, and then the
pilot could be at 25kHz, and that would make receivers easier.
But the GE-Zenith system allows for multiplexing and there can be
complete audio channels with 67kHz and 96kHz sub carriers.
Patrick Turner.
>
> Regards,
> Alex
|
