Joerg said:
Hello Patrick,
Agree, but at least this Loewe radio had a BW selection at all. It did
help some, especially on shortwave.
And on short wave the selectivity is very high since the IF coils are
kept apart, so high selectivity is easy, although you have a higher insertion loss,
and need more gain.
The AF bw on short wave reception is usually quite poor.
adding R across such LC transfromers merely lowers the Q,
but does not take advantage of the flat topped pass band character as one brings the coils
of the IFT closer together, but not too close, lest
one get a double tuned peak, which occurs
when LC coils are over coupled in a tuned IFT.
It is a bit better in the US since we have so many different ethnic
groups. Occasionally you can catch interesting music on AM, especially
from countries that otherwise only run propaganda stuff on SW. Once
emigrated the people then are free of those bounds and can share their
real cultural heritage.
I tire quickly of the ethnic stations. Mostly talk and babble in a foriegn lingo
between the occasional bit of music, and none of it as nice as something
written by Bethoven or Mozart.
I don't even like a digeridoo; sounds like a washing machine with a problem.
Stepan Grappelly is almost as bad on jazz violin.....
Way to go. I never understood why AGC in "contemporary" radios doesn't
regulate the first amp first.
Noise reasons, cost reasons....
In my own RF designs I usually even go
before the first stage using a PIN diode attenuator. That way you don't
have to be running up and down the linear range. Of course, in a
consumer device the extra Dollar for the PIN section wouldn't be in the
cards.
When I compare the Astor BPJ of 1959 with the Philips Gamma of similar
vintage there isn't much difference if you discount the parts the
Philips contains for FM and band switching. Performance is similar, too.
The Astor is a tad better in AM reception, probably because it has a
much larger ferrite rod.
But ferrite rods have a high Q, and enough to cause side band limiting,
and hence AF bw limiting, even without the IFTs.
The set needs to track well with ferrite RF input LC.
But the ferrite picks up the magnetic RF rather than the electostatic,
and gives less hum.
My set with a long wire antenna and dual
input LC circuit hums real badly right on 846 kHz which is the Radio National station,
and its because of some really bad source of local interference, presumably
coming in on the mains wiring.
I have a second set with a ferrite rod mounted above the one I normally use
for times when whoever is causing the interference has their
interfering gear turned on.
Sometimes I hear when they switch on.
The Philips wins in versatility because it has
more taps on the power transformer so I could easily swing it to 120V.
The Astor only offers a 200V tap so it needs to run off the 230V rail
which I only have upstairs.
The Philips also boasts the better enclosure, nicely polished wood. Then
again, the Astor is much more compact and portable.
I have a post-WW2 radio where a true minimalist approach had been
attempted. It is a Jotha Liliput. Plastic case, pretty shoddy
construction for my taste. I got it to run again but the performance,
well, leaves a lot to be desired. It is a regenerative single tube set.
Yuk.
Patrick Turner.