Kate Fights said:
Thanks for all the replies re: valve vs solid state radios
There was some very interesting reading and I learnt
quite a lot in that thread.
I have another question
I mentioned one of the radios I had was a transistorized
table radio. Well this also is a portable radio in that
it can be run via D size batteries.
Question is how far a signal have you ever received on a
portable AM band radio. Some nights, especially in the
colder weather for some reason I can get stations like
2DU in Dubbo on the radio. Can't explain why it works
more in the colder weather but it does. And the station
comes in well enough that you can hear it over all the
background noise.
This too considering I am in SA in Adelaide.
So with that in mind how far has anyone picked up a
radio station.
We had 2XX here in Canberra on 1,008 kHz, same as 2AD in Tasmania,
and that could be heard in the background sometimes, since 2XX
was only 300 watts. Now they have moved to FM, and a sport station
with races is there, with zero fidelity, offering odds on chances of
losing all yer dough.
I have often heard Queensland stations here, and it depends on
ionosphere refelections etc, and I am at a loss to
explainn further, but should you be able to erect a long enough antenna
with a length ideal for the broadcast band, preferably with an L plan
shape,
then the two antenna signals can be phase adjusted to prefer the station
you want.
It won't be hi-fi.
But the trouble is most stations are same old boring stuff you get from
the city stations since they
have networked them all.
For short wave, a rotating beam antenna like what the ham radio guys use
is quite good but
their beams favour 7, 14, 28, 56 MHz.
So maybe you shouls tudy the old books about radio wave propagation and
antennas; many books are devoted just to antennas.
If you have a non resonant long wire antenna just thrown over the roof
and running in through a window to your set,
then its wise to make a good earth for the set, since the antenna signal
needs a *circuit*, so electrons can move from antenna to ground and back
One can also use an inductor to earth, then a series tuning capacitor to
the antenna,
and take the radio signal from the inductor. The capacitor is then tuned
so the antenna
and cap and inductor make a resonant circuit and this often boosts the
signal you want
with others close by maybe 15 dB. Noise outside this band will be
rejected.
MW and SW depends a lot on antennas. Ask any ham.
I have to help a ham operator lower one antenna and raise another
tomorrow.
The beam we are taking down has 4 rods or 9 metres long each, quite a
beast.
Radio interest was real big in the 1950s, when
guys built all their own gear.
Now they buy at DSE and plug and play,
or they use a "virtual" receiver that appears on a PC screen
so the maouse can be used to alter RF gain noise filtering, selectivity,
band filtering, side band, et all.
This approach simply digitisers the RF input signal and
counts what comes in, then a program is applied to decode the data.
The radio waves are still there but today's latest receivers are very
different to what they were
up to the age of the PC.
Still, I have several old 7 tube communications sets I'd like to restore
that an old ham left to me when he passed away a few years back..
They would have gone to the tip otherwise.
They can still give pretty good performance, and its possible to add
digital processing to clean up speach signals.
Nothing here may be of much interest to hi-fi folks but the old ham I
knew
was very interested in the lo-fi side of ham and talking to old mates in
the UK
as well as what he could get from his sound system.
To know more about radio, you have to read books and do experiments.
Patrick Turner
