#Satellite Weather
7 messages in this thread
Your HQ-160 can "do" fax. Frequency stability affects the image as follows:
if the radio drifts, the grey levels will shift. In the case of a simple
interface, (a 16 level one, likely in the case of the amiga) your reciever
would have to drift 50hz in order to shift the image by ONE grey level –
which you CAN see, but isn't what I'd call objectionable. 100hz, 2 grey
levels – and so on.
Further, this drift has to occur over the duration of the fax signal; in
other words, if you hq160 has a drift of 50hz/hour, (unlikely, once warmed
up) then over the time it takes to send six images, you will drift by one
grey level. So as you see, it won't be a problem.
In my msg to you, I mentioned freuency _accuracy_, not stability – only so
that you would be aware that the value your DIAL reads might not be
_exactly_ 8078 khz when you are tuned correctly as the frequency that your
dial reads may be slightly off (and that's all it takes.
The first satillite image you see, you'll be able to tune properly – they
send grey scales more often than not, and you just tweak the dial until all
the grey levels are in the scale where they belong.
Be patient a few weeks, John… I have something coming for the Amiga that
will blow you away – it's a ten chip construction project, and among other
things, your Amiga will do those wefax images in such a manner as to blow
you away.
Either data files (Schematic and PCB) will be posted here, or we will be
going commercial (likely) with it and you'll be able to purchase the
hardware or a kit or something.
We are talking full color SSTV, b&w sstv, wefax, and satfax here.
Is there a simple, inexpensive receiver (or approach) for non-ham Amiga owners
who still might want to experiment with picking up such fax transmissions using
your interface?
Rick
There will be; Right now, I'm not done – it will be a few weeks before I
get things working the way I want them. Once done, however, all you need is
a communications reciever with sideband capability – even a "bfo" might be
ok, as long as it is fairly stable and not prone to overloading. With that,
you connect the reciever's audio output to the input of this interface, run
the program, and you'll have FAX images, no problem.
For HAM operation, you can additionally connect one of the audio channels
to your microphone, and you have FAX output and SSTV as well – of course,
it will recieve SSTV, and you don't need to be a HAM to do that either.
Finally, both SSTV and FAX are legal (and work very well) over the
telephone line.
Mmm. I have an old Heath Mohican that my dad built. It was a fine
receiver in its day — for what it was — but it was never very stable, and
it's gotten worse with age, so I don't expect that would work. Maybe I can
find a friend with one that I can get interested in the project. (Hah…
as if I had time, what with trying to get ready for WOC!)
Well, you can always try it first, neh?
Ben,
Thanks again. I will wait. Commercial sounds good to me. Its hard to
beat economies of scale. Only advantage to brewing your own is to build the
unavailable or self satisfaction.
The HQ-160 is only spec'd for less than 100Hz drift. Lately, even when
it is warm, I have noticed up to 1000 hz drift. After several hours though, it
is more stable. I'll have to drag it to work or borrow some test equipment. I
have noticed that the first half of the first IF stage tends to drift out of
alignment. The others are quite stable. I don't know if that would cause the
frequency drift though. It certainly affects the sensitivity.
Any guesses from your experience?
Yes – depending on the local oscillator configuration, you may be
experiencing several things. warmup, of course, does not count; tubes
change physical size during that time, and all bets are off. If your
oscillator is unbuffered, then the coupling capacitor to the mixer stage(s)
could be varying in value, such that the load on the oscillator is
"pulling" it. capacitors at ANY place in the oscillator itself are suspect;
screen decoupling, emittor bypass, anything in a tank circuit (like those
usesd to "pad" the variable capacitor)… check any coils (for that band)
for "baked" (and therefor flaking) insulation – a turn cutting in and out
can 'pop' you up and down a small amount as it varies the inductance of the
coil.
Clean ALL the dust out of it – dust can make a reciever do ANYTHING. You
should do that before you even TRY do diagnose it. Likewise lubricate the
capacitor bearings and use contack cleaner on all the switches that change
the bands. Same basic kind of reasons – dirt gets in there, you end up with
a series resistance (that varies with the square of murphy's law) that
upsets the Q and operating frequency of the oscillator. New tubes may be
called for, and if so, either the oscillator, the mixer, or the last
(only?) front end stage may need it, or any combination.
If there are covers on the tubes (little metal shields) make sure that you
use the tuner cleaner on the base area where they attach to the chassis;
they are supposed to provide a shield for the tube, but if the connection
to the chassis is bad, they can provide a varying capacitance to the tube
elements, which is a bad deal. I could go on, but these are the things that
I do when I rejuve an old radio – and I (so far, crossing fingers) always
get then stable and happy. Just did one that was given to me in Montana…
thing works great now.