Lostgallifreyan wrote:
Lostgallifreyan wrote in
:

Jeff wrote in
:

Lostgallifreyan wrote:
Jeff wrote in
:

It seems very strange that you are taking things to the ultimate when
considering coax cable, whilst considering using a very inferior
portable radio for your reception!!

Not really. A few tens of metres of cable whose cost is not more than
3 times the cheapest of satellite coaxes, and whose total cost is less
than half the lowest cost of that radio when found second-hand, is
hardly overdoing it.
I think the point is that radio is very much under-doing it!!!

Why are you so set against that radio? A lot of people like it (some of
them enough to modify it rather than replace it). What do you recommend?
And how much would it cost? This thread wasn't about that radio but this
is worth pursuing, you seem to have a strong feeling about it. I just
bought it because it seemed like a good cheap base to start from. (Not
cheap if I'd had to buy new, but I purposely avoided that).


Further, the ATS-909 is a fairly old design. Not many appear used on eBay,
and new ones still sell for what I think are excessive prices, from Germany,
Japan and elsewhere. Bad radios surely get sold on as fast as people can
pass them off on someone else. They're unlikely to be in shorter supply
secondhand than new, when they're as old a design as this one is, and very
few second-hand ones remain unsold when an auction ends. I'm not trying to
correlate buyers opinions with the finer points of radio engineering, but it
remains a fact that people would rather keep them and use them than sell them
on,

OR throw them away when they die, or put them is a box in a closet. You
really don't know.


which is fairly convincing as an argument to get one if the price is
good, so I got one. Had to wait a few months too, for an auction that had low
competition, but I think it was worth it. A lot of people documented
modifications, suggesting an enthusiastic technically adept following.

That technically adept following could not provide any useful
information on the input impedance. While actually knowing the impedance
may not be of much value in your endeavors, given the availability of
the schematic, someone could have modeled the input in Spice.


That
is one of the things that helped me decide to get one. It means I'm not
reliant on one supplier for info or advice if I need to fix or modify it.

Really poor radios don't go through what I just described, they sink without
trace instead of surviving for over a decade with such deep involvement from
so many of their users.

A really good radio probably doesn't need a bunch of modifications to
deal with deficiencies.

Some radios hang around because they were built in large volumes.
Quality and performance may mean little.

The point that was made is your radio does not really warrant the effort
your are putting into the antenna. Any variety of quick and easy
antennas may give you adequate results.

So, here is what I see.
1) Worrying about the radio's input impedance is of little value
2) The choice of coax won't make much difference - performance wise, but
copper braid is much easier to solder to.
3) A simple wire antenna at the end of the coax should be sufficient
4) A balun (or un-un for the picky) between the antenna and coax is
probably worthwhile. 9:1 or 10:1 won't make any difference.
5) Figure out what you are going to do about lightning protection.
6) Rather than spend weeks sorting out the details, string up some wire
and listen to the radio.