Cable Shielding Misunderstandings
 

Jeff wrote in :

It is a perfectly adequate radio for what it was designed to be; a
portable that you take away on holiday to listen to BBC world service
on, but as for using it for anything more it is lacking.


Lacking what, specifically? I wanted a general purpose radio with full AM
coverage to 30 MHz, and I wanted it to be cheap and portable. Then I wanted
to give it a decent chance of getting signals when I'm not carrying it
around.

As for a radio that that is only fit for getting BBC World Service, are you
sure you're not confusing the ATS-909 with whatever Sangean's original was,
as cloned by Roberts with model R9921? That really IS a basic radio designed
for that purpose, the ATS-909 does more.

Even you admitted in an earlier post that it was overloaded by anything
more than a whip antenna!!


Not the point. It's easier to attenuate than to do almost anything else. Even
the radio itself can do that.

You would be far better off buying a dedicated HF receiver or a
transceiver with a far superior performance. They are available on Ebay
as well.


If you know of any that fit my description above, please name them.

Cable Shielding Misunderstandings
 

Lostgallifreyan wrote:
Jeff wrote in :

It is a perfectly adequate radio for what it was designed to be; a
portable that you take away on holiday to listen to BBC world service
on, but as for using it for anything more it is lacking.


Lacking what, specifically? I wanted a general purpose radio with full AM
coverage to 30 MHz, and I wanted it to be cheap and portable. Then I wanted
to give it a decent chance of getting signals when I'm not carrying it
around.

Chiming in late on this one.

The antenna isn't usually the limiting factor on modern radios. You'll
likely do as well with a random wire as a seriously engineered system.
Since you're only receiving, this is the case.

If you are wanting 500 KHz to 30 MHz, and you want full coverage, you'll
be hard pressed to beat a random length dipole and maybe give yourself a
little tuning cap on your end if you like. Just put up as much wire as
your space will permit, and there you go. This assumes that you use
ladder line to feed, not coax. For such a wide range antenna, ladder
line is the way to go.

That's going to wring out just about the last bit of performance you can
expect, unless you want to go to the bitter edge and construct
directional antennas. At the 500 KHz end, that will be a tad difficult.

Now for your application, the performance difference between a chunk of
wire, my random length dipole, and some directional gastraphagus will be
surprisingly little.

Use, or do not use the advice.

- 73 de Mike N3LI -

Cable Shielding Misunderstandings
 

Lostgallifreyan wrote:
Jeff wrote in :

It is a perfectly adequate radio for what it was designed to be; a
portable that you take away on holiday to listen to BBC world service
on, but as for using it for anything more it is lacking.


Lacking what, specifically? I wanted a general purpose radio with full AM
coverage to 30 MHz, and I wanted it to be cheap and portable. Then I wanted
to give it a decent chance of getting signals when I'm not carrying it
around.

As for a radio that that is only fit for getting BBC World Service, are you
sure you're not confusing the ATS-909 with whatever Sangean's original was,
as cloned by Roberts with model R9921? That really IS a basic radio designed
for that purpose, the ATS-909 does more.

Yes, but you were not talking about the other bands that it covers, you
only mentioned HF.


Even you admitted in an earlier post that it was overloaded by anything
more than a whip antenna!!


Not the point. It's easier to attenuate than to do almost anything else. Even
the radio itself can do that.

So why are you so worried about the co-ax and SNR, if you add an
attenuator in order to make the radio work properly you will also
attenuate any interference (and degrade your SNR).


You would be far better off buying a dedicated HF receiver or a
transceiver with a far superior performance. They are available on Ebay
as well.


If you know of any that fit my description above, please name them.

Virtually any comms receiver will give you coverage of AM to 30MHz, many
also have Band 2 vhf as well, they are too numerous to mention, but have
a look at this link and pick the ones that actuall have good RF performance:

http://www.eham.net/reviews/products/8

Jeff

Cable Shielding Misunderstandings
 

Jeff wrote in
:

Yes, but you were not talking about the other bands that it covers, you
only mentioned HF.


Fair enough, though I had mentioned it in earlier posts.


Even you admitted in an earlier post that it was overloaded by
anything more than a whip antenna!!


Not the point. It's easier to attenuate than to do almost anything
else. Even the radio itself can do that.

So why are you so worried about the co-ax and SNR, if you add an
attenuator in order to make the radio work properly you will also
attenuate any interference (and degrade your SNR).


Because I want to reduce the noise from stuff in the bulding compared to
whatever hits the whip antenna. Sure, attenuation might reduce SNR in a noisy
resistance (or subsequent gain stage) but NOT due to due to simple shrinkage
of scale (R = Ratio...), but that's why I want to get the SNR higher to start
with. It's the separation of internal noise signals from external wanted
signals that matters, same as for anyone using coax. Surely it's not suddenly
wrong because I'm doing it? If so, this isn't about science anymore.

If you know of any that fit my description above, please name them.

Virtually any comms receiver will give you coverage of AM to 30MHz, many
also have Band 2 vhf as well, they are too numerous to mention, but have
a look at this link and pick the ones that actuall have good RF
performance:

http://www.eham.net/reviews/products/8


Thanks, that will be useful. The ATS-909 is just a starting point. I want to
have tried it, even if I just sell it on. (Was why I bought it used, that way
I won't lose out).

Cable Shielding Misunderstandings
 

Lostgallifreyan wrote:

No. It's called 'go see for yourself and tell me based on YOUR judgement if
it's worth revisiting'. If all I wanted was a pat on the head I wouldn't even
have provided a link. Either that info has technical merit, or it doesn't in
which case perhaps you should berate THEM and not me!

Of course it has no technical merit, it is just words! Some of them are
pretty ambiguous too, like that "video Frequencies" bit. Are the video
frequencies they refer to The frequencies that television signals are
broadcast or are tehy the frequencies that a video signal uses. THere is
a difference.

There's more. From that paragraph above, your not asking us to do your
research for you, are you?

- 73 de Mike N3LI -

Cable Shielding Misunderstandings
 

Richard Clark wrote:

We have your dozen or more suppositions filtered through anonymous and
linked-to sources of indifferent quality that each in their own right
have issues with a spectrum of cable types


I read that as "suppositories" instead of suppositions, Richard. Perhaps
both may be right? 8^)

Cable Shielding Misunderstandings
 

Michael Coslo wrote in
:

Lostgallifreyan wrote:

No. It's called 'go see for yourself and tell me based on YOUR
judgement if it's worth revisiting'. If all I wanted was a pat on the
head I wouldn't even have provided a link. Either that info has
technical merit, or it doesn't in which case perhaps you should berate
THEM and not me!

Of course it has no technical merit, it is just words! Some of them are
pretty ambiguous too, like that "video Frequencies" bit. Are the video
frequencies they refer to The frequencies that television signals are
broadcast or are tehy the frequencies that a video signal uses. THere is
a difference.

There's more. From that paragraph above, your not asking us to do your
research for you, are you?

- 73 de Mike N3LI -


It's not that bad. I've seen far worse. And no, I'm not asking you or anyone
else to do anything. When I'm not checking here and replying I'm reading
other stuff. I'll doing more of that because it doesn't argue so much.

Cable Shielding Misunderstandings
 

Michael Coslo wrote in
:

Richard Clark wrote:

We have your dozen or more suppositions filtered through anonymous and
linked-to sources of indifferent quality that each in their own right
have issues with a spectrum of cable types


I read that as "suppositories" instead of suppositions, Richard. Perhaps
both may be right? 8^)


Careful. Don't worry about mine, worry about the one you might seem to be
licking. :)

Cable Shielding Misunderstandings
 

On Wed, 03 Feb 2010 14:06:05 -0500, Michael Coslo
wrote:

Richard Clark wrote:

We have your dozen or more suppositions filtered through anonymous and
linked-to sources of indifferent quality that each in their own right
have issues with a spectrum of cable types


I read that as "suppositories" instead of suppositions, Richard. Perhaps
both may be right? 8^)

Reminds me of the old joke about the Engineer's problem with
constipation: he worked it out with a slide rule.

Mathematician, pencil
Draftsman, compass
antenna designer, gin pole
..... and so on.
you get the point.

73's
Richard Clark, KB7QHC

Cable Shielding Misunderstandings
 

Lostgallifreyan wrote:
Jeff wrote in :

Any receiving equipment you get will almost certainly have a 50 ohm
(nominal!) input, so any higher antenna impedances will need to be
matched back to 50ohms anyway. How much loss you will encounter by using
75ohm cable will depend on the actual set up.


Apparently no-one knows the impedance of a Sangean ATS-909 radio, I've asked
several people, at least one of whom specialises in modifying that radio.

Perhaps there is a reason. It isn't terribly important at all.

Looks like 1K is best guess based on schematic. Loss won't bother me so much
as SNR. Several people advised that a 15 foot vertical whip is likely to
overload the input so loss is not my main concern.

Not to be overly precise, but the whip won't overload your radio, strong
signals might. Those little radios are pretty sensitive.

So what are you trying to do here, aside from get an external signal
into a radio? If you want to have an audiophile grade antenna system,
you need to go out and get some good hardline coax*. You can also make
some measurements to determine the exact input impedance of your radio,
then construct a balun to match it to the rest of the system. If
measurement isn't your thing, you can probably get by with a 9:1 balun,
as a back of the envelope calculation.

Then if you can put them in, you need around 120 radials that you use
for the ground on your antenna. You can either elevate them, lay them on
the ground, or shallow bury them. If you have a wife the third option is
probably what you want to do.

There are other little tweaks, such as silver contacts, a good quality
tuner, and probably some I haven't thought about yet. Some still hold
out for low oxygen copper.

Do all that, and you can still do pretty close to the results with a
long wire hanging out of your window.

Now if you get a communications grade radio, some of my less tongue in
cheek suggestions might help more. But make no mistake, you are deep
into the world of diminishing returns.

note 1.

Coolest hardline I ever saw was at a TV station. It was about a foot in
diameter on the jacket, and I didn't see the center conductor, but my
best guess is that it was around 2 inches in diameter.

note 2.

I'm not trying to be rude, but you've been getting some good info in
here, you're just not taking it. Reminds me of some of the students
coming out of college these days with a nice fresh bachelor's degree.
They don't accept input, and think they should be promoted for showing
up on time.

- 73 de Mike N3LI -