Lostgallifreyan wrote:
Richard Clark wrote in
:

I like their discussion on materials (which fits my own
view on that subject), and on types of RG6. I just started in on the one
about 'quad screens'.
This is called confirmatorial bias which means you justify a thought
on the basis of having found a source that repeats it back to you.


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! You expect me to fully
understand details beyond need, yet you won't even take a look at something
signposted right in front of you is an adequate source of info to learn from.
If you can't do that much, why should I trust your judgement? I'll make up my
own mind anyway. Between my efforts, and the other posts here, I have got my
answers.

Face up to the disillusion being presented in this painted into the
corner scenario you are in. The cheapest cable will probably work as
best as any sensible solution has to offer, simply because your
perceived situation hasn't any prospect of being solved by that choice
of line, or any other.


Well, that's just nonsense. Grandstanding nonsense at that. You just baldly
stated that no cable can fix whatever my problem might be, purely because YOU
can't see what it is. You're painting me into a corner. I'm trying to get out
of one. There's no technical point in what you just said. At least I try.
With your knowledge, you should know better.

Other people here, (and in the pages I linked to but you didn't apparently
see) have shown that foil can be so bad, either from tearing, or dubious
contact, that it's unwise to use it except in fixed situations where you know
it will be ok, and not for someone who is likely to want to reuse a cable
while trying new ideas, or to grab more off the reel to try something else.
I've seen that RG6 types vary so much that there's no point citing its name.
Considering I never used to, and already knew that 75 ohms is a result of
precisely controlled sizes and manufacturing tolerances, I was probably
better off before I saw people telling me that distinctions between RG6 and
RG59 were important. Their context isn't the same as mine. My needs are more
likely to be satisfied by a BT data coax than a satellite coax.

As a matter of interest why are you looking at 75ohm cable, when most
people and equipment use 50ohm.

Jeff

Jeff wrote in :

As a matter of interest why are you looking at 75ohm cable, when most
people and equipment use 50ohm.


Good point, though last I read of that, it was the other way round.
(Depends on context). At least, most times I had a device that needed RF
coax, it specified 75 ohms if it didn't come with cables made for it. In my
current case, it's not clearly known what other impedances are involved in
an SWL setup, but they're almost certainly higher than 75 ohms, so going for
a 50 ohm coax seems unwise.

Lostgallifreyan wrote:
Jeff wrote in :

As a matter of interest why are you looking at 75ohm cable, when most
people and equipment use 50ohm.


Good point, though last I read of that, it was the other way round.
(Depends on context). At least, most times I had a device that needed RF
coax, it specified 75 ohms if it didn't come with cables made for it. In my
current case, it's not clearly known what other impedances are involved in
an SWL setup, but they're almost certainly higher than 75 ohms, so going for
a 50 ohm coax seems unwise.

Virtually all radio equipment is standardized on 50 ohms, with the
exception of CATV etc.

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.

Jeff

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.
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.

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.
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.

1K is just a guess as it is just one component in the antenna input
circuit.

Also, nobody observed that the input impedance of the radio can vary
significantly with the setting of the "RF Gain" control.

Crude measurements on a DX-398 show the impedance near 85 ohms at 'max'
gain and near 280 ohms at 'min' gain. The measurements were crude and
the error could be 20%. Use these numbers with caution.

There are no guarantees that the input impedance does not change with
frequency, either.

joe wrote:

1K is just a guess as it is just one component in the antenna input
circuit.

Also, nobody observed that the input impedance of the radio can vary
significantly with the setting of the "RF Gain" control.

Crude measurements on a DX-398 show the impedance near 85 ohms at 'max'
gain and near 280 ohms at 'min' gain. The measurements were crude and
the error could be 20%. Use these numbers with caution.

There are no guarantees that the input impedance does not change with
frequency, either.

The Sangean ATS-909 appears to operate no higher than 30 MHz. In the HF
range, antenna efficiency and transmission line mismatch have no
significant effect on the signal/noise ratio (unless the system is
exceptionally lossy and/or the receiver exceptionally noisy, neither
very likely), hence they don't affect your ability to hear stations.

Roy Lewallen, W7EL

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.
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.

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!!

Jeff

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.

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!!!

Jeff

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 -