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).

It is really more the difference in consideration between the coax and
the radio that strikes me. You are making a huge fuss over the coax, but
appear to have little consideration over the radio which is a far more
important issue. You seem to be set on the Sagen when it is is far from
the best solution, but nit picking over the coax, which in reality most
likely won't make a shred of difference.

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.

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

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.

Jeff

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.

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 -

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

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).

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.



Well firstly, adding an attenuator WILL degrade the Noise Figure of your
receiver.

Now whether this will have any significance depends on the original NF
of the receiver, and the level of External noise (atmospheric and man made).

It we take your 'ideal' set-up where you have eliminated the pick-up in
the building; you SNR will depend on the NF of the rx and the levels of
signal and received noise at the antenna.

So if we have to put an attenuator in line to make the rx happy so it
does not overload, then we will have degraded the rx's NF by the value
of the attenuator. So say a 10db attenuator will have degraded you NF by
10dB. It will also have degraded the level of input signal by 10dB, so
you have a double wammy.

Now the effect on your SNR will depend on which band you are listening
on ant the level of atmospheric noise compared to the NF of the rx. At
lower frequencies the effect will be less because the atmospheric noise
is greater and will swamp the rx NF to some degree. As you go up in
ferquency the NF will start to become dominant.


If we take the case of leaky coax and pick-up in the building, sure the
picked up noise will degrade the SNR, but the leakage is likely to be
very small in absolute level and adding any attenuation will take it
below the noise floor anyway. The differences in leakage between the
types of coax under discussion will be insignificant compared to the
attenuation values you will have to add to make the rx happy. That is
why I questioned the choice or rx, having to add attenuation negates the
need to have the ultimate in screening unless the pick-up is a very
high level (in which case you are stumped anyway).

Also if your building is that noisy then there will be significant noise
pick-up directly into the antenna which you can do nothing about. There
is a significant possibility that this will be much greater than any
direct leakage into the cable making such pick-up insignificant.

Perhaps you should tell us why you think there will be this pick-up and
what you think the source is in the building. That will help you get a
sensible answer.

One final point, you say "It's the separation of internal noise signals
from external wanted signals that matters, same as for anyone using
coax." I suspect that is about the last thing that most people think
about when choosing coax, they normally think about the impedance first,
then the transmission loss, size and cost. I doubt if the "the
separation of internal noise signals from external wanted signals"
crosses their minds at all!!

Jeff

On Thu, 04 Feb 2010 09:20:10 +0000, Jeff
wrote:

One final point, you say "It's the separation of internal noise signals
from external wanted signals that matters, same as for anyone using
coax." I suspect that is about the last thing that most people think
about when choosing coax, they normally think about the impedance first,
then the transmission loss, size and cost. I doubt if the "the
separation of internal noise signals from external wanted signals"
crosses their minds at all!!

Hi Jeff,

You will undoubtedly have two camps there. As for those expecting
"the separation of internal noise signals from external wanted signals"
then they will be dissappointed or live happily with illusion; and the
others will, as you say, will select their transmission line (not
solely a coax) on the basis of those qualities they can expect it to
deliver.

The reason why I opened this up to include parallel line is that too
much superstitious quality has been attached to a shield. This has
been tangentially supported by measure of the cable transfer impedance
with the hope of using that to predict shielding efficiency. The
ordinary reader is left with the impression that by focusing on a
shield that the state of shielding is defined at the alter of the
coax. It is not.

"Cable transfer impedance" is measured in a highly defined manner with
an example of a very good graphic found at:
http://www.emcconsultinginc.com/docs/beldenTiAndSe.pdf

Replace the well grounded coax with a parallel line with its balanced
load and balanced source, and the transfer impedance for that system
will reveal shielding efficiencies easily equal to, or better than,
coaxial cables. That efficiency will vary by the degree to the
proximity of the parallel line to the ground plane, and its geometry.
This geometry is manageable with parallel lines, the coax has to live
with what it has.

Now, this counter argument is based upon the premise of the near
sighted quest for some goal that is achieved by the coaxial line alone
- in other words, a folly. However, what this counter argument does
is penetrate the balloon of complacency surrounding the investment of
superstitious qualities in successive layers of shielding. Without
care, those extra layers can inject MORE noise into the system than
that which exists in the environment. I have already written and
supplied reference to that unfortunate side effect to no obvious
comment about this paradox.

73's
Richard Clark, KB7QHC