Creating Large Ferrite Antenna tuned to 457khz range?
 

I'm trying to create a largish ferrite receiver antenna tuned
exclusively to the 457khz range. I was going to get the ferrite rod
from he

http://www.stormwise.com/page26.htm

As I only need the single frequency I was wondering if it was more
effective to make a self-resonant antenna?, or does a capacitor not
decrease quality of the single?

Secondlly, I have very little experience in the radio world, and was
considering following am radio plans similar to this to attach my
antenna to:
http://www.stormwise.com/page56.htm

Just swapping the variable capacitor for a fixed one tuned to my
frequency.

Is this the optimal way to get the strongest signal? Can anyone point
me in a direction to get more information on how to build such a
receiver? Most important is the range of the antenna in picking up
very weak signals.

Thanks,
Chris

Creating Large Ferrite Antenna tuned to 457khz range?
 

On Dec 11, 9:18 am, cmor wrote:
I'm trying to create a largish ferrite receiver antenna tuned
exclusively to the 457khz range. I was going to get the ferrite rod
from he

http://www.stormwise.com/page26.htm

As I only need the single frequency I was wondering if it was more
effective to make a self-resonant antenna?, or does a capacitor not
decrease quality of the single?

Secondlly, I have very little experience in the radio world, and was
considering following am radio plans similar to this to attach my
antenna to:http://www.stormwise.com/page56.htm

Just swapping the variable capacitor for a fixed one tuned to my
frequency.

Is this the optimal way to get the strongest signal? Can anyone point
me in a direction to get more information on how to build such a
receiver? Most important is the range of the antenna in picking up
very weak signals.

Thanks,
Chris

Are you trying to build a better avalanche receiver or what? The
trancievers available today seem to be pretty good.

Paul, KD7HB

Creating Large Ferrite Antenna tuned to 457khz range?
 

On Dec 11, 9:18 am, cmor wrote:
I'm trying to create a largish ferrite receiver antenna tuned
exclusively to the 457khz range. I was going to get the ferrite rod
from he

http://www.stormwise.com/page26.htm

As I only need the single frequency I was wondering if it was more
effective to make a self-resonant antenna?, or does a capacitor not
decrease quality of the single?

Secondlly, I have very little experience in the radio world, and was
considering following am radio plans similar to this to attach my
antenna to:http://www.stormwise.com/page56.htm

Just swapping the variable capacitor for a fixed one tuned to my
frequency.

Is this the optimal way to get the strongest signal? Can anyone point
me in a direction to get more information on how to build such a
receiver? Most important is the range of the antenna in picking up
very weak signals.

Thanks,
Chris

What specific kind of signals are you trying to pick up, and what is
it that will prevent you from hearing them? That is, if the signals
are buried in atmospheric noise, a more "sensitive" antenna that also
picks up more noise as well as more signal isn't going to help the
signal-to-noise ratio. For that, you may need to use some additional
knowledge about the signal that you can use to differentiate it from
the noise. At 457kHz, atmospheric noise is very high amplitude, and
it doesn't take much of an antenna plus receiver to get all the signal
that will do you any good.

On the other hand, if the thing that keeps you from hearing the
desired signal is an interfering signal, the null of a loop (or
ferrite rod) antenna can be used to get rid of that signal that comes
from one direction (which lets you listen more easily to the desired
signal, provided your desired signal isn't coming from the same
direction).

Cheers,
Tom

Creating Large Ferrite Antenna tuned to 457khz range?
 

AI4QJ wrote:

As another poster said, there is very high noise at this frequency. The way
this radio works is to use the coil as both an antenna and the resonating
inductance in the tuned circuit. I have found that, in high noise
applications like this, often the best way to get a clear signal is to
off-tune the receiving antenna, for example, tuning the receiving circuit to
the frequency you need but using a shorter antenna. A 40m antenna often
works well for receiving 80m and 160m stations without all the noise. . .

Do you mean you can get a better signal/noise ratio with a 40 m antenna
on 80 or 160 than with a half wave 80 or 160 meter antenna? If so, what
do you suppose the mechanism is by which the shorter antenna
distinguishes between signal and noise?

I've seen cases where a receiver designed for use with a small whip
antenna became overloaded when connected to a decent antenna. Adding
attenuation or using a shorter antenna improved the S/N ratio because a
lot of the noise was due to intermod from the receiver overloading. I've
never seen this with a decent receiver, however.

Roy Lewallen, W7EL

Creating Large Ferrite Antenna tuned to 457khz range?
 

"AI4QJ" wrote in
:


"Roy Lewallen" wrote in message
...
AI4QJ wrote:

As another poster said, there is very high noise at this frequency.
The way this radio works is to use the coil as both an antenna and
the resonating inductance in the tuned circuit. I have found that,
in high noise applications like this, often the best way to get a
clear signal is to off-tune the receiving antenna, for example,
tuning the receiving circuit to the frequency you need but using a
shorter antenna. A 40m antenna often works well for receiving 80m
and 160m stations without all the noise. . .

Do you mean you can get a better signal/noise ratio with a 40 m
antenna on 80 or 160 than with a half wave 80 or 160 meter antenna?

....
When other people complianed of noise, it was a common practice for
them to use 2 transceivers or a transmitter with a separate receiver
on 75 80m. The transmitter of course was tuned as close to 1:1 as
possible but the receiver was tuned to a higher VSWR to 'tune-out' the
noise, yet the signals higher than noise came through very well....

I note you are distancing yourself somewhat from this explanation, but
apparently supporting it. A foot in both camps.

Is the assertion supported by any sound technical explanation.

Roy gave one possible explanation of why reducing receiver input may
improve S/N ratio, but you later dismiss that (RX IMD noise) as a likely
explanation.

Fundamentally, wouldn't you expect S/N to degrade in a linear receiver
system as you decrease the Signal+Off-Air-Noise wrt the receiver
equivalent internal noise?

Have you actually measured and documented the claimed improvement, or can
you cite a reliable experiment? Can you really dismiss RX IMD noise as a
significant contribution? Do you have another likely explanation?

This was/is something other people do routinely and is somewhat better
than an old wivws tale. Of course, by not tuning in the noise, you

So, if it cannot be measured, if it cannot be explained, isn't it no more
than an old wives tale?

Owen

Creating Large Ferrite Antenna tuned to 457khz range?
 

AI4QJ wrote:
. . .
When other people complianed of noise, it was a common practice for them to
use 2 transceivers or a transmitter with a separate receiver on 75 80m. The
transmitter of course was tuned as close to 1:1 as possible but the receiver
was tuned to a higher VSWR to 'tune-out' the noise, yet the signals higher
than noise came through very well. I was actually quite surprized to find
out how much noise there was on 75-80m when I was actually able to
transmit/receiver at a VSWR close to 1:1.

This was/is something other people do routinely and is somewhat better than
an old wivws tale. Of course, by not tuning in the noise, you risk not
tuning in the very weak stations but you can come to an accomodation where
you hear mostly what you want to hear while getting rid of noise. The
attenuate button does not work as well for this (my opinion).

If so, what do you suppose the mechanism is by which the shorter antenna
distinguishes between signal and noise?

If the antenna has a high VSWR, although you cannot transmit efficiently,
signals significantly stronger than noise level can still be received, or so
I think as do others. I am not sure at this time 'why' the gain of the noise
is not comparable to that of stronger signals when adjusting the receicver
for normal listening volumes. But when listing at 80m, you can simply take a
20 foot piece of wire and hang it indoors and you will hear a lot of
stations quite clearly and the noise level will be much lower than when you
tune it resonant.
. . .

Certainly the noise level will be lower than when you match the antenna.
but so will the signals. In exactly the same ratio. And if you can hear
the signals clearly with the short antenna, you can hear them just as
clearly with the longer one -- unless you're overdriving something to
the point of nonlinearity with the longer antenna.

If you think you're actually improving the signal/noise ratio by
mismatching the antenna, then you've claiming that mismatching has
somehow given it the ability to tell the difference between what you
regard as "signal" and what you regard as "noise" even though both are
presumably on the same frequency. Or perhaps if the signal and noise are
coming from a different direction, the mismatch is causing a change in
the antenna's directional pattern. Neither of these fits with any known
theory, so I'd have to see some really solid quantitative measurements
to be convinced this is more than an old wives' tale. (And even then,
I'd be looking very hard for an explanation that fits the theory which
has suited us so well for over a century.)

Mismatching the antenna should do no more nor less than turning down the
RF gain control. Have you tried doing that instead?

Roy Lewallen, W7EL

Creating Large Ferrite Antenna tuned to 457khz range?
 

cmor wrote:

...
Thanks,
Chris

Don't worry about the noise.

Construct the best possible setup you can. Pay close attention to
matching the impedance to the receiver. Use quality/high-freq
semiconductors, even better than required/stated--if possible, keep
those noise figures low. Remove the antenna away from any potential
noise source as you possibly can. Keep the antenna as high as you
possibly can. Place the antenna where it will get the largest possible
view of the heavens/horizon. Use as Hi-Q coil/cap as you can, to narrow
the bandwidth as much as can be logically tolerated. Keep the
coax/feeder as short as is logically possible and the run away from
noise sources. Etc. ...

Now, worry about what you can do to help with noise reduction ... if you
find you have too much gain, drop a gain control in ... filters?

Regards,
JS

Creating Large Ferrite Antenna tuned to 457khz range?
 

Owen Duffy wrote:
. . .
Fundamentally, wouldn't you expect S/N to degrade in a linear receiver
system as you decrease the Signal+Off-Air-Noise wrt the receiver
equivalent internal noise?
. . .

I wouldn't expect it to change by any discernible amount at HF, until
the antenna gets very short or very mismatched. The noise figure of most
HF receivers is good enough, and the atmospheric noise high enough, that
it takes a poor antenna indeed before the receiver noise becomes
apparent. This is certainly emphatically true on 80 and 160 meters in
Florida.

Roy Lewallen, W7EL

Creating Large Ferrite Antenna tuned to 457khz range?
 

Roy Lewallen wrote in
:

Owen Duffy wrote:
. . .
Fundamentally, wouldn't you expect S/N to degrade in a linear
receiver system as you decrease the Signal+Off-Air-Noise wrt the
receiver equivalent internal noise?
. . .

I wouldn't expect it to change by any discernible amount at HF, until
the antenna gets very short or very mismatched. The noise figure of
most HF receivers is good enough, and the atmospheric noise high
enough, that it takes a poor antenna indeed before the receiver noise
becomes apparent. This is certainly emphatically true on 80 and 160
meters in Florida.

Agreed Roy.

My graphic at http://www.vk1od.net/bpl/AreYouReady.htm shows the IRU-R
P.372-8 predicted galactic noise levels to be some 35dB above a good
receiver noise floor at 80m, and man made noise and especially
atmospherics are well above that.

Harking back to IMD noise, it is a result of non-linearity in the
receiver (front end usually), and can be improved by reducing the level
of unwanted (ie out of band) signals reaching the electronics. Any form
of front end filtering (like a detuned ATU) that favours out of band
signals relative to inband will only exacerbate IMD noise, not improve
it, so the proposed technique should not improve IMD noise.

As you noted, IMD noise can be an issue with a substandard receiver...
for example I experience it with an Icom IC-R20 on a half wave dipole on
80m. I agree with you that most good receivers should have very low
noise from IMD, so that AI4QJ's proposition without an apparent
explanation.

Owen

Creating Large Ferrite Antenna tuned to 457khz range?
 

"AI4QJ" wrote in
:

....
Roy gave one possible explanation of why reducing receiver input may
improve S/N ratio, but you later dismiss that (RX IMD noise) as a
likely explanation.

No I did not!

First I said "There were no front end overload effects; the
signals were located skip distances for 75-80m with nothing local
nearby

But then I said:

"(except maybe "noise", and it just occurs to me that local "noise"
from powerlines or whatever could be overloading my front
end...hmmm...not sure)."

Which is another way of saying "Hey, maybe you're right. Maybe strong
signals from locally generated noise IS overloading my front end."

The full paragraph was:
For me, Yeasu 747 and icom IC718 (as you can see on my QRZ photo). These
are fairly decent receivers. There were no front end overload effects;
the signals were located skip distances for 75-80m with nothing local
nearby (except maybe "noise", and it just occurs to me that local
"noise" from powerlines or whatever could be overloading my front
end...hmmm...not sure)"

I have interpreted "For me, Yeasu 747 and icom IC718 (as you can see on
my QRZ photo). These are fairly decent receivers. There were no front end
overload effects;" to be fairly definite.

"There were no front end overload effects;", it is about as clear as "I
did not have sex with that women"... but we all know what theat mean't.

I am not trying to misrepresent you, it is about the value you put in
your own written words.

Owen