"William Mutch" wrote in message
l.edu...
I used to think that passive antenna tuners or matching networks
were worthless, but over the weekend I got some real SWL evidence to the
contrary.
My prime RCVR is a Sat800 refurb hooked to 156 feet of AWG 16 hard
drawn stranded, oriented NNW/SSE up about 40 feet between two large
trees and fed off center at the 1/3 // 2/3 point with twin RG6U which
comes down to a 4:1 balun outdoors at a decent ground (copper ground
pipe filled with copper sulfate, steel well casing and cast iron soil
pipe bonded together with coax braid.) Coax from the balun goes into the
house to the RCVR.
One thing about the Sat800 has always bothered me...there's no way
to turn the AGC *off*, so the noise floor is always rushing up to blast
you in the headphones when you tune between stations. I'd previously
not been able to receive anything but a couple of local aero beacons on
longwave, nor anything but the Christian megawatt at 3200 on the 90
meter band. I didn't care much about the longwave since the very useful
aviation weather Elmira NY on 385 khz was replaced by better service on
162.40 Mhz vhf.
Last week, just for fun I made a Hi-Q parallel resonant tank for
longwave from a 385 pf variable cap and a 3.850 mh inductor.
(82 turns
#24 awg wire on a 1.3" audio toroid core) This tunes 520 khz down to 170
khz with a pronounced peak.

A disclaimer: I may be totally wrong about this, but I think what you built
is actually more like a sharp-tuned preselector than an antenna tuner,
because it's not resonating your antenna system or improving the impedance
mismatch, so much as it's favoring signals around the frequency of interest
over signals that are outside this range.

This would reduce the stress on your receiver's front end by attenuating
out-of-band signals. You can verify this (or disprove it) by comparing a
signal at say, 15 Mhz with and without your matching network installed. If
your HF signals drop in strength, this may explain why reception is so much
better with the parallel resonant circuit in place.

It's my understanding that a substantial antenna like yours will pick up
many volts of total RF at a very wide range of frequencies. These
components stress your front end, driving it into non-linearity and causing
mixing products, some of which will fall within the passband of the LF
signal you're trying to hear. This is experienced as a higher noise level.
The pre-selector knocks down these out-of-band signals, dramatically
reducing the amount of rmixing and thus reducing the background noise level.

I'm EXTREMELY skeptical of any claim that impedance matching by itself will
make any difference to HF reception once you have more than (say
arbitrarily) twenty feet of wire antenna, unless you're feeding a crystal
set. The reason why is, external noise is so high at HF that increasing
the efficiency of energy transfer increases the efficiency of noise transfer
just exactly as much as it increases the efficiency of signal transfer,
resulting in a net 0 dB change in signal-to-noise ratio. You get higher
S-meter readings, but no change in signal readability.

Preselection, on the other hand, should never hurt and would help in cases
where the receiver is overstressed by total signal levels.

This is one possible explanation for your results. Again, I'm not certain
this is correct. However, if you notice a big drop in signal level well up
the HF spectrum when your network is installed, this would be plausible at
least.

-- Ross

I coupled it very loosely (2 1/2 turns) to
the coax near the RCVR and was astounded at the difference in reception.
Around 0500Z I logged 15 different aero beacons at between 260 and 420
khz ! The tuned circuit didn't bring the signal levels up...it took
the noise floor DOWN ! Same thing happened when I picked up a used
Barker & Williamson AT-300 Tee section tuner at a hamfest last weekend.
The peaks are not as pronounced as the longwave tank, but the 90 meter
band yielded a half dozen African stations where previously I'd heard
nothing but QRMN.
On some frequencies the most dramatic improvement came where the
peak in signal strength and the peak in noise came at slightly different
settings of the tuner. This to me is evidence that nearby noise sources,
even when filtered out of the detector and audio in the receiver are
still affecting the AGC line, turning down the effective signal. Seems
like an active preselector will help if you can't get an antenna out in
the clear, but even if you can, some more selectivity *before* the front
end of the receiver can help. I'm a convert.

Ross Archer wrote:

A disclaimer: I may be totally wrong about this, but I think what you built
is actually more like a sharp-tuned preselector than an antenna tuner,
because it's not resonating your antenna system or improving the impedance
mismatch, so much as it's favoring signals around the frequency of interest
over signals that are outside this range.

This would reduce the stress on your receiver's front end by attenuating
out-of-band signals. You can verify this (or disprove it) by comparing a
signal at say, 15 Mhz with and without your matching network installed. If
your HF signals drop in strength, this may explain why reception is so much
better with the parallel resonant circuit in place.

It's my understanding that a substantial antenna like yours will pick up
many volts of total RF at a very wide range of frequencies. These
components stress your front end, driving it into non-linearity and causing
mixing products, some of which will fall within the passband of the LF
signal you're trying to hear. This is experienced as a higher noise level.
The pre-selector knocks down these out-of-band signals, dramatically
reducing the amount of rmixing and thus reducing the background noise level.

I'm EXTREMELY skeptical of any claim that impedance matching by itself will
make any difference to HF reception once you have more than (say
arbitrarily) twenty feet of wire antenna, unless you're feeding a crystal
set. The reason why is, external noise is so high at HF that increasing
the efficiency of energy transfer increases the efficiency of noise transfer
just exactly as much as it increases the efficiency of signal transfer,
resulting in a net 0 dB change in signal-to-noise ratio. You get higher
S-meter readings, but no change in signal readability.

Preselection, on the other hand, should never hurt and would help in cases
where the receiver is overstressed by total signal levels.

This is one possible explanation for your results. Again, I'm not certain
this is correct. However, if you notice a big drop in signal level well up
the HF spectrum when your network is installed, this would be plausible at
least.

-- Ross

I coupled it very loosely (2 1/2 turns) to
the coax near the RCVR and was astounded at the difference in reception.
Around 0500Z I logged 15 different aero beacons at between 260 and 420
khz ! The tuned circuit didn't bring the signal levels up...it took
the noise floor DOWN ! Same thing happened when I picked up a used
Barker & Williamson AT-300 Tee section tuner at a hamfest last weekend.
The peaks are not as pronounced as the longwave tank, but the 90 meter
band yielded a half dozen African stations where previously I'd heard
nothing but QRMN.
On some frequencies the most dramatic improvement came where the
peak in signal strength and the peak in noise came at slightly different
settings of the tuner. This to me is evidence that nearby noise sources,
even when filtered out of the detector and audio in the receiver are
still affecting the AGC line, turning down the effective signal. Seems
like an active preselector will help if you can't get an antenna out in
the clear, but even if you can, some more selectivity *before* the front
end of the receiver can help. I'm a convert.

I thought your choice of the word "stress" (above) was curious. I've
never seen that word used in the context of overloading a receiver's
front-end. I'm sure you know that signal overloading doesn't actually
damage anything in the radio, so what does "stress" mean to you in this
case? Just curious.


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= = = William Mutch wrote in message
= = = ll.edu...

I used to think that passive antenna tuners or matching
networks were worthless, but over the weekend I got some
real SWL evidence to the contrary.
My prime RCVR is a Sat800 refurb

hooked to 156 feet of AWG 16 hard drawn stranded, oriented NNW/SSE
up about 40 feet between two large trees and

* This Antenna sounds Long and High Enough.

fed off center at the 1/3 // 2/3 point

* Sounds 'sort-of-like' a WINDOM (52 Ft & 104Ft) Antenna
that is configured with Two un-equal Top Arms 'elements':
+ 156 Feet = 1WL @ 6.4 MHz & 1/2WL @ 3.2 MHz & 1/4WL @ 1.6 MHz
+ 104 Feet = 1WL @ 9.7 MHz & 1/2WL @ 4.8 MHz & 1/4WL @ 2.4 MHz
+ 52 Feet = 1WL @ 19.3 MHz & 1/2WL @ 9.7 MHz & 1/4WL @ 4.8 MHz
http://www.packetradio.com/windom.htm

with twin RG6U which comes down to a 4:1 balun

* Then sounds like a G5RV Down Leg 'elements'.
http://www.qsl.net/aa3px/g5rv.htm

outdoors at a decent ground (copper ground pipe filled
with copper sulfate, steel well casing and cast iron soil
pipe bonded together with coax braid.)

* The Ground sounds solid enough.

* READ: Compilation of "Ground" Messages
http://groups.yahoo.com/group/Shortw...na/message/524

Coax from the balun goes into the house to the RCVR.

* A Coax Feed-in-Line is always a Good Idea )

One thing about the Sat800 has always bothered me...there's no way
to turn the AGC *off*, so the noise floor is always rushing up to blast
you in the headphones when you tune between stations. I'd previously
not been able to receive anything but a couple of local aero beacons on
longwave, nor anything but the Christian megawatt at 3200 on the 90
meter band. I didn't care much about the longwave since the very useful
aviation weather Elmira NY on 385 khz was replaced by better service on
162.40 Mhz vhf.

Last week, just for fun I made a Hi-Q parallel resonant tank
for longwave from a 385 pf variable cap and a 3.850 mh inductor.
(82 turns #24 awg wire on a 1.3" audio toroid core)

* Sounds like a fairly good Tuned Circuit for your targeted
Longwave Frequency Range.

* FWIW: Sounds like what you have may be more of a Longwave
Signal "Pre-Selector" then an 'general' Antenna Tuner.

* Read - Why:: Baluns -v- Antenna Tuner -v- Pre-Selector
-v- Modern Radio/Receivers
http://groups.yahoo.com/group/Shortw...na/message/728

This tunes 520 khz down to 170 khz with a pronounced peak.
I coupled it very loosely (2 1/2 turns) to the coax near the
RCVR and was astounded at the difference in reception.
Around 0500Z I logged 15 different aero beacons at between
260 and 420 khz !

* Again sounds like your basic tuned circuit works for the intended
Longwave Band Area.

The tuned circuit didn't bring the signal levels up...it took
the noise floor DOWN !

* You may have obtained/gain the same Noise Reduction results
by simply using a Lead-in-Line Isolator 1:1 Matching Transformer
between the Coax Cable Feed-in-Line and the Receiver.

* READ - Wellbrook "Low Noise Antenna" 'design concept' using
two components that WellBrook manufactures: the Universal Magnetic
Balun (UMB) and the Antenna Feed Isolator.
ISOLATOR= http://www.wellbrook.uk.com/longwire.html
http://groups.yahoo.com/group/Shortw...na/message/675
NOTE: Please Read Wellbrooks Claims at the bottom of the webpage
concerning how the "Isolator" can 'reduce' Noise at Low Frequencies
by up to 40 dB.

Same thing happened when I picked up a used Barker & Williamson
AT-300 Tee section tuner at a hamfest last weekend.
The peaks are not as pronounced as the longwave tank, but the 90 meter
band yielded a half dozen African stations where previously I'd heard
nothing but QRMN.

On some frequencies the most dramatic improvement came where the
peak in signal strength and the peak in noise came at slightly different
settings of the tuner. This to me is evidence that nearby noise sources,
even when filtered out of the detector and audio in the receiver are
still affecting the AGC line, turning down the effective signal. Seems
like an active preselector will help if you can't get an antenna out in
the clear, but even if you can, some more selectivity *before* the front
end of the receiver can help.
I'm a convert.

iane ~ RHF

..

"starman" wrote in message ...
Ross Archer wrote:

A disclaimer: I may be totally wrong about this, but I think what you built
is actually more like a sharp-tuned preselector than an antenna tuner,
because it's not resonating your antenna system or improving the impedance
mismatch, so much as it's favoring signals around the frequency of interest
over signals that are outside this range.

This would reduce the stress on your receiver's front end by attenuating
out-of-band signals. You can verify this (or disprove it) by comparing a
signal at say, 15 Mhz with and without your matching network installed. If
your HF signals drop in strength, this may explain why reception is so much
better with the parallel resonant circuit in place.

It's my understanding that a substantial antenna like yours will pick up
many volts of total RF at a very wide range of frequencies. These
components stress your front end, driving it into non-linearity and causing
mixing products, some of which will fall within the passband of the LF
signal you're trying to hear. This is experienced as a higher noise level.
The pre-selector knocks down these out-of-band signals, dramatically
reducing the amount of rmixing and thus reducing the background noise level.

I'm EXTREMELY skeptical of any claim that impedance matching by itself will
make any difference to HF reception once you have more than (say
arbitrarily) twenty feet of wire antenna, unless you're feeding a crystal
set. The reason why is, external noise is so high at HF that increasing
the efficiency of energy transfer increases the efficiency of noise transfer
just exactly as much as it increases the efficiency of signal transfer,
resulting in a net 0 dB change in signal-to-noise ratio. You get higher
S-meter readings, but no change in signal readability.

Preselection, on the other hand, should never hurt and would help in cases
where the receiver is overstressed by total signal levels.

This is one possible explanation for your results. Again, I'm not certain
this is correct. However, if you notice a big drop in signal level well up
the HF spectrum when your network is installed, this would be plausible at
least.

-- Ross

I coupled it very loosely (2 1/2 turns) to
the coax near the RCVR and was astounded at the difference in reception.
Around 0500Z I logged 15 different aero beacons at between 260 and 420
khz ! The tuned circuit didn't bring the signal levels up...it took
the noise floor DOWN ! Same thing happened when I picked up a used
Barker & Williamson AT-300 Tee section tuner at a hamfest last weekend.
The peaks are not as pronounced as the longwave tank, but the 90 meter
band yielded a half dozen African stations where previously I'd heard
nothing but QRMN.
On some frequencies the most dramatic improvement came where the
peak in signal strength and the peak in noise came at slightly different
settings of the tuner. This to me is evidence that nearby noise sources,
even when filtered out of the detector and audio in the receiver are
still affecting the AGC line, turning down the effective signal. Seems
like an active preselector will help if you can't get an antenna out in
the clear, but even if you can, some more selectivity *before* the front
end of the receiver can help. I'm a convert.

I thought your choice of the word "stress" (above) was curious. I've
never seen that word used in the context of overloading a receiver's
front-end. I'm sure you know that signal overloading doesn't actually
damage anything in the radio, so what does "stress" mean to you in this
case? Just curious.

Stress, an in overall signal levels taxing the ability of one or more of the
linear amplification stages to remain in their linear regions.

Even a little bit of non-linearity allows spurious mixing products (e.g.
intermod) to occur.

Anythinng that knocks down the total signal level, especially if it's only
signals you don't want to listen to, will reduce that "stress".

Yes, it is a curious usage, but I'm just copying a usage I saw elsewhere wrt.
dynamic range.

-- Ross






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Ross Archer wrote:

"starman" wrote in message ...
Ross Archer wrote:

A disclaimer: I may be totally wrong about this, but I think what you built
is actually more like a sharp-tuned preselector than an antenna tuner,
because it's not resonating your antenna system or improving the impedance
mismatch, so much as it's favoring signals around the frequency of interest
over signals that are outside this range.

This would reduce the stress on your receiver's front end by attenuating
out-of-band signals. You can verify this (or disprove it) by comparing a
signal at say, 15 Mhz with and without your matching network installed. If
your HF signals drop in strength, this may explain why reception is so much
better with the parallel resonant circuit in place.

It's my understanding that a substantial antenna like yours will pick up
many volts of total RF at a very wide range of frequencies. These
components stress your front end, driving it into non-linearity and causing
mixing products, some of which will fall within the passband of the LF
signal you're trying to hear. This is experienced as a higher noise level.
The pre-selector knocks down these out-of-band signals, dramatically
reducing the amount of rmixing and thus reducing the background noise level.

I'm EXTREMELY skeptical of any claim that impedance matching by itself will
make any difference to HF reception once you have more than (say
arbitrarily) twenty feet of wire antenna, unless you're feeding a crystal
set. The reason why is, external noise is so high at HF that increasing
the efficiency of energy transfer increases the efficiency of noise transfer
just exactly as much as it increases the efficiency of signal transfer,
resulting in a net 0 dB change in signal-to-noise ratio. You get higher
S-meter readings, but no change in signal readability.

Preselection, on the other hand, should never hurt and would help in cases
where the receiver is overstressed by total signal levels.

This is one possible explanation for your results. Again, I'm not certain
this is correct. However, if you notice a big drop in signal level well up
the HF spectrum when your network is installed, this would be plausible at
least.

-- Ross


I thought your choice of the word "stress" (above) was curious. I've
never seen that word used in the context of overloading a receiver's
front-end. I'm sure you know that signal overloading doesn't actually
damage anything in the radio, so what does "stress" mean to you in this
case? Just curious.

Stress, an in overall signal levels taxing the ability of one or more of the
linear amplification stages to remain in their linear regions.

Even a little bit of non-linearity allows spurious mixing products (e.g.
intermod) to occur.

Anythinng that knocks down the total signal level, especially if it's only
signals you don't want to listen to, will reduce that "stress".

Yes, it is a curious usage, but I'm just copying a usage I saw elsewhere wrt.
dynamic range.

-- Ross

After reading your original post again, I see that you were using
'stress' to mean any signal level that causes the front-end of the
receiver to operate outside it's design limits, particularly with regard
to linearity.
I too am skeptical of the value of impedance matching or antenna tuning
if the receiver is already getting the signal levels it needs to operate
above the local noise floor. However one of the benefits of impedance
matching for certain antenna types like the inverted-L is you can also
achieve an effective RF ground for the coax shield when the matching
transformer (unun or balun) is located close to the ground. This allows
for a short (effective) ground connection from the common end of the
transformer windings to ground.


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"snip"

However one of the benefits of impedance
matching for certain antenna types like the inverted-L is you can also
achieve an effective RF ground for the coax shield when the matching
transformer (unun or balun) is located close to the ground. This allows
for a short (effective) ground connection from the common end of the
transformer windings to ground.

That would be a side benefit. The main reason for this grounding
arrangement is that the valley I live in gets wicked lightning storms. I
think that by having the entire antenna operating at DC ground with the
low resistance of the twin RG6 braids entirely outdoors and directly to
earth ground would reduce the possiblity of a direct lightning strike on
or near the antenna conducting enongh current past the grounded balun to
ignite the house where the leadin enters.

"starman" wrote in message
...
Ross Archer wrote:

"starman" wrote in message
...
Ross Archer wrote:

A disclaimer: I may be totally wrong about this, but I think what
you built
is actually more like a sharp-tuned preselector than an antenna
tuner,
because it's not resonating your antenna system or improving the
impedance
mismatch, so much as it's favoring signals around the frequency of
interest
over signals that are outside this range.

This would reduce the stress on your receiver's front end by
attenuating
out-of-band signals. You can verify this (or disprove it) by
comparing a
signal at say, 15 Mhz with and without your matching network
installed. If
your HF signals drop in strength, this may explain why reception is
so much
better with the parallel resonant circuit in place.

It's my understanding that a substantial antenna like yours will
pick up
many volts of total RF at a very wide range of frequencies. These
components stress your front end, driving it into non-linearity and
causing
mixing products, some of which will fall within the passband of the
LF
signal you're trying to hear. This is experienced as a higher noise
level.
The pre-selector knocks down these out-of-band signals, dramatically
reducing the amount of rmixing and thus reducing the background
noise level.

I'm EXTREMELY skeptical of any claim that impedance matching by
itself will
make any difference to HF reception once you have more than (say
arbitrarily) twenty feet of wire antenna, unless you're feeding a
crystal
set. The reason why is, external noise is so high at HF that
increasing
the efficiency of energy transfer increases the efficiency of noise
transfer
just exactly as much as it increases the efficiency of signal
transfer,
resulting in a net 0 dB change in signal-to-noise ratio. You get
higher
S-meter readings, but no change in signal readability.

Preselection, on the other hand, should never hurt and would help in
cases
where the receiver is overstressed by total signal levels.

This is one possible explanation for your results. Again, I'm not
certain
this is correct. However, if you notice a big drop in signal level
well up
the HF spectrum when your network is installed, this would be
plausible at
least.

-- Ross


I thought your choice of the word "stress" (above) was curious. I've
never seen that word used in the context of overloading a receiver's
front-end. I'm sure you know that signal overloading doesn't actually
damage anything in the radio, so what does "stress" mean to you in
this
case? Just curious.

Stress, an in overall signal levels taxing the ability of one or more of
the
linear amplification stages to remain in their linear regions.

Even a little bit of non-linearity allows spurious mixing products (e.g.
intermod) to occur.

Anythinng that knocks down the total signal level, especially if it's
only
signals you don't want to listen to, will reduce that "stress".

Yes, it is a curious usage, but I'm just copying a usage I saw elsewhere
wrt.
dynamic range.

-- Ross

After reading your original post again, I see that you were using
'stress' to mean any signal level that causes the front-end of the
receiver to operate outside it's design limits, particularly with regard
to linearity.
I too am skeptical of the value of impedance matching or antenna tuning
if the receiver is already getting the signal levels it needs to operate
above the local noise floor. However one of the benefits of impedance
matching for certain antenna types like the inverted-L is you can also
achieve an effective RF ground for the coax shield when the matching
transformer (unun or balun) is located close to the ground. This allows
for a short (effective) ground connection from the common end of the
transformer windings to ground.

And in my experiments, it's a major advantage in reducing local noise
pickup, when the coax shield is connected to a ground rod and into the
ground.

Just keep in mind that many impedance-matching tuners do not isolate RF
input and RF output from each other. They might not serve as well as a
transformer would in for noise pickup reduction?

-- Ross



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Ross Archer wrote:

"starman" wrote in message

After reading your original post again, I see that you were using
'stress' to mean any signal level that causes the front-end of the
receiver to operate outside it's design limits, particularly with regard
to linearity.
I too am skeptical of the value of impedance matching or antenna tuning
if the receiver is already getting the signal levels it needs to operate
above the local noise floor. However one of the benefits of impedance
matching for certain antenna types like the inverted-L is you can also
achieve an effective RF ground for the coax shield when the matching
transformer (unun or balun) is located close to the ground. This allows
for a short (effective) ground connection from the common end of the
transformer windings to ground.

And in my experiments, it's a major advantage in reducing local noise
pickup, when the coax shield is connected to a ground rod and into the
ground.

Just keep in mind that many impedance-matching tuners do not isolate RF
input and RF output from each other. They might not serve as well as a
transformer would in for noise pickup reduction?

Does Palomar's so called 'Magnetic Longwire Balun' isolate the RF input
and output? It may be an auto-transformer design with a low impedance
tapped secondary.


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