Sangean ATS-909 external antenna impedance??
 

On Tue, 05 Jan 2010 11:54:23 -0600, Lostgallifreyan
wrote:

Btw, how critical is the resistance of wire in a few ground radials? I have
some thin stainless steel wire that would be strong and enduring out there
but at around 1.5 ohms or more per 6 inches I can't help thinking that's too
much. I like the idea though, because clamping ends of it very firmly between
copper washers could be fast and easy for good and reliable contact.

The stainless steel is a non-starter. Use more radials of wire-wrap
wire if you are concerned about visibility vs. thickness.
Vegetation/grass will quickly bury most wire when Spring comes (and
possibly before). Grass will be so tenacious that even mowing the
lawn will not bring it up (unless you have a thatching attachment).

73's
Richard Clark, KB7QHC

Sangean ATS-909 external antenna impedance??
 

Richard Clark wrote in
:

On Tue, 05 Jan 2010 11:54:23 -0600, Lostgallifreyan
wrote:

Btw, how critical is the resistance of wire in a few ground radials? I
have some thin stainless steel wire that would be strong and enduring
out there but at around 1.5 ohms or more per 6 inches I can't help
thinking that's too much. I like the idea though, because clamping ends
of it very firmly between copper washers could be fast and easy for good
and reliable contact.

The stainless steel is a non-starter. Use more radials of wire-wrap
wire if you are concerned about visibility vs. thickness.
Vegetation/grass will quickly bury most wire when Spring comes (and
possibly before). Grass will be so tenacious that even mowing the
lawn will not bring it up (unless you have a thatching attachment).

73's
Richard Clark, KB7QHC


Ok, copper's no problem, was just wondering about stuff I had plenty of at
hand.. I wish I had a lawn. :) I was thinking that it would be an ideal
method. My main difficulty (apart from a large amount of heavy logs (and most
of a tree trunk) is that the best place to mount the antenna is in a far
coner of a plot so I can't lay radials all round it. I can probably get the
permission of one neighbour to run a ground wire along the far end of his
garden along a low wall, but that same wall is a high wall on the other side,
there's a drop of several feet as well as no chance of permission to lay
wires there. This is why I'll want a ground rod, as a tree used to grow
there, the rotted roots might be my best chance of anything like a conductive
network that is close to the surface, in addition to a few ground wires. I'm
a tenant, I don't own the land, and can't do much except work round what is
there.

Sangean ATS-909 external antenna impedance??
 

Lostgallifreyan wrote in
:

Richard Clark wrote in
:

On Tue, 05 Jan 2010 11:54:23 -0600, Lostgallifreyan
wrote:

Btw, how critical is the resistance of wire in a few ground radials? I
have some thin stainless steel wire that would be strong and enduring
out there but at around 1.5 ohms or more per 6 inches I can't help
thinking that's too much. I like the idea though, because clamping ends
of it very firmly between copper washers could be fast and easy for
good and reliable contact.

The stainless steel is a non-starter. Use more radials of wire-wrap
wire if you are concerned about visibility vs. thickness.
Vegetation/grass will quickly bury most wire when Spring comes (and
possibly before). Grass will be so tenacious that even mowing the
lawn will not bring it up (unless you have a thatching attachment).

73's
Richard Clark, KB7QHC


Ok, copper's no problem, was just wondering about stuff I had plenty of
at hand.. I wish I had a lawn. :) I was thinking that it would be an
ideal method. My main difficulty (apart from a large amount of heavy
logs (and most of a tree trunk) is that the best place to mount the
antenna is in a far coner of a plot so I can't lay radials all round it.
I can probably get the permission of one neighbour to run a ground wire
along the far end of his garden along a low wall, but that same wall is
a high wall on the other side, there's a drop of several feet as well as
no chance of permission to lay wires there. This is why I'll want a
ground rod, as a tree used to grow there, the rotted roots might be my
best chance of anything like a conductive network that is close to the
surface, in addition to a few ground wires. I'm a tenant, I don't own
the land, and can't do much except work round what is there.


Thinking about what I read recently, it seems that if the whip is not
vertical but slightly leaning back over the plot of land toward the houses,
it will have a better chance of using the sky waves, but what I don't know is
whether that demands ground radials to be biased (if biased at all) to favour
coverage on the side the antenna is leaning over, or the other side. My guess
is the side it's leaning over... Is this true? If so, it will help a lot to
make the best of that space.

Sangean ATS-909 external antenna impedance??
 

On Tue, 05 Jan 2010 12:49:38 -0600, Lostgallifreyan
wrote:

Ok, copper's no problem, was just wondering about stuff I had plenty of
at hand.. I wish I had a lawn. :) I was thinking that it would be an
ideal method. My main difficulty (apart from a large amount of heavy
logs (and most of a tree trunk) is that the best place to mount the
antenna is in a far coner of a plot so I can't lay radials all round it.

Running a fan of 90 degrees is fine, there's nothing exact about this
except for those who imagine they will suffer the dB of
out-of-symmetry.

I can probably get the permission of one neighbour to run a ground wire
along the far end of his garden along a low wall, but that same wall is
a high wall on the other side, there's a drop of several feet as well as
no chance of permission to lay wires there.

Don't bother. It isn't worth anyone's effort or intrusion.

This is why I'll want a
ground rod, as a tree used to grow there, the rotted roots might be my
best chance of anything like a conductive network that is close to the
surface, in addition to a few ground wires.

A wire mesh or mat (like chicken coop wire) over the surface of that
area would serve far better. That doesn't sound like an option so the
matter of pursuing conductivity of rotted roots is an illusion.

I'm a tenant, I don't own
the land, and can't do much except work round what is there.

You'll be able to do enough without much impact.


Thinking about what I read recently, it seems that if the whip is not
vertical but slightly leaning back over the plot of land toward the houses,
it will have a better chance of using the sky waves, but what I don't know is
whether that demands ground radials to be biased (if biased at all) to favour
coverage on the side the antenna is leaning over, or the other side. My guess
is the side it's leaning over... Is this true? If so, it will help a lot to
make the best of that space.

Your gain/loss advantage will be in the direction from the antenna
base out along of the middle radial in a 90 degree fan. Leaning won't
significantly alter things for a very short antenna (in terms of
wavelength).

Now as to these advantages and disadvantages. Once you get to a
minimun set of radials (call it four), the addition of more wire won't
budge your S-Meter more than a needle width (and that is being
generous). The addition of more radials concerns establishing a firm
reference of ground for Z.

73's
Richard Clark, KB7QHC

Sangean ATS-909 external antenna impedance??
 

Richard Clark wrote in
:

On Tue, 05 Jan 2010 12:49:38 -0600, Lostgallifreyan
wrote:

Ok, copper's no problem, was just wondering about stuff I had plenty
of at hand.. I wish I had a lawn. :) I was thinking that it would be
an ideal method. My main difficulty (apart from a large amount of
heavy logs (and most of a tree trunk) is that the best place to mount
the antenna is in a far coner of a plot so I can't lay radials all
round it.

Running a fan of 90 degrees is fine, there's nothing exact about this
except for those who imagine they will suffer the dB of
out-of-symmetry.

I can probably get the permission of one neighbour to run a ground
wire along the far end of his garden along a low wall, but that same
wall is a high wall on the other side, there's a drop of several feet
as well as no chance of permission to lay wires there.

Don't bother. It isn't worth anyone's effort or intrusion.

This is why I'll want a
ground rod, as a tree used to grow there, the rotted roots might be my
best chance of anything like a conductive network that is close to the
surface, in addition to a few ground wires.

A wire mesh or mat (like chicken coop wire) over the surface of that
area would serve far better. That doesn't sound like an option so the
matter of pursuing conductivity of rotted roots is an illusion.

I'm a tenant, I don't own
the land, and can't do much except work round what is there.

You'll be able to do enough without much impact.


Thinking about what I read recently, it seems that if the whip is not
vertical but slightly leaning back over the plot of land toward the
houses, it will have a better chance of using the sky waves, but what I
don't know is whether that demands ground radials to be biased (if
biased at all) to favour coverage on the side the antenna is leaning
over, or the other side. My guess is the side it's leaning over... Is
this true? If so, it will help a lot to make the best of that space.

Your gain/loss advantage will be in the direction from the antenna
base out along of the middle radial in a 90 degree fan. Leaning won't
significantly alter things for a very short antenna (in terms of
wavelength).

Now as to these advantages and disadvantages. Once you get to a
minimun set of radials (call it four), the addition of more wire won't
budge your S-Meter more than a needle width (and that is being
generous). The addition of more radials concerns establishing a firm
reference of ground for Z.

73's
Richard Clark, KB7QHC


Thankyou. This is good, it sounds like the basic plan will work then, and I
might be able to get some chicken wire to cover at least part of it. One
possible complication I didn't mention is that the intended mounting point is
at a T junction of three wire mesh fences of equal height, about 6'. They
don't have very reliable conductivity between each zigzag strand (oriented
vertical) as at least one fence has a green plastic coating on its wires. I
intend mounting the whip on a concrete post at the junction of these fences.
I imagine the fences will raise (and make diffuse) the precise physical level
of the RF ground, but I don't know whether they'll be a serious problem, or
maybe even be helpful. I can try grounding them a bit better, but otherwise
there's not a lot I can do about them.

One other thought... In that USMC antenna manual there is a mention of
something similar, a 15' whip tilted and also tied back so the upper part is
almost horizonatal, it's intended as a way to use short(ish) distances for
skywave propagation. It looks useful given the context of trees and buildings
within 100m of my best mounting point. What I'm not sure of is whether the
curvature of their tied antenna is relevant, or a straight tilted whip would
have no significant differences.

Sangean ATS-909 external antenna impedance??
 

Lostgallifreyan wrote:

Thankyou. This is good, it sounds like the basic plan will work then, and I
might be able to get some chicken wire to cover at least part of it.

Chicken wire rusts out pretty fast.. You'd probably be better off just
scrounging some AWG20 copper wire and improvising a little grid or
randomly laying it out.


One
One other thought... In that USMC antenna manual there is a mention of
something similar, a 15' whip tilted and also tied back so the upper part is
almost horizonatal, it's intended as a way to use short(ish) distances for
skywave propagation. It looks useful given the context of trees and buildings
within 100m of my best mounting point. What I'm not sure of is whether the
curvature of their tied antenna is relevant, or a straight tilted whip would
have no significant differences.

Curvature isn't "significant", and for a lot of cases, the tilt isn't
either. But, tying the whip back does keep it from whacking too hard on
low hanging branches.

Sangean ATS-909 external antenna impedance??
 

On Wed, 06 Jan 2010 04:18:10 -0600, Lostgallifreyan
wrote:

Thankyou. This is good, it sounds like the basic plan will work then, and I
might be able to get some chicken wire to cover at least part of it.

There is a down-side to this and what you have revealed below:

One
possible complication I didn't mention is that the intended mounting point is
at a T junction of three wire mesh fences of equal height, about 6'. They
don't have very reliable conductivity between each zigzag strand (oriented
vertical) as at least one fence has a green plastic coating on its wires.

Both the mesh of chicken wire, and the fence crosspoints may suffer
from cross-modulation products due to corrosion at the joints AND if
the metal is galvanized. This is evidenced in a nearby transmitter
(and nearby is relative measure) exciting the wire, and rectifying at
the corroded crosspoints. This rectification creates harmonics and
you are off to the races in terms of spurious frequency generation
across a wide bandwidth.

Oh Brave New World of common mode.

I
intend mounting the whip on a concrete post at the junction of these fences.
I imagine the fences will raise (and make diffuse) the precise physical level
of the RF ground, but I don't know whether they'll be a serious problem, or
maybe even be helpful. I can try grounding them a bit better, but otherwise
there's not a lot I can do about them.

As you describe at least one fence having insulated wire (which is
good from the cross-mod point of view) this makes no difference RF
ground-wise; and being elevated only slightly shifts things.

One exception is found in proximity in that this elevated ground will
indirectly short out the lower section of your vertical. This is more
a matter of Z than sensitivity.

The solution is to elevate your vertical's feedpoint to the height of
the fence top.

One other thought... In that USMC antenna manual there is a mention of
something similar, a 15' whip tilted and also tied back so the upper part is
almost horizonatal, it's intended as a way to use short(ish) distances for
skywave propagation. It looks useful given the context of trees and buildings
within 100m of my best mounting point. What I'm not sure of is whether the
curvature of their tied antenna is relevant, or a straight tilted whip would
have no significant differences.

Well, what they (or you) call sky wave is properly NVIS (near vertical
incident _____ - I forget the last part) which is meant for local
communications, which is more what the ground forces are interested
in. The Marines in Afghanistan are not going to DX headquarters back
at Pennsylvania Avenue in DC. When I taught VHF/UHF comm in the Navy,
our equipement easily lost 10dB of transmitted/received signal levels
just getting from the shack to the antenna. We didn't care. Push
more power if necessary, as for reception, line of sight was all that
was necessary, and that was to the horizon (no more than 8 or 10
miles). I don't think the government has bought any QRP rigs since
WWII.

In fact, that tilting's mission has also been satisfied with end
loaded dipoles place directly on the ground (which was largely sand).
I and my buddy used one for field day. Another antenna is an
unterminated coax laid across the ground. Both suffer mightily in
efficiency, but they offer ease of construction and purport to enjoy
less noise problems. To this last, most local noise arrives by
vertical polarization, and signals in the sky arrive by elliptical
(both vertical and horizontal by varying degree) polarization. For a
quick and dirty test, I doubt any other test could be quicker to do.
You might want to add a short pig-tail to the unterminated coax.

Further experimentation would be to add 8 to 10 inches of ferrite
beads to the coax, half way back on it toward your shack. This would
snub your home's injection of noise into your receiver (conducting out
from the house on the coax outer shield and folding back at the far
end). The next experiment (if this first proved useful) would be to
add a local ground at the same point and tie it to the shield (after
penetrating the jacket, of course). Yes, this violates some of my
other advice about mixing grounds, but for experiment's sake, it will
add to your repertoire of learning the complexities and benefits of
ground. The purpose of this new ground is to discharge that choked
noise into ground. I have successfully done this to quiet my home's
noise generation as detected in my receivers. The ultimate proof of
this concept is being able to throw the master breaker on your home
and noting any change in the noise floor.

Throwing that breaker is probably at the extreme of your family's
tolerance of your hobby. To this end you want to plan to do it once.
This means doing a noise floor survey at hourly intervals for all
bands and keeping notes for a week or two. Then, one day when there's
the least possibility of disrupting domestic tranquility, throw the
main and do a quick survey again. I have managed to quiet my
receivers by 5 to 10 dB through tests like these.

Buried cable, or ground level run cable can snub local noise induction
too (but it is still a good idea to choke at the feed point if no
where else). This last observation is to inform you that metallic
connection to earth is not always necessary. You should be equally
informed that the proximity of earth can also negatively affect what
positive gains you are seeking too.

73's
Richard Clark, KB7QHC

Sangean ATS-909 external antenna impedance??
 

Jim Lux wrote in
:

Lostgallifreyan wrote:

Thankyou. This is good, it sounds like the basic plan will work then,
and I might be able to get some chicken wire to cover at least part of
it.

Chicken wire rusts out pretty fast.. You'd probably be better off just
scrounging some AWG20 copper wire and improvising a little grid or
randomly laying it out.


True. Was just thinking that it's not that hard to find something meshlike so
even if it did it could be replaced for free. Given the price of scrap
copper, that rarely comes free these days. :)

One other thought... In that USMC antenna manual there is a mention of
something similar, a 15' whip tilted and also tied back so the upper
part is almost horizonatal, it's intended as a way to use short(ish)
distances for skywave propagation. It looks useful given the context of
trees and buildings within 100m of my best mounting point. What I'm not
sure of is whether the curvature of their tied antenna is relevant, or
a straight tilted whip would have no significant differences.

Curvature isn't "significant", and for a lot of cases, the tilt isn't
either. But, tying the whip back does keep it from whacking too hard on
low hanging branches.


In the case of a 15' whip, tilt might be. At least, if it isn't I have to
wonder why that USMC antenna manual was suggesting one for short-range
skywave use.
Document is "MCRP 3-40.3c" (PDF) 'Figure 4-34. AN/MRC-138 with NVIS Antenna'.
(About 4/7 of the way through that file, as gauged by scrollbar).

Where I am it seems the best chance due to surrounding buildings, trees,
fences, etc, is to use a slightly less exaggeratedly steep 'view' of the sky
than is implied by that description and drawing. If you look at that drawing
you can see that it isn't done to tie the antenna out of the way. :) There
seems to be specific reason for doing what they do there.

The curvature made me wonder, based on a relector, in an indirect way... I
read that a longer straight isolated rod placed directly behind a whip,
separated by a quarter wavelength, could be a reflector. While I guess any
curvature in either that rod or the whip might be insignificant at low HF, I
inferred that it had to be straight to work efficiently if the whip was
straight. There seemed to be implications that straightness, or lack of it,
mattered. That made me wonder if curvature in a whip (forget the reflector, I
have...) leaning toward a building might very slightly favour pickup on the
convex side and attenuation on the concave side, or have any other mildly
directional benefits. If so it might be a useful part of a strategy to reduce
noise from nearby buildings. Of course it might be useless trying, but it
looks like a nice idea...

Sangean ATS-909 external antenna impedance??
 

Richard Clark wrote in
:

Well, what they (or you) call sky wave is properly NVIS (near vertical
incident _____ - I forget the last part)

Skywave. :) At least, according to the document I just mentioned in previous
post. Sorry, I'll get to the detail in your post now..

Sangean ATS-909 external antenna impedance??
 

Richard Clark wrote in
:

On Wed, 06 Jan 2010 04:18:10 -0600, Lostgallifreyan
wrote:

Thankyou. This is good, it sounds like the basic plan will work then,
and I might be able to get some chicken wire to cover at least part of
it.

There is a down-side to this and what you have revealed below:

One
possible complication I didn't mention is that the intended mounting
point is at a T junction of three wire mesh fences of equal height,
about 6'. They don't have very reliable conductivity between each zigzag
strand (oriented vertical) as at least one fence has a green plastic
coating on its wires.

Both the mesh of chicken wire, and the fence crosspoints may suffer
from cross-modulation products due to corrosion at the joints AND if
the metal is galvanized. This is evidenced in a nearby transmitter
(and nearby is relative measure) exciting the wire, and rectifying at
the corroded crosspoints. This rectification creates harmonics and
you are off to the races in terms of spurious frequency generation
across a wide bandwidth.

Oh Brave New World of common mode.


Hmm. :) Just going to have to chance that, the bigger fence (main road in T
junction metaphor) is a galvanised type, with plenty of weathering. If I have
patience I might weave in a grounded length of copper wire, but I suspect
more weathering will nullify any useful initial results of that move so I
probably won't.

I
intend mounting the whip on a concrete post at the junction of these
fences. I imagine the fences will raise (and make diffuse) the precise
physical level of the RF ground, but I don't know whether they'll be a
serious problem, or maybe even be helpful. I can try grounding them a
bit better, but otherwise there's not a lot I can do about them.

As you describe at least one fence having insulated wire (which is
good from the cross-mod point of view) this makes no difference RF
ground-wise; and being elevated only slightly shifts things.

One exception is found in proximity in that this elevated ground will
indirectly short out the lower section of your vertical. This is more
a matter of Z than sensitivity.

The solution is to elevate your vertical's feedpoint to the height of
the fence top.


Oh, it will be. A tad higher, if anything. Just a few inches though, between
bottom end of whip and top of fence.

One other thought... In that USMC antenna manual there is a mention of
something similar, a 15' whip tilted and also tied back so the upper
part is almost horizonatal, it's intended as a way to use short(ish)
distances for skywave propagation. It looks useful given the context of
trees and buildings within 100m of my best mounting point. What I'm not
sure of is whether the curvature of their tied antenna is relevant, or a
straight tilted whip would have no significant differences.

Well, what they (or you) call sky wave is properly NVIS (near vertical
incident _____ - I forget the last part) which is meant for local
communications, which is more what the ground forces are interested
in. The Marines in Afghanistan are not going to DX headquarters back
at Pennsylvania Avenue in DC. When I taught VHF/UHF comm in the Navy,
our equipement easily lost 10dB of transmitted/received signal levels
just getting from the shack to the antenna. We didn't care. Push
more power if necessary, as for reception, line of sight was all that
was necessary, and that was to the horizon (no more than 8 or 10
miles). I don't think the government has bought any QRP rigs since
WWII.


I don't have a lot of line of sight.. While I'm not living in a well, that
might be a closer analogy than the terrain most SWL'ers assume they'll find.
I do get a fair chunk of south and western sky though. I figured a scheme
intended to transmit to such a space should receive ok from it. If I try any
other angle I might as well try to hear the local neighbourhood noises, but
getting a sense of what lies beyond all that is why I'm doing this. Maybe
after some initial tries I might have to consider something much more
directional anyway, but hopefully not.

In fact, that tilting's mission has also been satisfied with end
loaded dipoles place directly on the ground (which was largely sand).
I and my buddy used one for field day. Another antenna is an
unterminated coax laid across the ground. Both suffer mightily in
efficiency, but they offer ease of construction and purport to enjoy
less noise problems. To this last, most local noise arrives by
vertical polarization, and signals in the sky arrive by elliptical
(both vertical and horizontal by varying degree) polarization. For a
quick and dirty test, I doubt any other test could be quicker to do.
You might want to add a short pig-tail to the unterminated coax.


An odd idea, but I like it. It might be that in my location some drastic
shifts from convention, to get best SNR never mind losses, then add gain
later, might be best. If something like that worked I'd leave it working.

Further experimentation would be to add 8 to 10 inches of ferrite
beads to the coax, half way back on it toward your shack. This would
snub your home's injection of noise into your receiver (conducting out
from the house on the coax outer shield and folding back at the far
end). The next experiment (if this first proved useful) would be to
add a local ground at the same point and tie it to the shield (after
penetrating the jacket, of course). Yes, this violates some of my
other advice about mixing grounds, but for experiment's sake, it will
add to your repertoire of learning the complexities and benefits of
ground. The purpose of this new ground is to discharge that choked
noise into ground. I have successfully done this to quiet my home's
noise generation as detected in my receivers. The ultimate proof of
this concept is being able to throw the master breaker on your home
and noting any change in the noise floor.

Throwing that breaker is probably at the extreme of your family's
tolerance of your hobby. To this end you want to plan to do it once.
This means doing a noise floor survey at hourly intervals for all
bands and keeping notes for a week or two. Then, one day when there's
the least possibility of disrupting domestic tranquility, throw the
main and do a quick survey again. I have managed to quiet my
receivers by 5 to 10 dB through tests like these.

Buried cable, or ground level run cable can snub local noise induction
too (but it is still a good idea to choke at the feed point if no
where else). This last observation is to inform you that metallic
connection to earth is not always necessary. You should be equally
informed that the proximity of earth can also negatively affect what
positive gains you are seeking too.

73's
Richard Clark, KB7QHC

Ok, I'll be keeping the feed line as mobile as I can, because I already
suspected that position and number of ferrite slugs might be something I want
to change a lot to test. Ultimately I hope I can run it along the top
of one of the chainlink fences. Circuit breakers will be no problem, I live
alone in a basement flat. :)