Trying to keep my post size down...
Ok, I see that isolated experience can be a problem. As far as I can see
there will be a level of complexity best averted by empirical testing, so
long as I don't miss something really fundamental. Which I am trying not to
do.. I found a USMC guide to RF and antenna selection, a 5MB PDF file, that
has a Marine's habit of cutting to the chase, it looks like I found a good
guide there.
http://www.armymars.net/ArmyMARS/Ant...antenna-hb.pdf

The topolgy I describe WILL carry imbalance through, I know. I thought it
might at least be a start if it didn't add any of its own. I realise you were
using the amps as an illustration of how imbalance can arise between those
toroids, I was thinking that fewer parts means less to go wrong. Precise
symmetry in topology might be a lot easier if I didn't have to use those.
Again, I wonder why they're even there. Isn't it easier to put a gain stage
after the second toroid?

Point taken on the costs of the selector. It was a long time ago, but I think
I saw something intended to do this task, a design that built it from wire
wound on a bit of plastic water pipe or something. I started Googling for
designs earlier but got waylaid. One bit of waylaying involved a remark that
tuning might offer more problems that a fixed narrowband filter, but so
little context was offered that I don't know how to judge the remark.

If I put up conspicuous loops here I might get people bothering me about
planning permission or some other means of negative compulsion. If I can
do this with a vertical whip it will be much less awkward.

On Mon, 04 Jan 2010 14:44:31 -0600, Lostgallifreyan
wrote:

Again, I wonder why they're even there. Isn't it easier to put a gain stage
after the second toroid?

A circuit serves more purposes than gain. Of course, the simple
circuitry found in the file we are discussing has limited offerings.
Of what is offered is controlling input and output Z which is not a
trivial matter.

My preference is found in using Operational Amplifiers instead of
discrete transistors. There is more design flexibility and more
purposes may be served. OpAmps will control input and output Z with
far more rigidity (it is very difficult for externalities to shift
these parameters making for a rock solid design). OpAmps will also
preserve fidelity (faithful phase, magnitude) and not introduce any
distortion, and will drive out noise not already in the signal. Other
advantages can be obtained, but this is enough.

If I put up conspicuous loops here I might get people bothering me about
planning permission or some other means of negative compulsion. If I can
do this with a vertical whip it will be much less awkward.

Practicality needs to be served too. Loops can be useful indoors as
well, and they needn't fill a room. They will test the limits of
balance with the nearby clutter - an opportunity to turn your
environment into an RF lab.

73's
Richard Clark, KB7QHC

Richard Clark wrote in
:

On Mon, 04 Jan 2010 14:44:31 -0600, Lostgallifreyan
wrote:

Again, I wonder why they're even there. Isn't it easier to put a gain
stage after the second toroid?

A circuit serves more purposes than gain. Of course, the simple
circuitry found in the file we are discussing has limited offerings.
Of what is offered is controlling input and output Z which is not a
trivial matter.

My preference is found in using Operational Amplifiers instead of
discrete transistors. There is more design flexibility and more
purposes may be served. OpAmps will control input and output Z with
far more rigidity (it is very difficult for externalities to shift
these parameters making for a rock solid design). OpAmps will also
preserve fidelity (faithful phase, magnitude) and not introduce any
distortion, and will drive out noise not already in the signal. Other
advantages can be obtained, but this is enough.


I really like op-amps too, they have often made my life easier. Not used them
in RF though, just audio and modest DC instrumentation designs of my own..

About those amps in that scheme, I think I didn't grasp what they were doing,
other than gain, because I assumed the idea of balancing implied by the
design would be central whether they were used or not. It still seems to me
that if the line worked without them, then a single stage could be applied
after the signal passed to the unbalanced input after the second toroid. If
not (as in not possible as opposed to merely awkward), then I'm still missing
something.

If I put up conspicuous loops here I might get people bothering me about
planning permission or some other means of negative compulsion. If I
can do this with a vertical whip it will be much less awkward.

Practicality needs to be served too. Loops can be useful indoors as
well, and they needn't fill a room. They will test the limits of
balance with the nearby clutter - an opportunity to turn your
environment into an RF lab.

73's
Richard Clark, KB7QHC


I'll definitely read up on loops. (Been reading the first of two USMC radio
handbooks today, second is an update of the one I found yesterday. No loops
mentioned in first, but the second is specific to antennas. Both guides are
quickly filling forgotten gaps in what I knew, plus showing me plenty I
didn't).

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.

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

Richard Clark wrote in
news
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.

Lostgallifreyan wrote in
:

Richard Clark wrote in
news
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.

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