Vertical vs Horizontal shootout part one
 

K7ITM wrote:
I fully agree with Roy's comment about the AGC-derived S-meter output.
As he says, the AGC characteristics are temperature dependent, and they
are also dependent on the particular set of active devices (and to some
extent the passives too) in the signal path.

If you have access to a spectrum analyzer, chances are decent that it
will have a well-calibrated amplitude readout. The one I use is
accurate in a relative sense to a fraction of a dB over more than an
80dB range, and would certainly be sensitive enough for antenna
comparisons. I suppose both those would be true of most modern
spectrum analyzers. In addition, some are quite good at determining
the total power in a specified frequency range, and if you can find
such a range with no signals, you can get a better reading on noise
than you're likely able to do with an S meter, or even a narrow band
spectral measurement.

One of the most complex and difficult parts of a spectrum analyzer to
design is the log amp which provides this stable and precisely
logarithmic response over a wide dynamic range. There's an incredible
amount of really ingenious work on the part of some extremely talented
engineers in those circuits. In relatively recent times, Barrie Gilbert
and his folks at Analog Devices have done some equally clever work in
the design of IC log amps. It's not a trivial task by any means.

Roy Lewallen, W7EL

Vertical vs Horizontal shootout part one
 

Of course, you could make a receiver with very nearly true logarithmic
response, by use of one of the excellent, wide dynamic range log amps
which are available these days. But however much you or I might like
one, the vast majority of amateurs couldn't care less about what their
S meter is really indicating, so they wouldn't pay the added cost for
it.

On top of that, most amateurs would consider a 6dB-per-S-unit meter to
be "dead", and would rather have it wiggle more.

Roy Lewallen, W7EL


So true, that last part! Well, I certainly understand the non-
linearity of the RX when comparing gain accross the entire HF spectrum.
I tend to limit my operations to top band and 75, so I hadn't considered
changes in Rx gain when moving down the band (or up, as some would have
it). Currently, when I do an Rx calibration, I just take some readings
on my "S" meter when injecting a signal in the bands of my concern. A
"list" of these readings for each band suffices, although I agree with
you that that is far more than most hams would bother with.


Ed , K7AAT

Vertical vs Horizontal shootout part one
 

On Mon, 06 Mar 2006 13:47:04 -0800, Roy Lewallen
wrote:

[snip]


Of course, you could make a receiver with very nearly true logarithmic
response, by use of one of the excellent, wide dynamic range log amps
which are available these days. But however much you or I might like
one, the vast majority of amateurs couldn't care less about what their S
meter is really indicating, so they wouldn't pay the added cost for it.

Bill Carver, W7AAZ, designed such a beast. "A High-Performance AGC/IF
Subsystem", QST, May 1996.

I actually have one of his boards about half constructed... one I
started in 1996. Gotta get back to that someday.

Vertical vs Horizontal shootout part one
 

"Ed" wrote:
The bottom line for the Rx, all it cares about since it doesn't know
what kind of antenna is feeding it, is the signal strength at the
input.... so I'd say a calibrated microvolt reading reflecting that
strength is not very meaningless at all.
___________

Received signal strength, whether in terms of relative S-units or the
measure of real incident fields, is at least as much the result of local
conditions as of the ERP of the transmission source on the path toward the
receiver, the frequency, and propagation conditions.

So the received signal strength indication, whether relative or "real,"
isn't a hugely significant indicator of any of these parameters.

RF

Vertical vs Horizontal shootout part one
 

On Mon, 06 Mar 2006 13:47:04 -0800, Roy Lewallen
wrote:

Ed wrote:

The bottom line for the Rx, all it cares about since it doesn't know
what kind of antenna is feeding it, is the signal strength at the
input.... so I'd say a calibrated microvolt reading reflecting that
strength is not very meaningless at all. Any changes in the antenna
system will of course change that, but the whole point of any antenna
work is to maximize the signal voltage to that rx input, so I'd think a
calibrated reading would be extremely useful over an S meter alone.

I'm afraid it might require more than simple calibration. The S-meter
typically just shows the AGC voltage. The AGC response is only
approximately logarithmic, and depends on the gain characteristics of
the various stages being controlled. Gain characteristics are commonly
very temperature sensitive, so any calibration scheme would have to take
that into account, as well as the common deviation from true logarithmic
response of the various stages. Calibration would also be different on
different bands, with and without preamplifier or attenuators, etc.

Of course, you could make a receiver with very nearly true logarithmic
response, by use of one of the excellent, wide dynamic range log amps
which are available these days. But however much you or I might like
one, the vast majority of amateurs couldn't care less about what their S
meter is really indicating, so they wouldn't pay the added cost for it.

On top of that, most amateurs would consider a 6dB-per-S-unit meter to
be "dead", and would rather have it wiggle more.

Roy Lewallen, W7EL


Back many years ago, and probably still today, many hams would turn
away from a receiver that had what they called a "scotch" S meter. To
them a receiver that read S 6 while another receiver only read S 4 on
the same signal "had to be much better". Manufacturers started making
receivers with more lively S meters.
Looking at some of the older receivers such as the Collins had much
more realistic S meters than most today.

The calibration points that Mike did on his receiver should be valid
for any band for his antenna comparisons. An actual signal strength
measurement is not required nor would it be valid between bands. All
that is really needed is the difference measurements between the two
antennas so his calibration between points on the meter scale will be
valid on any band.

A really nice instrument that would be good for signal strength
measurements is an old HP 3586C selective level meter. It covers from
around 100 hz to 32 Mhz and has a digital readout to 2 decimal places
in dbm signal strength. Hard to use with other than a steady signal
though.

73
Gary K4FMX

Vertical vs Horizontal shootout part one
 

Gary Schafer wrote:
. . .
The calibration points that Mike did on his receiver should be valid
for any band for his antenna comparisons. An actual signal strength
measurement is not required nor would it be valid between bands. All
that is really needed is the difference measurements between the two
antennas so his calibration between points on the meter scale will be
valid on any band.

I'm not sure I fully understand this. The difference from one S meter
division to another *is* likely to be different on different bands,
since it depends on the gain-vs-voltage characteristics of the
controlled stages which can vary with frequency. But I do agree that he
can make good comparative antenna measurements without good S meter
calibration, because he has a step attenuator. By simply setting the
attenuator so he gets the same S-meter reading on both antennas, S-meter
calibration is completely irrelevant -- the antenna gain difference is
the attenuator setting.

I find it useful, however, to be able to see the difference with
reasonable accuracy just by looking at my S meter. But that does require
calibration for the band in use.

. . .

Roy Lewallen, W7EL

Vertical vs Horizontal shootout part one
 

Roy, you appear to have mislaid your sense of humor. Hope you recover
it soon. ;o)
----
Reg.

Vertical vs Horizontal shootout part one
 

Owen Duffy wrote:
On Sun, 05 Mar 2006 19:29:12 -0500, Mike Coslo
wrote:

Based on another thread a few weeks back in which Horizontal dipoles
were being compared to Vertical antennas, and from a little chiding from
Roy, W7EL, I decided to do some testing on my own personal versions of
the two.


Mike, this sounds interesting.

Sorry for the delay getting back on-line...

My setup is:

Icom IC-761
Antenna 1 - Homebrew OCF dipole at ~ 50 feet.
Antenna 2 - Butternut HF6V -ground mounted and 18 radials on the ground.


Question, does the magnitude of feedline radiation from the OCF
(presumably predominantly vertical) significantly affect qualification
of it as a horizontal antenna?

There shouldn't be any feedline radiationn, this is oan antenna
running coax to a 4:1 balun at the feedpoint.

Another, are the antennas coupled significantly, eg is one within the
near field zone of the other? It is pretty hard to avoid in a
residential block on the low bands, and it will confuse the results
somewhat.

Almost certainly there is some interaction. It isn't a very big yard.

Part one of this experiment is to calibrate the S-meter. I found that
trying to calibrate the thing with on-air signals was a nuisance, and
probably wouldn't be as accurate, so I used a signal generator.

I started out with a +20 signal, then worked my way down.

+20 start
S9 -18 db
S8 -23 db
S7 -26 db
S6 -29 db
S5 -32 db
S4 -35 db
S3 -37 db
S2 -39 db
S1 -41 db

Not only is the shape of the scale an issue, but the granularity or
resolution, especially with LCD meters, or any meter where there are
discrete steps in the meter current (such as where a D/A converter
drives the meter movement).

If you want to move beyond S meters, you could try FSM
(www.vk1od.net/fsm) and organise some constant carriers at known
distances / radiation angles that you could make a series of
measurements of and produce summary statistics (median and inter
quartile range) for each antenna type.

All in all, I would have to say that the meter tracks very well from S8
to S4, and the only place that wasn't that great was from S9 to S8. But
considering the transient nature of the signals we are receiving, I
would have to day that the S-meter is of reasonably close accuracy.

With my newly calibrated S-meter I am ready to start looking at what the
two different antennas are doing for me. I have a coaxial switch to jump
back and forth between the two. My initial impressions are that there
are some surprises. The difference in noise levels varies by antenna by
band. On some bands the vertical is noisier, and on others it is the OCF
dipole. Especially intriguing is that on PSK mode, where I can see
several signals at one time, switching between antennas will attenuate
some signals, while other signals increase in strength. I think that my
vertical works better than I gave it credit for, but If I definitely
want *both* antennas.

I described a technique for assessing the relative performance of
mobile stations by having them transmit known constant carrier, each
station space about 200Hz and turning circles in a carpark near each
other, and to observe them at typical propagation distances with an
audio spectrum analyser, watching the relative strength of the
carriers.

Your PSK setup is affording you the same type of comparison, and
provides a ready (and recordable) assessment of the relative strength
of the stations under the two antenna scenarios. Be great if you could
orchestrate stations at known distances as part of an organised test.

I'll probably be doing the next best thing, which is to do a lookup of
the various callsigns as I see them.

The more I see of waterfall displays, the more I like them. I would love
to see one as standard on an HF rig.

- 73 de Mike KB3EIA -

Vertical vs Horizontal shootout part one
 

Reg Edwards wrote:
Roy says,
People who blindly assume the marks on their S-meters are 6 dB
apart
should take a good look at your calibration results.

=======================================

The calibration of S-meters, 3dB or 6dB per S-point, has nothing to do
with which antenna produces the stronger received signal. It is purely
a comparison. Just use the same meter throughout the tests.

It does allow me to make a stab at comparing those two antennas. As I
continue on this test, it would be nice to have something that has some
sort of calibration. Otherwise we might as well just go to say "works
great" or "doesn't work well for all measurements.

- 73 de Mike KB3EIA -

Vertical vs Horizontal shootout part one
 

Roy Lewallen wrote:
K7ITM wrote:
I fully agree with Roy's comment about the AGC-derived S-meter output.
As he says, the AGC characteristics are temperature dependent, and they
are also dependent on the particular set of active devices (and to some
extent the passives too) in the signal path.

If you have access to a spectrum analyzer, chances are decent that it
will have a well-calibrated amplitude readout. The one I use is
accurate in a relative sense to a fraction of a dB over more than an
80dB range, and would certainly be sensitive enough for antenna
comparisons. I suppose both those would be true of most modern
spectrum analyzers. In addition, some are quite good at determining
the total power in a specified frequency range, and if you can find
such a range with no signals, you can get a better reading on noise
than you're likely able to do with an S meter, or even a narrow band
spectral measurement.

One of the most complex and difficult parts of a spectrum analyzer to
design is the log amp which provides this stable and precisely
logarithmic response over a wide dynamic range. There's an incredible
amount of really ingenious work on the part of some extremely talented
engineers in those circuits. In relatively recent times, Barrie Gilbert
and his folks at Analog Devices have done some equally clever work in
the design of IC log amps. It's not a trivial task by any means.

And in this case, it really isn't necessary. I simply need some
baseline to start my readings from.

Already I have noticed that different stations come in at different
strengths - presumably on the basis of propagation differences. There
may be some differences over time scales of minutes also. All I need is
a meter that allows me to derive a signal strength difference from two
different antennas. There was a need to calibrate that.

Of course, I would *love* to have a decent analyzer!!

- 73 de Mike KB3EIA -