Dave,
Thank you for the inputs and interesting information.
In my past I organized and lead a field test of various
commercial and a home brew 40 meter ground mounted vertical
antennas. This was basically focused on the improvements
experienced when starting with no radials laid on the ground to
4 radials and then doubling each increment of that, up to 32
radials. The signal improvements with the
additional radials was like or better than, adding a KW
amplifier.
We built a full sized 40 meter ground plane for the
reference antenna. It was matched at the base for a 50¦¸
impedance and fed with about 10 watts from a transceiver.
The match was optimized for each antenna tested.
Related to your comment about using fiber
between the sites: Fiber was not feasible at this time for us,
so in order to remove the affects of any cables out to the
receive site some 7 or 8 wavelengths away, W4TNS built a battery
powered 40 meter to 3/4 meter (no AGC) upconverter. We tested it
to find it's best operating input levels for best linearity and
made sure to operate the tests within those limits.
We utilized a small 40 meter receiving loop on 40 meters and a 5
element transmit yagi on 3/4 meters to feed the resulting
signals back to a Tektronix 2710 SA ,via another 3/4 meter yagi.
Both yagis were stably mounted at about 10'. The accuuracies
were subject to +/ - 1db amplitude variations in the SA, but the
preparation, process and the excercize, provided an awesome and
informative time for the 15 or 16 participants.
The tests
also revealed there was very little difference in signal
strength between the full size vertical and? the
commercial multi-band antennas on 40 meters, even though
the loaded antennas were usually shorter and more
complex than the full sized simple ground plane.
We did not have time to check the higher bands.
We did check several 40 meter mobile antennas and found
them to be somewhat directional depending on the
mounting locations, but surprisingly effective.
We realized the setup was
subject to several other variations, but we felt the tests would
still be helpful and useful. It was a fun ham radio activity to
be a part of. All that were there related they learned a lot.
73, Ray, W4BYG
On 8/11/2022 10:00, Dr. David Kirkby,
Kirkby Microwave Ltd wrote:
On Wed, 10 Aug 2022 at 21:15, Ray, W4BYG <
w4byg@...>
wrote:
On
the thread "...Making a Q meter":
On 8/10/2022 15:42, Dr. David Kirkby, Kirkby Microwave Ltd
wrote:
> if you look at the description of the group
>
> /g/Test-Equipment-Design-Construction
In reviewing the listed subjects, I would like to query the
group on
relatively simple "Electric field strength" measurements.
If it can be measured it's on topic. I just
updated the list to exclude things like ghost detectors, but
otherwise, any measurement is on topic.?
Anyone have something to offer on the subject?
Ray, W4BYG
?
I did in a former job make field strength measurements
where the whole of a passenger plane was considered the
antenna - this was an expensive measurement to perform, as
the plane had to fly around a mountain for a few hours. We
used many tonnes of fuel as jet engines are inefficient at
low altitudes. ??????
Not wishing to discourage measurements, but the truth
is that modelling tools will be more accurate than
measurements in many cases.
Spectrum
analyzers are not particularly accurate measuring power.
If you look at the calibration instructions for a
professional spectrum analyzer, you will see that power
meters are used. A measuring receiver is a professional
tool for making power measurements at specific
frequencies. They are very expensive on the used market.
I have never looked, but I doubt that a spectrum
analyzer would be used when calibrating a measuring
receiver.?
A few random thoughts, on areas that others have not
discussed.
One of the things that has always concerned me about
antenna measurements is the influence of the cable and
support structure. This has got me wondering if the
detector should be a small battery powered device on the
antenna, which transmits the signal level by optical
fibre. The linearity of the detector is irrelevant, as
that can be measured separately on a bench. Optical fibre
is much lighter than any coax, so for small antennas,
which the mass of the antenna is a lot less than the coax,
this should allow smaller support structures.
A transmit antenna could have a small
battery powered oscillator.?
I recently set up two large metal plates and
applied AC from a signal generator to provide a known E
field from?
E = V / spacing
I only did this to prove a cheap Chinese
meter, which claimed to measure E and H from 20 Hz to 3.5
GHz was a piece of crap. I got a full refund via eBay, as
the seller would not pay the return carriage to China.?
?
Dave.?
--
Dr. David Kirkby,
Kirkby Microwave Ltd,
drkirkby@...
Telephone 01621-680100./ +44 1621 680100
Registered in England & Wales, company number 08914892.
Registered office:
Stokes Hall Lodge, Burnham Rd, Althorne, Chelmsford, Essex, CM3
6DT, United Kingdom
--
"If you want to build a strong house, I'll give you my engineer's number.
If you want to build a strong life, I'll introduce you to my carpenter."
Lebron and Heather Lackey
Ray, W4BYG