On Sun, 14 Oct 2018 08:49:51 +0000, Spike
On 13/10/2018 20:43, Jeff Liebermann wrote:
I understand how antenna work and how to predict performance. I can
even do it without 4NEC2 or other antenna modeling program. For
example, the uglier the antenna, the better it works. Antennas that
are more expensive, bigger, and in violation of local building
ordinances, work the best. Experimental prototype antennas always
work while the production versions never seem to work as well. If
there are two ways to assemble an antenna, the wrong way will have
higher gain, lower VSWR, or both. High gain, small size, or wide
bandwidth; pick any two. Using these rules of thumb and others,
anyone can predict how well an antenna will perform by inspection and
without using computer models, Smith charts, or tedious calculations.
Thou shalt not abrev. What does WHS mean?
There has been much talk on UKRA in the recent past about the merits or
otherwise of various makes and models of VNAs. It's my view that the
point of having an Amateur licence is to be able to transmit signals
intended to be received by another station. One of the alleged virtues
of a VNA is to be able to set up one's aerial system. However, I
maintain that using cheap torch bulbs is an equally valid indicator of
the state of tune of one's station, and that a distant station cannot
tell the difference between a system set up with the aid of a VNA and
one set up with the aid of a torch bulb or two.
In a past life (1970's), I used to design marine radios and antennas.
At the time, my weapon of choice was the HP4815A vector impedance
No fancy display, no pretty graphs, no Smith chart display. Just
accurate numbers for the HF bands. I used it for everything that
needed impedance matching, including antennas. If you're thinking of
buying one, make sure that it includes the probe kit. It's useless
without the probe kit.
One of my ace technicians had a different way of doing RF. During the
day, he would use the best test equipment that the company could
afford. After hours, he would work on his own radios. However,
instead of using proper test equipment, he would literally tune for
maximum into a light bulb. I was disgusted, tried to help, but
failed. He insisted that a light bulb was "good enough". It took me
a while to decode what was happening.
Anyone can produce a workable antenna using primitive techniques. By
workable, I mean minimally functional and generally usable. For at
time, I was building matching networks for using an aluminum step
ladder as a VHF directional antenna. It worked, but improvements
beyond minimally functional were difficult.
So, why bother with all the fancy test equipment (VNA) if a light bulb
will do as well? Because with the fancy test equipment will squeeze
the last few decibels of performance out the antenna while the light
bulb is unlikely to do the same. If minimally acceptable is your
standard of excellence, then please continue using a light bulb for
tuning antennas. However, if you want to get all the performance
possible, then you'll need some fancy test equipment.
What was happening with my tech was that he did not want to expend the
time learning how to properly operate, understand, and analyze the
output from the fancy test equipment. While I consider this close to
sacrilege in a production environment, to someone just trying to get
his radio or antenna on the air, it's sufficient. If I light bulb got
him close enough to a working system, and didn't require any time to
study, it was "good enough".
Some of the local hams are very much into DX, contesting, and EME. To
be successful, one has to have a very efficient radio system with
everything optimized to the best possible performance. Everything has
to be optimized for the best possible performance. One can't do that
with a light bulb.
Since your view of ham radio is "to be able to transmit signals
intended to be received by another station", you don't need a VNA to
do that. An antenna tuner and a random length of wire will suffice.
However, if you plan to do more than that, some test equipment might
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558