Re: Observations
- From: Art Unwin <ArthurUnwin@xxxxxxxxx>
- Date: Fri, 26 Sep 2008 09:15:20 -0700 (PDT)
On Sep 26, 10:52 am, "JB" <nos...@xxxxxxxxxxxx> wrote:
"Art Unwin" <ArthurUn...@xxxxxxxxx> wrote in message
news:67630994-e9b3-4b5d-8462-3a5123615e35@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
On Sep 26, 7:49 am, "Rectifier" <redgranite_2...@xxxxxxxxx> wrote:
"Art Unwin" <ArthurUn...@xxxxxxxxx> wrote in message
news:27a34116-78d4-45ec-8bf4-8e5273555f5c@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
When modelling antennas and also building them it is obvious that
maximum gain comes about when resistance aproaches zero. Soooooooo
common sence says that the best antenna gain comes about when the anti
resonant point can be easily fed, welllll thats how my antennas work.
Unfortunatelly, the antenna was resonant on top band
but with a very low resistance so I have to start all over again. The
noise level did increase by 7 S units where modelling showed 9 dbi
gain ! Maybe I should use two radiators instead of the single one. O
well, I have to make changes so the anti resonance point is available
at top band. David, IT IS a topsy turvy world
so I am not available to listenning to the wobbly heads on the radio.
Oh shame for shame
Art
Uh, resistance? Are you talking about DC resistance? What about impedence?
You also stated, "Unfortunatelly, the antenna was resonant on top band butsaying,
with a very low resistance so I have to start all over again" after
"maximum gain comes about when resistance aproaches zero." Which is it? Is
your low resistance good nor not?
I feed antennas with a resistive feads without reactance, when it
becomes an impedance I retune or should I say the radio retunes
the antenna to make it resistive
to make it resistive
OK Art. I hate to put it this way, but you really need to take a course or
two to get on the same page and be understood in these subjects. Even a few
nights with the ARRL Handbook may help bridge the gap.
For instance. With Lumped Constants, when inductive reactance and
capacitive reactance are equal, the circuit is in resonance. Any series
resistance in the circuit will become a significant load and result in loss.
In an antenna, there will be a characteristic impedance of the feed point..
Although it may include the loss resistance, other factors determine that
impedance. Since there are nodes of high and low impedance on the antenna,
the feed point may be modified or relocated for different impedance. Also
because of the nodes, there will be high and low currents along the antenna.
Where the current is high, the losses in the resistance will be greater and
most greatly affect the Q.
I do not have any lumped constants. Maxwell's laws do not include
lumped loads only
distributed loads and my antennas revolve solely around the laws of
Maxwell which
being based on equilibrium includes all four forces of the standard
model
I have no problem with your suggestion, it is that I am just to busy
at what I do.
True ,you can feed at any point but there are penalties with that
aproach which I don't want to mess with,
I prefer to have continual tuning or adjustment at the antenna. Just a
reminder but my design is not
focussed around a planar form that concentrates on inter coupling of
radiators .
Best regards no offence taken
Art
.
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