On 9 abr, 01:26, K7ITM wrote:
Hi Wim (and lurkers),

On Apr 8, 1:56 pm, Wimpie wrote:

On 8 abr, 18:52, K7ITM wrote:

...



I just ran EZNEC on a frequency-scaled version of the 14MHz 5 element
Yagi included in the sample files, with the D.E. slightly shortened to
allow a decent hairpin match to 200 ohms at the design center
frequency.

Did you also scale the thickness of the elements?

Yes, EZNEC lets you scale everything in the same proportion in one
quick operation.



I did a frequency sweep, 49 to 51 MHz, in 0.25MHz steps.

...

I don't know whether this will give sufficient BW improvement for the
Yagi as the Q is also determined by the reflector en directors. I am
looking forward to your simulation results.

Yes, of course. If the antenna itself is not wide-band, there is
rather little you can do about it. It may be possible with a more-or-
less complicated network to make the SWR bandwidth somewhat greater
(assuming still low loss--if you have a lossy network, you can make
the SWR bandwidth very large -- ;-) But making the SWR bandwidth
large does not make the antenna's gain bandwidth large. That is, for
a given set of directors and reflectors, the pattern will change with
frequency without much regard for what you do to get power into the
antenna.

Thanks for the encouragement about running some simulations. I'll
report results as I have a chance, probably this evening (US Pacific
coast time).

Cheers,
Tom

Hello Tom,

I do not have experience with EZNEC, so I didn't know that it also
scales element diameter.

Fully agree with regards to VSWR BW, gain BW and wide band dummy
loads....

Here it is UTC+2, so it is time for me te visit my bed for some hours.
Tommorow VAT administration is waiting.

Best regards,

Wim