Dave,
1) The doublet was fed with a short length of open-wire and correctly
matched through a Palstar balanced ATU.
2) The AGC on the receiver was OFF, and the RF GAIN backed off to
preserve linearity from RF through to audio.
3) Looking at the recording on an audio analyser suggests the long-term
average difference was around 6dB.
EZNEC modelling of the two antennas suggests the 6dB is coming from:
1) 1.5 dB "Free Space" gain of the HexBeam over the doublet (Hex is
about 3.5dBd and doublet is about 2dBd)
2) 3dB because the bearing to the US is about 20 degrees off the
direction of the Doublet's maximum lobe
3) 1.5dB due to better wave angle of the HexBeam
You might argue that 2) makes the comparison unfair to the Doublet, but
I would argue that I can rotate the HexBeam whereas I can't rotate the
Doublet :)
And let's not forget that Forward Gain is not the end of the story - the
beam's rejection of QRM from the rear and the side can be just as
important. Listen to the other audio clips and you'll hear 10-20dB F/B
performance from the HexBeam.
73,
Steve G3TXQ
WA3GIN wrote:
> Whats the input impedance? Is it matched? Do you suspect the wave
> angle of the two antennas is significantly different? How do you
> account for the significant difference in signal. For you to heard the
> difference at audio the RF signal has to be pretty significant to move
> the AGC around enough to be heard distinctly...youre talking 6db or
> more...its got to come from somewhere. I presumed the 132 antenna was
> attenuating at 20m due to input mismatch, if not then where is the
> gain coming from to make such a large difference to the listener's ear.
>
> 73,
> dave
> ----- Original Message ----- From: "Steve Hunt" <steve@karinya.net>
> To: <towertalk@contesting.com>
> Sent: Saturday, June 21, 2008 4:56 PM
> Subject: Re: [TowerTalk] G5RV vs. 2 element yagi
>
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