[TowerTalk] Inverted Vee vs. Dipole QRN

K4SAV RadioIR at charter.net
Thu Nov 2 17:51:32 EST 2006


An inverted vee is not more susceptible to QRN than a dipole. There are 
two reasons the QRN is worse on 80 meters than 40 meters. 1. Noise level 
is much higher on 80 than 40. 2. You have a two element on 40 that 
provides a narrower beamwidth than an inverted vee. Additional gain 
increases both signal and noise, but the narrower beamwidth captures 
less noise relative to the signal level.

Your S meter reading of noise should drop when you go to a narrower 
filter, assuming the noise is random (or gausian). If it doesn't maybe 
you have the AGC set to slow and there is some impulse noise that is 
causing it to hang on the peaks.  Try changing the AGC to fast and see 
what you get. Also try the noise blanker. If you want to see if part of 
that noise is due to power line noise, try booting one of those PSK31 
programs and look at the waterfall. The lines generated by 60 Hz noise 
and its harmonics will stand out as vertical lines.

Jerry, K4SAV

Kelly Johnson wrote:

>Is an Inverted Vee inherently more susceptible to QRN than a dipole or yagi?
>
>My noise levels on 80m are much, much higher than my noise levels on
>40m.  I mean on the order of 6 or 7 S units higher.  I'm looking for
>an explanation.  I have a 2 element yagi on 40m, but an inverted vee
>on 80m.  Is it explainable by the vertical polarization of the
>inverted vee?  Is it just 80m vs 40m?  Is it the location of my
>inverted vee (ie.closer to the overhead power lines)?
>
>While I'm at it, how about an explanation of why the noise level on CW
>(with a 250Hz or 500Hz filter in line) is lower than SSB (with a
>2.4KHz filter in line) on 40m, but not on 80m.  It seems as if my S
>meter reads about S1 on a good day on 40CW and about S5 on 40SSB, but
>reads about S7 on 80CW and S8 on 75SSB.  I would expect noise levels
>on the S meter to drop when I kick in the 500Hz filter, but it doesn't
>seem to do so on 80 meters.  Could this just be a wacky S meter?  BTW,
>I'm using an FT-1000MP
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