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From: JD <us66soft@aol.com>
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Date: Sat, 1 Mar 2014 21:15:16 -0500 (EST)
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Subject: RE: LF: Re: U.S. VLF License WH2XBA
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So far as the less robust reception I got this afternoon here in the=20
middle of the continent, there are a couple of other factors to=20
consider in addition to propagation.

Probably the biggest one is antenna efficiency.  The frequency ratio=20
 from 74 kHz to 30 kHz is 2.46:1.  Unless your antenna is significantly=20
taller than for the other bands, that means the radiation resistance=20
has diminished by the square of that ratio (a factor af about 6.08). =20
At the very best, your loading coil loss and ground system resistance=20
might remain about the same, but could very well increase (such as if=20
the increased skin depth takes return currents lower into the earth,=20
into a less conductive rock layer).  So, I would expect overall antenna=20
loss has increased significantly--perhaps by 15 or 16 dB.

Second, I'm using the receiver outside its rated tuning range, by means=20
of lower sideband mode.  My 250 Hz IF filter helps minimize the static=20
levels seen by the receiver, but seems to have a few dB additional loss=20
when switched in the SSB chain.  I discovered this a couple of months=20
ago when I was testing various ways of copying your WSPR-2 signal at=20
LF.  Decoding was more effective when I used the narrow filter with=20
upper sideband rather than the 1.8 kHz SSB filter, but was even _more_=20
effective when the narrow filter was in the CW chain with its normal=20
BFO offset.  Therefore, my receiving setup is likely to be a few dB=20
less sensitive as well when working in this non-standard fashion.

On the positive side, just before I returned to town to check e-mail,=20
it appeared that somewhat improved nighttime propagation might be=20
kicking in.  We'll know more in a couple of hours.

John

-----Original Message-----
From: Bob Raide <rjraide@hotmail.com>
To: rsgb_lf_group <rsgb_lf_group@blacksheep.org>
Sent: Sat, Mar 1, 2014 3:45 pm
Subject: RE: LF: Re: U.S. VLF License WH2XBA

Alan;
I am noticing exactly that-groundwave not that good at 29 kHz.  Much=20
better at 137 or even 74.  Just got report from Kansas where I always=20
put good daytime sigs in on 137-74.  Got lot to learn about this VLF=20
stuff-Bob

- - - - -

From: alan.melia@btinternet.com
To: rsgb_lf_group@blacksheep.org
Date: Sat, 1 Mar 2014 21:15:41 +0000
Subject: Re: LF: Re: U.S. VLF License WH2XBA

Hi Bob if you mean "skywave" or ionospheric returns? that occurs day=20
and night at LF and VLF the skywave is weaker in daytime at LF due to a=20
portion of absorbing D-lyer below the apparent reflection height, also=20
at VLF but less so. At the powers we use the ground wave probably does=20
not go very far. I think the two are about the same strength at around=20
400miles then the skywave predominates. It may be less with amateir=20
antennas because a lot more of the signal is lanuched at higher angles=20
that would be the case for big antenna on Mil sites.

I think there is some confusion about VLF being "all groundwave". Many=20
of these ideas were formed in the days before Heaviside and Appleton.=20
Ionospheric return is fom the D-layer in daytime (with some absorption)=20
and by the lower E-layer at night.

Paul Nicholson has front-ended some Mil propagtion software for VLF=20
called LWPC  you can tell its the "real stuff it was written in Fortran=20
:-))
Single shot strengths are calculated for the date and time entered so=20
you can see diurnal effects. I have not tried it at very short range=20
but it certainly models he day-night transition quite well
It is at http://abelian.org/lwpc/

Best Wishes for Good VLF DX
Alan
G3NYK