"Antenna current is essentially constant during the transmission with
negligible tuning adjustments"
"Some little shift of phase and amplitude of the modes involved, altering
the interference pattern"

Yes

Consistent also with Alan's message, I believe.

73,  Jim AA5BW




-----Original Message-----
From: [email protected]
[mailto:[email protected]] On Behalf Of Paul Nicholson
Sent: Sunday, March 9, 2014 6:04 PM
To: [email protected]
Subject: Re: LF: Daytime 29.499 kHz

I'm pretty sure now this is a propagation change.

Info from Bob via PM indicates that the antenna current is essentially
constant during the transmission with negligible tuning adjustments.

I can think of no environmental factors around the tx that would affect
signal this much without affecting antenna current.

I'm doubtful that freezing ground over the NY land portion of the path would
have noticeable effect.  Skin depth is substantial at these frequencies,
tens of metres, maybe up to 100m or more, in dry rocky ground and down to 10
or fewer
metres in soggy wet soil.   This is the reflecting volume and
a thin frozen layer at the surface isn't going to make much difference to
it.

That leaves propagation then.  Some little shift of phase and amplitude of
the modes involved, altering the interference pattern.  We've seen on good
nights, occasional dips of the signal which indicate some competition
between modes during the night.  The outcome of that competition will vary
from one night to another.

We'll just have to be patient, it'll come back again.
There'll be times when WH2XBA/1 is coming in well and NAA
is low.   We could get a night that's really good.

Carrier tonight until 04:00.  Signal just now: 0.43 fT for 20 mins
which is strongest I've seen from Bob.   That'll make lines on
spectrograms if it keeps up!

--
Paul Nicholson
--