Antenna efficiency is significantly lower, no question. It is not going to be a walk in the park to make possible T/A crossings on a regular basis if at all. Time will certainly tell. I won't give up easily-Bob
> To:
[email protected]> From:
[email protected]> Date: Sat, 1 Mar 2014 21:15:16 -0500
> Subject: RE: LF: Re: U.S. VLF License WH2XBA
>
> So far as the less robust reception I got this afternoon here in the
> middle of the continent, there are a couple of other factors to
> consider in addition to propagation.
>
> Probably the biggest one is antenna efficiency. The frequency ratio
> from 74 kHz to 30 kHz is 2.46:1. Unless your antenna is significantly
> taller than for the other bands, that means the radiation resistance
> has diminished by the square of that ratio (a factor af about 6.08).
> At the very best, your loading coil loss and ground system resistance
> might remain about the same, but could very well increase (such as if
> the increased skin depth takes return currents lower into the earth,
> into a less conductive rock layer). So, I would expect overall antenna
> loss has increased significantly--perhaps by 15 or 16 dB.
>
> Second, I'm using the receiver outside its rated tuning range, by means
> of lower sideband mode. My 250 Hz IF filter helps minimize the static
> levels seen by the receiver, but seems to have a few dB additional loss
> when switched in the SSB chain. I discovered this a couple of months
> ago when I was testing various ways of copying your WSPR-2 signal at
> LF. Decoding was more effective when I used the narrow filter with
> upper sideband rather than the 1.8 kHz SSB filter, but was even _more_
> effective when the narrow filter was in the CW chain with its normal
> BFO offset. Therefore, my receiving setup is likely to be a few dB
> 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,
> it appeared that somewhat improved nighttime propagation might be
> kicking in. We'll know more in a couple of hours.
>
> John
>
> -----Original Message-----
> From: Bob Raide <
[email protected]>
> To: rsgb_lf_group <
[email protected]>
> 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
> better at 137 or even 74. Just got report from Kansas where I always
> put good daytime sigs in on 137-74. Got lot to learn about this VLF
> stuff-Bob
>
> - - - - -
>
> From:
[email protected]> To:
[email protected]> 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
> and night at LF and VLF the skywave is weaker in daytime at LF due to a
> portion of absorbing D-lyer below the apparent reflection height, also
> at VLF but less so. At the powers we use the ground wave probably does
> not go very far. I think the two are about the same strength at around
> 400miles then the skywave predominates. It may be less with amateir
> antennas because a lot more of the signal is lanuched at higher angles
> that would be the case for big antenna on Mil sites.
>
> I think there is some confusion about VLF being "all groundwave". Many
> of these ideas were formed in the days before Heaviside and Appleton.
> Ionospheric return is fom the D-layer in daytime (with some absorption)
> and by the lower E-layer at night.
>
> Paul Nicholson has front-ended some Mil propagtion software for VLF
> called LWPC you can tell its the "real stuff it was written in Fortran
> :-))
> Single shot strengths are calculated for the date and time entered so
> you can see diurnal effects. I have not tried it at very short range
> 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
>
>
>
>
>
