[Lf] [Fwd: LF: Transatlantic]

[Andre' Kesteloot]

Dave Brown wrote:

> Tnx to John (KD4IDY) for the useful comment.
>
> My point was that given the normal constraints on an amateur antenna LF
> setup, bigger ain't necessarily better for verticals, when gunning for real
> DX (2000 km plus)  Even a 'large' amateur antenna will still be a small
> fraction of a wavelength at LF so will have significant high angle takeoff
> as well as it's more immediately obvious (and useful) ground wave component.
> Increasing the height will reduce the takeoff angle as you described, but is
> this necessarily a good thing for amateur LF DX work?
>
> Crossing the pond with amateur antennas will require some thinking outside
> the square and it may be that trying to  minimise the number of hops is not
> the best way to go? Sounds stupid? Yes !!
>
> But consider this.. what sort of NDB antenna is in use at Galveston, Texas?
> The GLS signal is heard quite regularly down here in ZL. OK, they run a bit
> more transmitter power (2 kW? I think) than the usual NDB but not
> significantly more than some LF amateur stations and I doubt the tx antenna
> configuration is much different to the usual top loaded vertical NDB setup.
> It will have significant high angle radiation which would normally be
> consided undesirable but I suspect is the main contributor to the signal we
> hear down here.
>
> A typical larger amateur vertical antenna will have to have more than just
> size to compete when it come to real LF DX, (2000 km plus). High efficiency
> is paramount and we all know the biggest loss factor by far in any vertical
> antenna system used for LF is the ground loss. Big towers with poor or even
> mediocre grounds will fail miserably. I can speak with experience on this
> having used  ex BC band tx masts in both situations for LF experimental
> transmissions. The one with the far better ground system gave an impressive
> improvment (2-3 'S' points at 2000 km) over that with the poor ground.  Got
> similar reports from locals( 300km) as well.
>
> Perhaps the most interesting thing to consider is the fact that for the last
> 8 or 9 years, the biggest  LF signal out of ZL has consistently been that of
> Bruce, ZL1WB. His antenna is quite extensive, but it is NOT vertical!  He
> has 3500 feet of wire strung across a gully in a roughly north-south
> direction and with a 40 watt transmitter gets excellent night-time reception
> reports in Eastern VK as well as all over ZL.   He almost certainly will
> have a good signal in many areas of the Pacific but there are no listeners
> there to confirm.(Yet! Maybe we need a few Dxpeditions- any volunteers for a
> Pacific Island LF listening 'holiday'!!)
>
> Another aspect that has been noted already is the problem of  LF reception
> with large antennas. Reception requires a useable sig/noise ratio, and large
> antennas usually don't perform that well at LF in this regard because of all
> the QRM and QRN that they tend to pick up. Working VK  a year or  two ago we
> had to forget all about reception on the big vertical. We could hear the
> signals but QRN/QRM made it virtually impossible to copy.  Static crashes
> and electric fence interference were literally pegging the 'S' meter.
> Switching to a smaller 'random wire' antenna gave R5 sigs with what appeared
> on an aural basis to be perhaps only an 'S' point drop in  signal level but
> very little QRN. End result- probably a 30 dB improvment in sig/noise. You
> can probably only begin to appreciate what this means when you have actually
> tried using a really big antenna for LF reception.
>
> So while 'bigger is better'  may be the catchcry for some I'll be surprised
> if they are the ones who actually make it across the pond first. My money
> will be on those who have efficient (not necessarily big) antennas, located
> close to or on, the respective coasts, that can as KD4IDY sez, really run
> the full gallon on transmit, are good operators, and  above all, are
> prepared to keep at it!
>
> 73
> Dave
> ZL3FJ