[Lowfer] efficiency of multiple antenna systems

[Steve Olney]

Now, now Stewart - don't be a naughty boy !    I see you are up to your old
tricks again :-)    A bit of sideways sliding from your original statement
again :-)   Just in case you've honestly had a lapse of memory - here it
is:-

"The good news is that performance could be outstanding.  If you have four
synchronous one-watt transmitters, and the antennas are sufficiently
spaced so that their ground and other loss resistances are effectively
independent, the combined far field strength will be four times greater,
the equivalent of one 16-watt Tx!  IMO, 50 to 100 foot spacing is
adequate."

Thats 6db for 4, or 3dB for 2 on my calculator, (unless you are factoring in
the exchange rate from Aussi to US dollars).   No discounting now ! :-)

>
> It's been known for a long time, that one can combine two relatively
> closely spaced LF antenna systems, and get an efficiency greater
> than that of either alone.
>

Yes, we all knew that (well most of us) - the question was (and still is)
whether you get a neat 3dB for two, 6dB for 4 as you stated.    If you want
to modify your original statement that I responded to - now would be a good
time to do it.

>
> Unfortunately, I've had a hard time convincing some folks on this ML.
>

Only of the 3dB gain.

And of course, you quietly downgraded your statement later to:-

"As a result, the combined system has *almost* 3 dB higher gain (less loss)
than a single antenna."

No statement of how much loss though - crucial point in the argument.

And still later:-

"so the far field will be
*almost* 3 dB greater."

Just how much is "almost" ?

>
> Luckily, I stumbled across some professional documentation of this
> effect.  The station happens to be our own WWVB!
>

Possibly relative luck :-)     Just who is Glenn Nelson :-)?

Seriously though (well - only half) - how the performance of a system which
only manages to get 65% efficiency, instead of the "everyready" theory's 70%
odd supports the "nearly 3dB" case mystifies me.      They were pretty
chuffed to get from 57.5% to 65% - they would have even been happier to get
70%.     That would have bought a few sandwiches from the power bill
savings!   Maybe, Stewart, you should show them where they went wrong :-)

Actually, really seriously - please give us actual examples of practical
applications using numbers for a typical LowFer installation - and not where
you start from a really cr*ppy antenna that no serious LowFer uses.    Start
from a good standard practice installation and show us how (using modelling
preferably - many hopeful ideas have gone up in smoke after good modelling)
that you can produce a better antenna by multiple radiators.     Of course
the total extent of both ground systems must be the same in each case
otherwise you are gaining efficiency by stealth.

BTW, I also "stumbled" across a reference to this idea in the ARRL Antenna
Book.     There is given an example of a 1.8Mhz system consisting of two 50
foot antennas spaced by 10 feet (now there's a coincidence, 1.8Mhz/10 foot
spacing - 180kHz/100 foot spacing - sound familiar? - mmm...).    There it
is stated that the ground currents are not coupled - just how this is
possible with two 50 foot radiators spaced 10 feet apart I cannot
understand.    Subsequent queries to the principals of this publication (I
will not name them as I haven't ask permission for quoting them) produced a
lot of caveats.    A summary of the responses so far from that direction is
that it is better to make a single radiator more efficient by itself by
providing an adequate ground-radial under it.

BBTW, plugging in the parameters for Rrad and an estimated Rmutual of 0.32
ohms into the ARRL formula gives 75% efficiency referenced against the north
antenna and 85% referenced against the south antenna for the WWVB dual
installation.    Neither the published efficiency of 65%, nor the
"everyready" prediction of 70% agrees with this (?).

Considering there is still fairly vigorous arguments about the relative
merits of what would appear to be a simple question of buried versus
elevated radials, I feel we have a little way to go yet before we can make
definitive statements like the 3dB for 2, 6dB for 4 statement.

Certainly whether in the end better efficiency for our LowFer antennas would
not be obtained from putting the metal into reducing the losses in a single
radiator remains to be disproven.

Anyway I am working on trying to understand how this works and as I stated
before - I must be wrong as I am out-numbered - trouble is I can't let go
until I understand it (sorry - DC batteries and resistors don't cut it for
me).     I have ordered Antennas by Kraus (I already have Antenna
Engineering Handbook by Jasik - actually R.C. Johnson - 3rd Edition).
BTW, that book talks about VLF antennas and details multiple masts but only
talks about the advantages of this in terms of redundancy - no mention of
increasing efficiency. Strange that such a significant technique is not even
mentioned.

ON4UN's Low-Band DXing book makes a passing mention to multiple radiators.
Strangely, again, in the plethora of vertical array designs where fractions
of a dB are discussed in great detail there is not one further mention
(except a sideways reference to Beverage receiving antennas ??) or
description of this technique.

I will continue digging until I find my way past the general hand-waving on
this subject to the truth of the matter or I become exhausted or I prod
someone into actually providing proper proof...

73s Steve VK2ZTO
(who often wishes he could not care about not understanding...)