[Lowfer] 472-479 kHz

[pbunn]

The best is what was previously  stated. Put up the most efficient antenna that you can and power it to the legal limit.

I'm in the back yard now with a shovel sweating digging a foundation for the most efficient one I can build and I promise that building a transmitter is a lot more fun.

Pat
N4 LTA

craig wasson <craig at wasson.com> wrote:


That was kind of my point.  The RF energy has to go somewhere once it
leaves the antenna.  On 60M there is some advantage to having a
portion of the power go nearly straight up so a smaller antenna may
give more signal than a bigger one at some distances if you adjust
power to match the "gain" of the antenna.  It is sort of an equalizer
making mobile signals pretty much the same as base stations.

At 472 KHz its probably the groundwave you care about so maybe not an
issue.  But as long as the power goes out and is not absorbed by lossy
ground, nearby objects, etc an inefficient antenna is not necessarily
bad.   Since power is measured as radiated the key is to minimize
losses beyond the antenna, not within the antenna.  We'll not consider
the carbon footprint at this time.

I suppose a 10' antenna is a bad idea - but I see some pretty small
antennas on those AM roadside info transmitters at 540KHz.  I believe
there is a "standard" commercially available antenna I've seen online
for that use and I don't think it's more than 25' or so long with no
top hat.

Maybe the small loop would be a good choice since it's fairly
independent of ground and not as much affected by trees, etc.  Biggest
problem with the small loop was antenna losses from the high current,
but if you just care about radiated power it may work better than a
vertical with an imperfect ground as long as you compensate for losses
with more tx power.

I'm just making the point that up to now we've tried to squeeze every
last fraction of a watt from the transmitter due to working with a
straight power to the antenna rule.  With an ERP limit the rules are
different.  Maybe time to think outside the big top hats and extensive
grounds box?

Craig - N6IO


On 9/25/12, pbunn <pbunn at matrixei.com> wrote:
> My point is that power is cheap and efficient antennas are not and that it
> is cheaper to build a power amp than to greatly improve the antenna
> efficiency. For equal results - it is cheaper to go with power vs antenna
> efficiency.
>
> A ten foot antenna would be a very bad idea.
>
>
> Pat
>
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