[Lowfer] 472-479 kHz

[pbunn]

Most of the antenna losses are dissapated in the ground or in resistive losses in the matching network. Only the power absorbed in the radiation resistance actually is transmitted.  In a short vertical antenna the Rr is a very small part of the resistance of the antenna. Most short verticals are worm burners


Pat
N4LTA

"Douglas D. Williams" <kb4oer at gmail.com> wrote:


On Tue, Sep 25, 2012 at 12:36 PM, 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.



Hi Craig. You are absolutely correct. Once the RF energy leaves the
antenna, it has to go somewhere. The problem is, most of the RF energy
input into an inefficient antenna is simply lost as heat.  JD and others
please correct me if I am wrong.



>  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.
>


Yes, that is true for HF.


>
> 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.
>


No. I disagree. Our military (and all military users of VLF/LF all over the
globe), take great pains to make their VLF/LF transmitting antennas as
efficient as possible, given the restrictions of their budgets, which are
vastly superior to all of ours put together, by a factor of (who
knows?....more than Bill Gates is worth) or more.



>
> 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.
>


Actually, I agree. A 25' vertical on 600 meters, given a clear space and
a good ground system has a very good chance of transmitting an excellent
signal, IMO, especially with our current weak signal modes.




>
> 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 was referring to the "small loop" for a receiving antenna, rather than a
transmitting antenna, although many "Lowfers" have successfully used loops
as transmitting antennas, but not as "small" as I am referring to, I.E. 3
meter diameter or less.


>
> 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
>
>
>

Good point. But still, up to a certain point, the smart money is spent
making the transmitting antenna more efficient. There does come a point of
diminishing returns, I concede, where the effort and finances are better
spent on pumping more power into whatever antenna you can reasonably
construct.
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