Power ?

Andre' Kesteloot akestelo@bellatlantic.net
Sun, 27 Jun 1999 16:27:52 -0400

w4dlz@arrl.net wrote:

> In the repair article on your transmitter you talk about 150 watts..Also I
> read about 200 watts pep but no more than 2 watts eirp or no more than 1
> watt erp..

Hello Frank,The FCC authorizes us to transmit with up to 1 watt ERP

> I figure I'll never hear 1 or 2 watts on lf unless I'm in your
> vicinity..but 100 to 200 watts would be worth trying to hear...

you would be surprised. European hams regularly achieve two-way QSOs of over
1,000 kilometers with 50 or 100 milliwatts ERP. Also on our web page, you can
read on details of our January 1999 expedition to Nags Head (N.C) from where
we heard several LowFers (1 watt RF output into their antennas)  from
Pennsylvania (see the AMRAD Newsletter for March-April 1999)

> So what power are you radiating or putting into the antenna...Does 1 watt
> erp on LF equate to 100 watts of rf..to the aerial...?

I would guess (and this is only a guess at this point, as we are still very
much in the learning phase) that 100 watts of RF power into our antenna
tuning-unit probably corresponds to 50 milliwatts of radiated power.

Hence, the trick is to:

a) produce more power (again, some British hams feed up to one kilowatt into
their antennas)   My own transmitter, almost completed, will put out 1/4
kilowatt at 136 kHz.

b) create more efficient antennas. This is particularly difficult at LF,
because the radiation resistance of our (always too short) antennas are in the
_milliohms_   :-(
Most people use Marconi antennas (inverted "T") but loops work very well too,
and are less influenced by the quality of the ground.

c) use better modulation schemes that CW, such as BPSK, allowing us to "dig
into the noise".  Incidentally, most people on LF these days do not "hear" the
signal, but use DSP boards and public-domain programs such as "Spectrogram 5"
to "see" the transmissions on their computer screens.

d) at the receiver end, we have found that apart from huge square loops (10
feet on the side), the best results were obtained by remotely-tuned e-field
probe antennas (see the AMRAD Newsletter for Jan-Feb 1999)

You will find a lot of information on this subject on our web page
and then click on LF .  There are links to the European web pages, and you
will find that the British, the Germans, the Italians and the Dutch are
particularly active and inventive.

Hope this helps,
Andre' N4ICK