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From: MarkusVester@aol.com
Message-ID: <ce9.10f645f7.338a2a27@aol.com>
Date: Sat, 26 May 2007 20:26:15 EDT
To: rsgb_lf_group@blacksheep.org
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Subject: Re: LF: 500kHz ERP
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Hi John and LF,

having never transmitted and only sparadically monitored 500 kHz, I am a=20
little reluctant to state "outsider" opinions in the ongoing UK power limit=20
discussion. Anyway from a more technical perspective, I tend to very much su=
pport=20
Jim's views and favour an ERP based limit, if possible on the order of one t=
o=20
ten watts.

- Innovation: In my opinion, many of the new concepts for LF communication=20
have been centered around optimizing the receive side. FFT-based and coheren=
t=20
reception techniques are now widely employed by amateurs, which would not ha=
ve=20
been the case if signal strength was not so much limited. Unidirectional=20
receive antennas and noise cancellation approaches are being explored and us=
ed. On=20
the other side, maximizing antenna size is not a new art - large and efficie=
nt=20
antennas have been the standard method for broadcasting and commercial=20
communications.

- Equal opportunities: As Jim pointed out, a transmitter power based limit=20
would put many of us who have limited space available practically out of=20
business. This discrimination is probably more severe in the low and medium=20=
frequency=20
range, compared to HF where even a tiny or makeshift antenna can have=20
reasonable efficiency.

- Learning: It has been stated that the requirement of calibrating one's=20
antenna efficiency adds an additional burdon on the operator, compared to si=
mply=20
measuring TX power - agreed. On the other hand, I think this is a good thing=
:=20
having to learn these techniques, we are also led to understand a lot more o=
f=20
how an antenna works, and what the basic physical limits are.

- Compatibility and supervision: There is no way of measuring TX power from=20=
a=20
distance, and all potential spectrum compatibility issues in the far field=20
would have to be based on ERP assumptions anyway. Limiting transmitter power=
=20
would seem a bit like imposing a speed limit based on horse power rather tha=
n=20
miles per hour... However I have to concede that in close proximity of a sma=
ll=20
antenna driven by high power, significantly higher reactive nearfields will=20=
be=20
present, which may impose additional limits from electromagnetic compatibili=
ty=20
issues.

Best wishes to all
Markus, DF6NM


In einer eMail vom 24.05.2007 20:02:55 GMT-Normalzeit schreibt=20
james.moritz@btopenworld.com:=20

> Dear John, Rik, LF Group,
>=20
> I would agree with Rik's comments. Experimentation on 136k (and 73k) over
> the last several years has given us a pretty good idea of how to optimise
> the efficiency of small LF antennas, but it has also shown that, once "bes=
t
> practice" has been employed, one quickly reaches a point of diminishing
> returns where further improvements have negligible effect on the radiated
> signal level. Beyond this, significant improvement in antenna performance
> can only really be achieved by increasing the physical dimensions of the
> antenna, which is usually not feasible for non-technical reasons. The same
> is certainly true for 500kHz, although the antennas are effectively a bit
> better to begin with. So however much one may strive  to improve antenna
> efficiency, and whatever incentives there are, beyond a certain point it
> just isn't possible without discovery of some revolutionary and unknown ne=
w
> antenna design principle, which one cannot rely on ever happening (I
> hesitate to mention "Poynting vector synthesis"...). The 1W ERP limit on
> 136k has given us a fair amount of freedom and flexibility and has led to
> some interesting technical challenges and solutions (e.g. how to
> economically generate a lot of TX power and feed it into a tiny antenna
> without something going up in smoke :-) ) - I don't think the last several
> years on LF would have been nearly so rewarding if TX power had been limit=
ed
> to 10 or 20 watts as is currently being suggested for 500kHz.
>=20
> Cheers, Jim Moritz
> 73 de M0BMU
>=20
>=20

  =20

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Content-Type: text/html; charset="ISO-8859-1"
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<HTML><FONT FACE=3Darial,helvetica><HTML><FONT  SIZE=3D2 PTSIZE=3D10 FAMILY=
=3D"SANSSERIF" FACE=3D"Arial" LANG=3D"2">Hi John and LF,<BR>
<BR>
having never transmitted and only sparadically monitored 500 kHz, I am a lit=
tle reluctant to state "outsider" opinions in the ongoing UK power limit dis=
cussion. Anyway from a more technical perspective, I tend to very much suppo=
rt Jim's views and favour an ERP based limit, if possible on the order of on=
e to ten watts.<BR>
<BR>
- Innovation: In my opinion, many of the new concepts for LF communication h=
ave been centered around optimizing the receive side. FFT-based and coherent=
 reception techniques are now widely employed by amateurs, which would not h=
ave been the case if signal strength was not so much limited. Unidirectional=
 receive antennas and noise cancellation approaches are being explored and u=
sed. On the other side, maximizing antenna size is not a new art - large and=
 efficient antennas have been the standard method for broadcasting and comme=
rcial communications.<BR>
<BR>
- Equal opportunities: As Jim pointed out, a transmitter power based limit w=
ould put many of us who have limited space available practically out of busi=
ness. This discrimination is probably more severe in the low and medium freq=
uency range, compared to HF where even a tiny or makeshift antenna can have=20=
reasonable efficiency.<BR>
<BR>
- Learning: It has been stated that the requirement of calibrating one's ant=
enna efficiency adds an additional burdon on the operator, compared to simpl=
y measuring TX power - agreed. On the other hand, I think this is a good thi=
ng: having to learn these techniques, we are also led to understand a lot mo=
re of how an antenna works, and what the basic physical limits are.<BR>
<BR>
- Compatibility and supervision: There is no way of measuring TX power from=20=
a distance, and all potential spectrum compatibility issues in the far field=
 would have to be based on ERP assumptions anyway. Limiting transmitter powe=
r would seem a bit like imposing a speed limit based on horse power rather t=
han miles per hour... However I have to concede that in close proximity of a=
 small antenna driven by high power, significantly higher reactive nearfield=
s will be present, which may impose additional limits from electromagnetic c=
ompatibility issues.<BR>
<BR>
Best wishes to all<BR>
Markus, DF6NM<BR>
<BR>
<BR>
In einer eMail vom 24.05.2007 20:02:55 GMT-Normalzeit schreibt james.moritz@=
btopenworld.com: <BR>
<BR>
<BLOCKQUOTE TYPE=3DCITE style=3D"BORDER-LEFT: #0000ff 2px solid; MARGIN-LEFT=
: 5px; MARGIN-RIGHT: 0px; PADDING-LEFT: 5px">Dear John, Rik, LF Group,<BR>
<BR>
I would agree with Rik's comments. Experimentation on 136k (and 73k) over<BR=
>
the last several years has given us a pretty good idea of how to optimise<BR=
>
the efficiency of small LF antennas, but it has also shown that, once "best<=
BR>
practice" has been employed, one quickly reaches a point of diminishing<BR>
returns where further improvements have negligible effect on the radiated<BR=
>
signal level. Beyond this, significant improvement in antenna performance<BR=
>
can only really be achieved by increasing the physical dimensions of the<BR>
antenna, which is usually not feasible for non-technical reasons. The same<B=
R>
is certainly true for 500kHz, although the antennas are effectively a bit<BR=
>
better to begin with. So however much one may strive&nbsp; to improve antenn=
a<BR>
efficiency, and whatever incentives there are, beyond a certain point it<BR>
just isn't possible without discovery of some revolutionary and unknown new<=
BR>
antenna design principle, which one cannot rely on ever happening (I<BR>
hesitate to mention "Poynting vector synthesis"...). The 1W ERP limit on<BR>
136k has given us a fair amount of freedom and flexibility and has led to<BR=
>
some interesting technical challenges and solutions (e.g. how to<BR>
economically generate a lot of TX power and feed it into a tiny antenna<BR>
without something going up in smoke :-) ) - I don't think the last several<B=
R>
years on LF would have been nearly so rewarding if TX power had been limited=
<BR>
to 10 or 20 watts as is currently being suggested for 500kHz.<BR>
<BR>
Cheers, Jim Moritz<BR>
73 de M0BMU<BR>
<BR>
</BLOCKQUOTE><BR>
<BR>
</FONT>   </HTML>

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