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Date: Mon, 03 Feb 2014 16:50:30 +0000
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Subject: Re: LF: DX VLF experiments in 3HD
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Hi,

I remember that some years ago I used to take part in "foxhunts" where=20
the Tx'ing station would transmit on a frequency in the 144Mhz band.=20
Once we were close enough, some of us used to switch to a 70 cms Rx and=20
antenna and home in using the harmonic and the greater directional=20
properties of the 79 cms yagi !!!
I guess this was the "Technology of the 'Spirit' rather than the=20
'letter' of the rules"

73
On 03/02/14 15:34, Stefan Sch=E4fer wrote:
> Hi Roger, VLF,
>
> Thanks for the discussion on the subject. There are different point of=20
> views and probably there will never be a common opinion. Hoever it is=20
> good to see the different point of views here.
> Please comment to the argumentation shown below:
>
> Well, about the " "feels" wrong", let us stay on the example of the=20
> QRO station TXing legal 750W in OP8 on 160m. Nothing is wrong with it,=20
> i think we can agree here (?). And a lambda/4 vertical antenna is used=20
> by many stations of course. This antenna is able to radiate the 3rd=20
> harmonic as well, anyway it isn't called a "frequency multiplier". *
> So what may be a typical 3rd harmonic supression in existing amateur=20
> radio equipments? Can someome make a guess?*
> My guess would be 40...50 dB. When it's *50 dB*, then it doesn't "feel=20
> wrong" for us. Anyway there are some mW ERP on the 3rd harmonic, even=20
> if we ignore it.
> Everyone of us can check it with his own equipment today.
> 750W - 50 dB is 7.5 mW. So obviously 7.5 mW on 53m (160/3) is legel as=20
> long as 750W is generated on 160m. This does not feel wrong, right? If=20
> we can agree here, then this is a good first step :-) *Do we?*
> -------
> Next step:
> If there are two stations, who are interested to study HF propagation=20
> on 53m, they can do it legally by transmitting on 160m. (same applies=20
> for LF or MF or VHF (e.g. 145 MHz =3D> 435 MHz!) of course). But they=20
> will quickly ask themselves "why do we have to waste so much power on=20
> a frequency that is of no interest for us and cause QRM for other=20
> stations on 160m?". So what can they do? Running the transmitter on=20
> 53m directly is not legal, but QRO is legal on 160m, with a few mW on=20
> 53m! Now, one of them has the idea to add an element which reduces the=20
> fundamental frequency (matching for the fundamantal frequency) so that=20
> the power on 160m becomes lower. Now if the power of the 3rd harmonic=20
> rises, they can reduce the transmitter power, so that the ERP of the=20
> 3rd harmonic is still the same as before. Now they have reduced the=20
> "QRM" for other 160m stations but the situation on 53m is still the=20
> same. Just the supression of the 3rd harmonic becomes lower (ratio=20
> 3f/1f), let's say it is 10 dB now. This means *40 dB* less power on=20
> 160m, i.e. 75mW, and still 7.5mW on 53m. Stations on 160m will be=20
> happy with this decision and nothing has changed on 53m. *Does this=20
> feel wrong now?*
> Your comments please.
> -------
> Now a next step for VLF:
> Imagine someone is transmitting on 5755 Hz, in combination with a=20
> neutral coupling element, a big ferrite transformer which has no=20
> narrow band matching to the antenna. There is no power limitation on=20
> VLF, so he can generate 10 kW on 5.755 kHz. Would this feel wrong then?
> We know 1:9 "baluns" or "magic baluns" for the HF bands which are=20
> doing the same! They are "matching" a high Z antenna to a low Z output=20
> of a transmitter and this is independent of the frequency, at least on=20
> HF. If the 3rd harmonic supression would be 50 dB again, then the=20
> power on 17265 Hz is 1 mW! As long as there are no interferences to=20
> other services, this does not feel wrong, or does it? And if so, why?=20
> Comments please! Thus i think the analogy is NOT "leaving your car=20
> across the exit from the local fire station" Or, explain which service=20
> is in analogy to the local fire station here??
> Next: The radiation resistance of an amateur antenna is much higher on=20
> 17265 Hz than on 5755 Hz, 9x higher! So there is a "gain" of 8 dB for=20
> the 3rd harmonic. Now, would you call a piece of wire a "frequency=20
> multiplier"?? That would feel wrong to me :-)
>
> 73, Stefan/DK7FC
>
>
> Am 03.02.2014 14:47, schrieb Roger Lapthorn:
>> Like many, I am more than a little concerned about the intentional=20
>> use of 3rd harmonic reception of a VLF signal. Although I cannot=20
>> really argue with Stefan's logic, somehow it jsut "feels" wrong.
>>
>> Very happy to hear of Stefan's 5kHz tests however. Good luck.
>>
>> 73s
>> Roger G3XBM
>>
>>
>> On 1 February 2014 16:46, Stefan Sch=E4fer=20
>> <Stefan.Schaefer@iup.uni-heidelberg.de=20
>> <mailto:Stefan.Schaefer@iup.uni-heidelberg.de>> wrote:
>>
>>     VLF,
>>
>>     This evening and night i'm planning to transmit on _*5.755 kHz*_,
>>     using the large antenna, the large coil and the large PA :-)
>>     I don't know what can be expected and how the system works at
>>     that frequency. Actually it is just _a first test for playing
>>     arround and doing some measurements_ :-)
>>     If some nearby stations want to give it a try, maybe even in
>>     *3HD*, then don't hesitate :-)
>>
>>     73, Stefan/DK7FC
>>
>>
>>
>>
>> --=20
>> http://g3xbm-qrp.blogspot.com/
>> http://www.g3xbm.co.uk
>> https://sites.google.com/site/sub9khz/
>> http://qss2.blogspot.com/
>> http://www.youtube.com/user/g3xbm <http://www.youtube.com/user/G3XBM>
>>

--=20
73 de pat g4gvw
qth felixstowe, uk
(east coast, county of suffolk)


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    Hi,<br>
    <br>
    I remember that some years ago I used to take part in "foxhunts"
    where the Tx'ing station would transmit on a frequency in the 144Mhz
    band. Once we were close enough, some of us used to switch to a 70
    cms Rx and antenna and home in using the harmonic and the greater
    directional properties of the 79 cms yagi !!!<br>
    I guess this was the "Technology of the 'Spirit' rather than the
    'letter' of the rules"<br>
    <br>
    73<br>
    <div class="moz-cite-prefix">On 03/02/14 15:34, Stefan Sch&auml;fer
      wrote:<br>
    </div>
    <blockquote cite="mid:52EFB70D.2000403@iup.uni-heidelberg.de"
      type="cite">
      <meta http-equiv="Context-Type" content="text/html;
        charset=ISO-8859-1">
      Hi Roger, VLF, <br>
      <br>
      Thanks for the discussion on the subject. There are different
      point of
      views and probably there will never be a common opinion. Hoever it
      is
      good to see the different point of views here.<br>
      Please comment to the argumentation shown below:<br>
      <br>
      Well, about the " "feels" wrong", let us stay on the example of
      the QRO
      station TXing legal 750W in OP8 on 160m. Nothing is wrong with it,
      i
      think we can agree here (?). And a lambda/4 vertical antenna is
      used by
      many stations of course. This antenna is able to radiate the 3rd
      harmonic as well, anyway it isn't called a "frequency multiplier".
      <b><br>
        So what may be a typical 3rd harmonic supression in existing
        amateur
        radio equipments? Can someome make a guess?</b> <br>
      My guess would be 40...50 dB. When it's <b>50 dB</b>, then it
      doesn't
      "feel wrong" for us. Anyway there are some mW ERP on the 3rd
      harmonic,
      even if we ignore it.<br>
      Everyone of us can check it with his own equipment today.<br>
      750W - 50 dB is 7.5 mW. So obviously 7.5 mW on 53m (160/3) is
      legel as
      long as 750W is generated on 160m. This does not feel wrong,
      right? If
      we can agree here, then this is a good first step :-) <b>Do we?</b><br>
      -------<br>
      Next step:<br>
      If there are two stations, who are interested to study HF
      propagation
      on 53m, they can do it legally by transmitting on 160m. (same
      applies
      for LF or MF or VHF (e.g. 145 MHz =&gt; 435 MHz!) of course). But
      they
      will quickly ask themselves "why do we have to waste so much power
      on a
      frequency that is of no interest for us and cause QRM for other
      stations on 160m?". So what can they do? Running the transmitter
      on 53m
      directly is not legal, but QRO is legal on 160m, with a few mW on
      53m!
      Now, one of them has the idea to add an element which reduces the
      fundamental frequency (matching for the fundamantal frequency) so
      that
      the power on 160m becomes lower. Now if the power of the 3rd
      harmonic
      rises, they can reduce the transmitter power, so that the ERP of
      the
      3rd harmonic is still the same as before. Now they have reduced
      the
      "QRM" for other 160m stations but the situation on 53m is still
      the
      same. Just the supression of the 3rd harmonic becomes lower (ratio
      3f/1f), let's say it is 10 dB now. This means <b>40 dB</b> less
      power
      on 160m, i.e. 75mW, and still 7.5mW on 53m. Stations on 160m will
      be
      happy with this decision and nothing has changed on 53m. <b>Does
        this
        feel wrong now?</b><br>
      Your comments please.<br>
      -------<br>
      Now a next step for VLF:<br>
      Imagine someone is transmitting on 5755 Hz, in combination with a
      neutral coupling element, a big ferrite transformer which has no
      narrow
      band matching to the antenna. There is no power limitation on VLF,
      so
      he can generate 10 kW on 5.755 kHz. Would this feel wrong then?<br>
      We know 1:9 "baluns" or "magic baluns" for the HF bands which are
      doing
      the same! They are "matching" a high Z antenna to a low Z output
      of a
      transmitter and this is independent of the frequency, at least on
      HF.
      If the 3rd harmonic supression would be 50 dB again, then the
      power on
      17265 Hz is 1 mW! As long as there are no interferences to other
      services, this does not feel wrong, or does it? And if so, why?
      Comments please! Thus i think the analogy is NOT "leaving your car
      across the exit from the local fire station" Or, explain which
      service
      is in analogy to the local fire station here??<br>
      Next: The radiation resistance of an amateur antenna is much
      higher on
      17265 Hz than on 5755 Hz, 9x higher! So there is a "gain" of 8 dB
      for
      the 3rd harmonic. Now, would you call a piece of wire a "frequency
      multiplier"?? That would feel wrong to me :-)<br>
      <br>
      73, Stefan/DK7FC<br>
      <br>
      <br>
      Am 03.02.2014 14:47, schrieb Roger Lapthorn:
      <blockquote
cite="mid:CAHAQVWM_QGdMUAc1Zmt31E1G8u_xpNOAao+Thb95TzjH3020jA@mail.gmail.com"
        type="cite">
        <div dir="ltr">
          <div>
            <div>
              <div>Like many, I am more than a little concerned about
                the
                intentional use of 3rd harmonic reception of a VLF
                signal. Although I
                cannot really argue with Stefan's logic, somehow it jsut
                "feels" wrong.<br>
                <br>
              </div>
              Very happy to hear of Stefan's 5kHz tests however. Good
              luck.<br>
              <br>
            </div>
            73s<br>
          </div>
          Roger G3XBM<br>
        </div>
        <div class="gmail_extra"><br>
          <br>
          <div class="gmail_quote">On 1 February 2014 16:46, Stefan
            Sch&auml;fer <span dir="ltr">&lt;<a moz-do-not-send="true"
                href="mailto:Stefan.Schaefer@iup.uni-heidelberg.de"
                target="_blank">Stefan.Schaefer@iup.uni-heidelberg.de</a>&gt;</span>
            wrote:<br>
            <blockquote class="gmail_quote">
              <div>
                VLF, <br>
                <br>
                This evening and night i'm planning to transmit on <u><b>5.755
                    kHz</b></u>,
                using
                the large antenna, the large coil and the large PA :-)<br>
                I don't know what can be expected and how the system
                works at that
                frequency. Actually it is just <u>a first test for
                  playing arround and
                  doing some measurements</u> :-) <br>
                If some nearby stations want to give it a try, maybe
                even in <b>3HD</b>,
                then
                don't hesitate :-)<br>
                <br>
                73, Stefan/DK7FC<br>
              </div>
            </blockquote>
          </div>
          <br>
          <br>
          <br>
          -- <br>
          <div dir="ltr"><a moz-do-not-send="true"
              href="http://g3xbm-qrp.blogspot.com/" target="_blank">http://g3xbm-qrp.blogspot.com/</a><br>
            <a moz-do-not-send="true" href="http://www.g3xbm.co.uk"
              target="_blank">http://www.g3xbm.co.uk</a><br>
            <a moz-do-not-send="true"
              href="https://sites.google.com/site/sub9khz/"
              target="_blank">https://sites.google.com/site/sub9khz/</a><br>
            <a moz-do-not-send="true" href="http://qss2.blogspot.com/"
              target="_blank">http://qss2.blogspot.com/</a><br>
            <a moz-do-not-send="true"
              href="http://www.youtube.com/user/G3XBM" target="_blank">http://www.youtube.com/user/g3xbm</a><br>
            <br>
          </div>
        </div>
      </blockquote>
    </blockquote>
    <br>
    <pre class="moz-signature" cols="72">-- 
73 de pat g4gvw
qth felixstowe, uk
(east coast, county of suffolk)</pre>
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