<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
</head>
<body>
<p>Hi Peter & everyone<br>
</p>
<p>Re the whip, short HF whips is a whole topic in itself! Yours
sounds like it is in an almost ideal situation. <br>
</p>
<p>If anyone is interested, I've attached a spreadsheet (Excel,
LibreOffice Calc) for calculating the required loading coil
inductance for a short (less than 1/4 wave) whip. It's based on a
method published in Ham Radio magazine many years ago. <br>
</p>
<p>The spreadsheet can be used with base loading, centre loading, or
combined base + centre loading. The last is useful for a portable
antenna where (for efficiency) you want most of the loading
somewhere in the middle of the whip but (for frequency agility)
you want to be able to tune the antenna near ground level using a
tapped coil. <br>
</p>
<p>The spreadsheet greatly reduces the amount of "cut and try", and
you can check out design choices before you build the antenna. It
deliberately slightly over-estimates the inductance, it is much
easier to remove coil turns than add them!</p>
<p>Instructions on how to use the spreadsheet are included in the
spreadsheet. <br>
</p>
<p>All the inductor does is tune the whip to resonance. It does not
bring the feedpoint impedance to 50 ohms. A good (efficient) 80 m
mobile whip should have a feedpoint impedance of only a few ohms
at resonance and will also require a matching system to match to
50 ohms. This can be a matching transformer or one of a variety
of matching networks. This is one situation where SWR can be
misleading - without a matching system, a good 80m mobile whip has
much higher SWR than a poor one! Tuning and matching are not the
same thing. <br>
</p>
<p>For any short antenna, generally the longer the better.
Radiation resistance is roughly proportional to the square of whip
length. If other losses stay about the same (and the dominant
loss is ground losses) then efficiency is also roughly
proportional to the length squared. Double the length = 4x the
radiated signal. It is instructive to try putting a few length
values into the spreadsheet and see what happens to the radiation
resistance. <br>
</p>
<p>Why is efficiency so important for a HF whip? Efficiencies of a
typical 80m whip range from abysmal (eg a popular multitapped whip
at very much less than 1%) to poor (even a very good 80m whip will
only be a few percent efficient). <br>
</p>
<p>Just to illustrate this point, I have measured more than 20 dB
difference in radiated signal between a reasonable 80m whip and a
poor one. That's over 3 'S' points. The measurement was done
with calibrated equipment. <br>
</p>
<p>Many operators are misled about whip performance by the apparent
ability to hear other stations on receive. On 80m, where the
receiver noise floor is way below band noise, even a 20dB
reduction in signal strength goes largely un-noticed on receive
but is very noticeable at the far end on transmit. So the ability
to hear stations on a mobile whip is not a good indicator of whip
performance. <br>
</p>
<p>Anyway, hope the spreadsheet is useful and gives some insight
into how short whips behave. <br>
</p>
<p><br>
</p>
<p>Cheers, John VK3ZRX<br>
</p>
<div class="moz-cite-prefix">On 04/07/2021 23:02, Peter Weeks Radio
wrote:<br>
</div>
<blockquote type="cite"
cite="mid:E94C360D-8113-4F81-8295-263562F8ABF1@weeksradio.com">
<meta http-equiv="content-type" content="text/html; charset=UTF-8">
<div>Hi Everyone,</div>
<div><br>
</div>
Thanks for the signal strength comparison chart John, it
certainly saved me looking it up.
<div><br>
</div>
<div>The antenna is mounted mid roof of my workshop roof being 20m
x 24m x 6m high and work much better with extended whip on 160,
80 & 40</div>
<div><br>
</div>
<div>Regards</div>
<div>Peter</div>
<div>VK3YZP<br>
<br>
<div dir="ltr">Sent from my Phone
<div><br>
<div><br>
</div>
</div>
</div>
<div dir="ltr"><br>
<blockquote type="cite">On 3 Jul 2021, at 19:44, John &
Bronwyn <a class="moz-txt-link-rfc2396E" href="mailto:jandbmorrissey@gmail.com"><jandbmorrissey@gmail.com></a> wrote:<br>
<br>
</blockquote>
</div>
<blockquote type="cite">
<div dir="ltr">
<meta http-equiv="content-type" content="text/html;
charset=UTF-8">
<p>Net opened at 20:30 hrs on 3600 kHz with VK3ZRX as Net
Control. <br>
</p>
<p>Checkins:</p>
<p>Mark VK3MDH /P Cobram, 59, reports lots of Vicpol
activity along the NSW / Vic border to do with Covid bans
on people entering Vic from any NSW 'red spot'. <br>
</p>
<p>Paul VK3FPDA, 57, reported poor sigs from everyone<br>
</p>
<p>Rik VK3EQ, 58, check in only, <br>
</p>
<p>John VK3MS Milawa, 59, working on getting his shack set
up & functional</p>
<p>Peter VK3YG Glenmaggie, 59, going interstate for a few
days, also celebrating 57th wedding anniversary. Congrats
Peter and Jen!</p>
<p>Peter VK3YZP Alexandra, 58, using a Codan radio with
tunable vertical (a Codan screwdriver with extended whip),
reported my sig as +14dBuV (see below)</p>
<p>All greatly saddened to hear of the passing of long-term
WICEN member Fred VK3JM. Vale Fred. <br>
</p>
<p>Coming events: <br>
</p>
<pre class="moz-quote-pre" wrap="">Saturday August 7th 2021
Gippsland Rally
Heyfield area
Contact: Ross Sargent VK3SF phone: 03 9736 4020
Email: <a class="moz-txt-link-abbreviated" href="mailto:vk3sf@outereast.com.au" moz-do-not-send="true">vk3sf@outereast.com.au</a>
Sunday August 15th 2021
Commanders & Co-Ordinators Meeting
ZOOM (TBC )
Contact: Ross Sargent VK3SF phone: 03 9736 4020
Email: <a class="moz-txt-link-abbreviated" href="mailto:vk3sf@outereast.com.au" moz-do-not-send="true">vk3sf@outereast.com.au</a></pre>
<p> Net control next week: Paul VK3DPW</p>
<p>Change of Net Control Roster: With Fred's passing and
another Net Control station not available for the
foreseeable future (due to other commitments), I think it
is time to revise the roster.</p>
<p>Anyone interested in being added to the net control
roster, please contact me. It is an interesting role and
a valuable skill to have! <br>
</p>
<p><br>
</p>
<p> And lastly, an explanation of Peter 3YZP's signal
report. The most common signal report is "S" units, with
(on HF) S9 defined as 50 uV at the antenna terminals.
Then each lower "S" number is half the signal strength
(-6dB) of the one just higher. Another common
specification is the actual signal strength in uV, most
radios are specified in this way for sensitivity. Then
there is dBm, which is the signal level in dB referred to
a signal level of 1 mW into 50 ohms (this is about 0.224
volts). <br>
</p>
<p>As well, some radios define signal levels in dB relative
to 1uV, with abbreviation dBu. <br>
</p>
<p> For comparison, here are the various "signal strength"
scales: <br>
</p>
<p> </p>
<table cellspacing="0" border="0">
<colgroup width="85" span="4"></colgroup> <tbody>
<tr>
<td height="17" align="center">'S’ Units (HF)</td>
<td align="center">uV</td>
<td align="center">dBu</td>
<td align="center">dBm</td>
</tr>
<tr>
<td height="17" align="center">9</td>
<td align="center">50</td>
<td align="center">34</td>
<td align="center">-73</td>
</tr>
<tr>
<td height="17" align="center">8</td>
<td align="center">25</td>
<td align="center">28</td>
<td align="center">-79</td>
</tr>
<tr>
<td height="17" align="center">7</td>
<td align="center">13</td>
<td align="center">22</td>
<td align="center">-85</td>
</tr>
<tr>
<td height="17" align="center">6</td>
<td align="center">6.3</td>
<td align="center">16</td>
<td align="center">-91</td>
</tr>
<tr>
<td height="17" align="center">5</td>
<td align="center">3.2</td>
<td align="center">10</td>
<td align="center">-97</td>
</tr>
<tr>
<td height="17" align="center">4</td>
<td align="center">1.6</td>
<td align="center">4</td>
<td align="center">-103</td>
</tr>
<tr>
<td height="17" align="center">3</td>
<td align="center">0.8</td>
<td align="center">-2</td>
<td align="center">-109</td>
</tr>
<tr>
<td height="17" align="center">2</td>
<td align="center">0.4</td>
<td align="center">-8</td>
<td align="center">-115</td>
</tr>
<tr>
<td height="17" align="center">1</td>
<td align="center">0.2</td>
<td align="center">-14</td>
<td align="center">-121</td>
</tr>
</tbody>
</table>
<p> </p>
<p>And just to confuse things further, there are actually
two "S unit" scales. On HF, S9 = 50 uV. But on V/UHF, S9
= 5 uV. This makes S1 on V/UHF = -141 dBm - pretty much
at the noise floor of a very good VHF/UHF receiver. So it
makes sense. And there are two dBu scales - the one above
which uses 1 uV, and another which uses 0.5 uV as the
reference, which is used by some Japanese manufacturers. <br>
</p>
<p>In practice the "S-unit" scales are nominal, not all
manufacturers follow the "S-unit" standard and even then,
radios often don't follow the scales accurately. <br>
</p>
<p>So my report from Peter of +14dBu was about S6. <br>
</p>
<p>Cheers, John VK3ZRX<br>
</p>
<p><br>
</p>
<span>_______________________________________________</span><br>
<span>wicenvic mailing list</span><br>
<span><a class="moz-txt-link-abbreviated" href="mailto:wicenvic@vic.wicen.org.au">wicenvic@vic.wicen.org.au</a></span><br>
<span><a class="moz-txt-link-freetext" href="http://vic.wicen.org.au/mailman/listinfo/wicenvic_vic.wicen.org.au">http://vic.wicen.org.au/mailman/listinfo/wicenvic_vic.wicen.org.au</a></span><br>
</div>
</blockquote>
</div>
</blockquote>
</body>
</html>