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<p><font face="Arial">Don't forget that a 1.4m whip on 30m will have
a Zo <<50 ohms and the closer the VSWR is to 1:1, without
utilising a matching network, the higher the system losses which
make it "look" like a good match. A 25 ohm antenna in a perfect
world will have a VSWR of 2:1 for 50 ohm coax.</font></p>
<p><font face="Arial">Old ARRL, et al, handbooks suggest resonating
the antenna with a GDO (I'm old school although mine uses a FET)
and then take care of the matching with a LC network. Having
said that, I've always tuned the antenna for VSWR and ignored
the losses. Scalar used to manufacture a HF antenna base that
contained a 2:1 transformer to improve efficiency. Did they
work? Haven't a clue.</font></p>
<p><font face="Arial">FWIW a base loaded antenna exhibits lower Zo
than one with the coil up higher. A centre-loaded whip with a
capacity hat used to feature in ham handbooks as a means to
improve efficiency. I've used both centre-loaded (no hat) and
continuously wound HF whips, and if there was a difference in
performance I didn't notice it.<br>
</font></p>
<p><font face="Arial">Ray vk2tv</font><br>
</p>
<br>
<div class="moz-cite-prefix">On 04/12/17 12:41, Glen English VK1XX
wrote:<br>
</div>
<blockquote type="cite"
cite="mid:3f843c2b-5c30-12b0-0461-d53a46b4112a@pacificmedia.com.au">BTW
everyone, if this is too off topic I can carry this privately. I
have experience with MF/LF antennas.....
<br>
<br>
HF30FX ahh yeah , right previous generation base loaded compared
to the centre loaded ones
<br>
<br>
yes, very much ground dependent. anything under 2:1 is probably
OK, with various ground arrangements see if there is a pronounced
dip anywhere
<br>
<br>
the sharper the dip, the more likely the efficiency is good .
<br>
<br>
My approach would be to ginore the VSWR once below 2:1 and try and
get the sharpest looking VSWR versus frequency curve
<br>
<br>
think of it this way :
<br>
<br>
If it was a dummy load, it would be good at all frequencies
<br>
<br>
if it was a high Q tuned circuit, then it would be good VSWR at
only one freq and infinite everywhere else
<br>
<br>
Your antenna will be somewhere in between a dummy load and a pure
tuned circuit...probably about 2:1 SWR BW of 50kHz (assume centre
matched to 1:1) indicates reasonable efficiency.
<br>
<br>
<br>
<br>
<br>
On 4/12/2017 12:13 PM, <a class="moz-txt-link-abbreviated" href="mailto:vk4tec@tech-software.net">vk4tec@tech-software.net</a> wrote:
<br>
<blockquote type="cite">Diamond HF30FX
<br>
<br>
<br>
<br>
-----Original Message-----
<br>
From: OZAPRS [<a class="moz-txt-link-freetext" href="mailto:ozaprs-bounces@aprs.net.au">mailto:ozaprs-bounces@aprs.net.au</a>] On Behalf Of
Glen English VK1XX
<br>
Sent: Monday, 4 December 2017 11:09 AM
<br>
To: <a class="moz-txt-link-abbreviated" href="mailto:ozaprs@aprs.net.au">ozaprs@aprs.net.au</a>
<br>
Subject: Re: [OZAPRS] Grounding of HF Antenna for APRS
<br>
<br>
well, there are alot of assumptions for pre cut antennas on
vehicles for HF.
<br>
<br>
So I wouldnt pay too much attention to SWR once it is below 2:1.
What sort is it ? WHat model / URL ?
<br>
<br>
<br>
On 4/12/2017 11:58 AM, <a class="moz-txt-link-abbreviated" href="mailto:vk4tec@tech-software.net">vk4tec@tech-software.net</a> wrote:
<br>
<blockquote type="cite">I went to see an engineer mate
<br>
<br>
He gave me some brass plate
<br>
<br>
I am cutting out a plate that will have a braid strap coming
off it
<br>
<br>
That should do the trick - he said the VSWR should come down
even further
<br>
<br>
Nudge bars are $1000
<br>
<br>
Andrew
<br>
<br>
-----Original Message-----
<br>
From: OZAPRS [<a class="moz-txt-link-freetext" href="mailto:ozaprs-bounces@aprs.net.au">mailto:ozaprs-bounces@aprs.net.au</a>] On Behalf Of
Glen English VK1XX
<br>
Sent: Monday, 4 December 2017 7:35 AM
<br>
To: <a class="moz-txt-link-abbreviated" href="mailto:ozaprs@aprs.net.au">ozaprs@aprs.net.au</a>
<br>
Subject: Re: [OZAPRS] Need a hand
<br>
<br>
yeah that will work. it would be out of the weather, and get
covered with oil/grease and probably weather seal it.
<br>
<br>
being close to the feedpoint actually isnt that necessary,
maybe no more than 1/20 of a wavelength, though , that is
probably a good number. so max strap length 1.5m for that
freq.
<br>
<br>
<br>
On 4/12/2017 8:27 AM, <a class="moz-txt-link-abbreviated" href="mailto:vk4tec@tech-software.net">vk4tec@tech-software.net</a> wrote:
<br>
<blockquote type="cite">Glen
<br>
<br>
I am thinking that maybe just a strap that fits in the gap
between the bonnet and the side wall.
<br>
<br>
I can sink a screw into the bonnet just inside
<br>
<br>
That way it would be as close to the feed point as possible
<br>
<br>
I would drill into the top side of the bonnet but that
equals a
<br>
divorce LOL
<br>
<br>
-----Original Message-----
<br>
From: OZAPRS [<a class="moz-txt-link-freetext" href="mailto:ozaprs-bounces@aprs.net.au">mailto:ozaprs-bounces@aprs.net.au</a>] On Behalf
Of Glen
<br>
English VK1XX
<br>
Sent: Monday, 4 December 2017 7:23 AM
<br>
To: <a class="moz-txt-link-abbreviated" href="mailto:ozaprs@aprs.net.au">ozaprs@aprs.net.au</a>
<br>
Subject: Re: [OZAPRS] Need a hand
<br>
<br>
In looking for a place to attach a ground strap, consider
that ideally, you want the largest continous area of metal.
That is probably the engine bay firewall (which would attach
to the upper body, roof etc) , fender mounts, or in the
rear, hinge mounts of the rear hatch, etc.
<br>
<br>
Anyone else have any input here on where to connect on a
modern vehicle to maximise surface area ?
<br>
<br>
comeon. ???
<br>
<br>
I am a bit out of tough on modern vehicles. (I have a 2005
XC90 which
<br>
if you pass a RG58 through a door seal will squash it flat
and cause a
<br>
short... hence requiring coax entry through a bung in the
spare tyre
<br>
well under the vehicle)
<br>
<br>
<br>
<br>
<br>
<br>
<br>
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</blockquote>
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