[OZAPRS] Unclassified RE: Ozaprs Digest, Vol 17, Issue 16

[Fleck, Bob MR]

 Guys why so complicated, all this maths. In the good old days (GOD) a
vertical for 2m was 19 inches and you needed at least 3 radials about 20
inches. Droop them down about 45 degrees to get the Z up closer to 50
ohm and lower the angle of radiation at the same time

A 1/4 inch longer or shorter moves the resonant freq about a MHz

SWR meter, what's that? (joking)
I haven't used one of them for ages and none of my rigs have let their
smoke out yet.

Personally, If I was building a 2m antenna for home, I'd build a "Slim
Jim" maximum angle of radiation is at the horizon i.e.. 0 degrees, right
where you want it for VHF. A Slim Jim is kind of like a folded J pole. I
have built dozens of them using 1/2" aluminium tube (old VHF TV
antennas) for my mates and not a dud among them.

73 Bob VK2BYF

-----Original Message-----
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Behalf Of ozaprs-request at aprs.net.au
Sent: Monday, 15 January 2007 12:00
To: ozaprs at aprs.net.au
Subject: Ozaprs Digest, Vol 17, Issue 16

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Today's Topics:

   1. APRS Satellite user interface (Andrew Rich)
   2. Re: 2M 1/4 Wave antenna (Marcus B)


----------------------------------------------------------------------

Message: 1
Date: Mon, 15 Jan 2007 07:20:20 +1000
From: "Andrew Rich" <vk4tec at tech-software.net>
Subject: [OZAPRS] APRS Satellite user interface
To: "ozaprs" <ozaprs at aprs.net.au>,	"Aprssig"
<aprssig at lists.tapr.org>
Message-ID: <LGEKIKIAKJPNFGILGJBBAENIDFAA.vk4tec at tech-software.net>
Content-Type: text/plain;	charset="iso-8859-1"

Gudday,

Anybody graphing PCSAT, ANDE and RAFT telem ?

I have setup a sat panel, would like to graph data next, and have a
parameters panel as well.

Open to suggestions.

http://vk4tec.no-ip.org/sat_panel.htm

Check out "Satellite Status"
-----------------------------------------
Andrew Rich
Amateur radio callsign VK4TEC
email: vk4tec at tech-software.net
web: http://www.tech-software.net
Brisbane AUSTRALIA



------------------------------

Message: 2
Date: Mon, 15 Jan 2007 10:12:08 +1100
From: "Marcus B" <mrmabs at gmail.com>
Subject: Re: [OZAPRS] 2M 1/4 Wave antenna
To: "VK / ZL APRS Users" <ozaprs at aprs.net.au>
Message-ID:
	<27d9617b0701141512n600a8446reb4382798c84bd13 at mail.gmail.com>
Content-Type: text/plain; charset=ISO-8859-1; format=flowed

On 14/01/07, Damien Gardner Jnr <rendrag at rendrag.net> wrote:
> ----- Original Message -----
> From: "Andrew Rich" <vk4tec at tech-software.net>
> > Searched for ages on google, looking for a 1/4 wave vhf calculation 
> > for
> > 145.825 MHz
> > I remember that the 45 degree radials had to be a ratio longer or 
> > shorter than the vertical element.
> > 1/4 Wave antenna = 51.43 cm
>
> It's been years since I built a 1/4 wave antenna, and a mate has my 
> RSGB antenna book at the moment, but I always used to take 5% off the 
> calculated length of the antenna.. I think for a bit of impedance 
> matching, though it's been WAY too long to say for sure :) I do 
> remember that the radials were exactly 1/4 wave, and by adjusting the 
> down-angle on them, you could tune the 1/4 wave to more closely match 
> your 50 ohm coax..? (nominal on a 1/4 antenna is 37 ohm or something 
> iirc?)
>
> Google seems to actually be suprisingly thin on 1/4 wave antenna
info..
> Really gotta get my RSGB back :)

Yeah, I should look that up while I've got your RSGB book here

An exact 1/4 wave matches 36 Ohms, exactly half a dipole, and if I
remember correctly (it isn't in the RSGB handbook), freq / 72 (roughly
95% of a quaterwave) can be used without a large elaborate groundplane.

But back to the handbook, it says to make a 50 Ohm match, to make the
antenna length longer than usual, then get out the SWR meter, not very
scientific for the RSGB handbook, but it does make sense in a way.

> Cheers,
>
> Damien
> --
> Damien Gardner Jnr
> VK2TDG/VK2DGJ. Dip EE. StudIEAust
> Home: rendrag at rendrag.net -  http://www.rendrag.net/
> Play: vk2tdg at pinegap.net  -  http://pinegap.net/
> --
> We rode on the winds of the rising storm,
>   We ran to the sounds of thunder.
> We danced among the lightning bolts,
>   and tore the world asunder
>
>
> _______________________________________________
> Ozaprs mailing list
> Ozaprs at aprs.net.au
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>


--
VK3TST
-- "People aren't stupid. Usually." -- jd


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