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Re: Topband: Newbie question

To: Mark Lunday <>
Subject: Re: Topband: Newbie question
Date: Mon, 23 Aug 2010 06:37:24 -0600
List-post: <">>

You might have two issues: The MFJ-259 being overloaded and a broken tuner.

a NEC models shows the 80 x 94 foot inverted-L having a feedpoint impedance
of 43 +j277 over perfect ground (1.8 MHz). As you say your modest radial
system will add 10-20 ohms. At 3.5 MHz NEC shows 117 -j592 ohms input

The MFJ can be overloaded and produce erroneous readings when there is
substantial receive voltage on the antenna. Do you have any nearby AM
broadcast stations? Do the readings change after 6 PM when AM BC stations
reduce output power? If so you might want to measure the VSWR using the SWR
meter in your transceiver.

The tuner used to tune the 80 x 52 foot inverted-L on both 160 and 80
meters. This tells us it has enough range to tune the various new antenna
configurations. An 80 x 65 foot inverted-L will be resonant at 1.8 MHz and
should present a VSWR of around 1.25:1 with your ground system. This antenna
can be used as a test of the antenna, the MFJ-259, and the tuner.

     Dave WX7G

On Sun, Aug 22, 2010 at 7:07 PM, Mark Lunday <> wrote:

> OK, Topbanders, I have a mystery I am trying to solve with my inverted L
> Last December, I put up ¼ inverted L (vertical was 80 feet, horiz was 52
> feet).  Remote coupler at the base (CG-3000 Pi-L).  It was cold outside and
> I was travelling a lot, so I only put down three radials…each 130 feet.  I
> wanted to see what would happen, establish a baseline from which I knew I
> could improve with more radials.
> I have 200 foot of low-loss coax from the shack, but I still don’t want to
> give up any of my 100 watts to SWR losses in the coax…so I use the remote
> coupler.
> Well, the results were astounding on 160 for my first attempt…45 countries
> with 100 watts, including lots of EU and a 4X at his sunrise.  I also heard
> and worked some excellent DX on 80 with it.
> In March, we had a horrific windstorm and the wire broke.  So I restrung
> it.
> Since putting it back up, I was unable to get the remote coupler to tune
> the
> inverted L on 160.  I tried changing the length of the wire to vary the
> resistance/capacitance to see if that would be more coupler-friendly.  I
> used lengths from 114 feet, 132 feet, and 174 feet.  No success.  I added
> four additional radials.  Still no tune with the remote coupler.
> So I decided to start a serious investigation.  Using an MFJ-259 tonight at
> the base of the antenna, I see 1 ohm of resistance and 400 ohms of
> reactance
> at 1.8 MHz, for a length of 174 feet of wire.   At 3.5 MHz, I see 25 ohms
> resistance and 85 ohms reactance.
> >From the readings, I have the following thoughts.
> *       I would expect a higher resistance with the longer wire above ¼
> wavelength on 160, say around 100 ohms, because an end-fed ½ wavelength
> wire
> should be seeing 5000 ohms.  Why the low resistance?
> *       I would expect a much higher resistance with the wire on 80 meters,
> maybe 500 ohms.  Not 5000, because it is NOT a half wavelength end-fed, but
> certainly higher than 25 ohms
> *       Even with just 6 radials, I should see 10 or 20 ohms of resistance
> on 160
> Any assistance/guidance appreciated.  I have time before 160 season starts,
> but I want to be READY!  Thanks in advance
> Mark Lunday
> _______________________________________________
> UR RST IS ... ... ..9 QSB QSB - hw? BK
UR RST IS ... ... ..9 QSB QSB - hw? BK

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