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Indication of a no-contact antenna mount?


K5ZN 2021/04/30 08:16

Just installed a 10-meter NMO mount antenna on top of my van. No receive or transmit through it. Looking at the NanoVNA I don't know why it is so far off:

Can this readout be a symptom that the antenna is not contacting the NMO mount? It is a Larsen base and the antenna is Laird. That means instead of a bendable tang it has a spring-loaded center pin. Trouble is, I can't verify that the pin is contacting the NMO, but it may be close enough to measure the antenna's SWR. Any expertise on this?

-- K5ZN

Teton Amateur Radio 2021/04/30 09:37

First of all, I have always found NMO mounts to be the worst. If it
isn't bad now, it will be. What does it show with an ohmmeter??? That
would always be my first check.

Mick - W7CAT

----- Original Message -----
From: K5ZN
To: NanoVNAV2@groups.io
Sent: Friday, April 30, 2021 09:16:11 AM
Subject: [nanovnav2] Indication of a no-contact antenna mount?

> Just installed a 10-meter NMO mount antenna on top of my van. No
receive or transmit through it. Looking at the NanoVNA I don't know why
it is so far off:
>
> Can this readout be a symptom that the antenna is not contacting the
NMO mount? It is a Larsen base and the antenna is Laird. That means
instead of a bendable tang it has a spring-loaded center pin. Trouble
is, I can't verify that the pin is contacting the NMO, but it may be
close enough to measure the antenna's SWR. Any expertise on this?
>
> -- K5ZN
>
>
>
>
>
>
--
Untitled Document

David Eckhardt 2021/04/30 17:17

With the feedline connected to the NANO, lightly touch the antenna at the
tip. If the NANO display changes in a big way, the antenna is likely
properly connected to the NMO center. If very little change occurs when
touching the antenna tip, likely the antenna is not connecting to the NMO
center. Some of these antennas may have a tapped inductor between 'ground'
and the antenna, proper. This makes the ohm meter test unreliable.

Dave - WØLEV

On Fri, Apr 30, 2021 at 3:38 PM Teton Amateur Radio Repeater Association
(TARRA) <tarra@wyocat.com> wrote:

> First of all, I have always found NMO mounts to be the worst. If it isn't
> bad now, it will be. What does it show with an ohmmeter??? That would
> always be my first check.
> Mick - W7CAT
>
> ----- Original Message -----
> From: K5ZN
> To: NanoVNAV2@groups.io
> Sent: Friday, April 30, 2021 09:16:11 AM
> Subject: [nanovnav2] Indication of a no-contact antenna mount?
>
> > Just installed a 10-meter NMO mount antenna on top of my van. No receive
> or transmit through it. Looking at the NanoVNA I don't know why it is so
> far off:
> >
> > Can this readout be a symptom that the antenna is not contacting the NMO
> mount? It is a Larsen base and the antenna is Laird. That means instead of
> a bendable tang it has a spring-loaded center pin. Trouble is, I can't
> verify that the pin is contacting the NMO, but it may be close enough to
> measure the antenna's SWR. Any expertise on this?
> >
> > -- K5ZN
> >
> >
> >
> >
> >
> >
> --
>
>
>
>

--
*Dave - WØLEV*
*Just Let Darwin Work*

Teton Amateur Radio 2021/04/30 11:29

I would disagree with not using the ohmmeter check. A tapped inductor
makes no difference because it is above the connection. All you are
trying to do it confirm a connection.

Mick - W7CAT

----- Original Message -----
From: David Eckhardt
To: NanoVNAV2@groups.io
Sent: Friday, April 30, 2021 11:17:04 AM
Subject: Re: [nanovnav2] Indication of a no-contact antenna mount?

> With the feedline connected to the NANO, lightly touch the antenna at
the
> tip. If the NANO display changes in a big way, the antenna is likely
> properly connected to the NMO center. If very little change occurs when
> touching the antenna tip, likely the antenna is not connecting to the
NMO
> center. Some of these antennas may have a tapped inductor between
'ground'
> and the antenna, proper. This makes the ohm meter test unreliable.
>
> Dave - WØLEV
>
> On Fri, Apr 30, 2021 at 3:38 PM Teton Amateur Radio Repeater Association
> (TARRA) wrote:
>
> > First of all, I have always found NMO mounts to be the worst. If it
isn't
> > bad now, it will be. What does it show with an ohmmeter??? That would
> > always be my first check.
> > Mick - W7CAT
> >
> > ----- Original Message -----
> > From: K5ZN
> > To: NanoVNAV2@groups.io
> > Sent: Friday, April 30, 2021 09:16:11 AM
> > Subject: [nanovnav2] Indication of a no-contact antenna mount?
> >
> > > Just installed a 10-meter NMO mount antenna on top of my van. No
receive
> > or transmit through it. Looking at the NanoVNA I don't know why it
is so
> > far off:
> > >
> > > Can this readout be a symptom that the antenna is not contacting
the NMO
> > mount? It is a Larsen base and the antenna is Laird. That means
instead of
> > a bendable tang it has a spring-loaded center pin. Trouble is, I can't
> > verify that the pin is contacting the NMO, but it may be close
enough to
> > measure the antenna's SWR. Any expertise on this?
> > >
> > > -- K5ZN
> > >
> > >
> > >
> > >
> > >
> > >
> > --
> >
> >
> >
> >
>
> --
> *Dave - WØLEV*
> *Just Let Darwin Work*
>
>
>
>
>
>
--
Untitled Document

Terry Nixon 2021/04/30 14:07

Try a regular-type Antenna Analyzer like the MFJ or a Grid dip meter.
Check coax cable continuity to the NMO base, and also check the
cable center connector to shield for short circuit. They way things are
made today anything is possible!
WB0VQP- Terry in Iowa

On Fri, Apr 30, 2021 at 12:29 PM Teton Amateur Radio Repeater Association
(TARRA) <tarra@wyocat.com> wrote:

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