I have a groundplane antenna tuned at 125 MHz for the airband and a newly made QFH for NOAA POES. The QFH is inferior compared to my GP. It should be the other way around, that QFH should be a lot better than the GP. I have built according to plans, it is clockwize rotated and everything looks ok...... I use the same coax (switch antennas), but still, it won't work. Is there something I have missed??

Regards

Lasse

On Tue, 9 Oct 2012 12:33:16 -0700 (PDT), Lasse_radio
wrote:

I have a groundplane antenna tuned at 125 MHz for the airband
and a newly made QFH for NOAA POES. The QFH is inferior compared
to my GP. It should be the other way around, that QFH should
be a lot better than the GP.

True, for most parts of the sky, except for directly overhead where
the GP has a big null. You should get about 3dBi from both the GP and
QFH antennas. The difference is that the QFH will not have any cross
polarization losses, while the ground plane automatically has a -3dB
loss from the conversion from RHCP (NOAA-19???) to linear vertical
polarization.

I have built according to plans,
it is clockwize rotated and everything looks ok.....

According to what plans? Post the URL for the plans and a photo of
your construction, especially the phasing sections. If there's any
difference, someone will spot it.

I use the same coax (switch antennas), but still, it won't work.

Hopefully, you don't have both antennas connected at the same time.

Is there something I have missed??

Yep. What bird you're listening to, URL of construction article,
numerical measurements of signal strengths, methods of comparison,
mounting, lengths of coax cables, antenna pre-amp location, system
description, etc.

Deja Vu. The last time I troubleshot exactly such a system, I found
that the receiver supplied 5V bias for running an antenna mounted RF
amplifier. The QFH antenna appears as a short across the antenna
connector which clamped the 5VDC to ground, causing the pre-amp to act
comatose. Running the system on a bench test looked perfect because
the shorting antenna was disconnected. Adding a coaxial capacitor
isolator between the RF amp and the antenna connector fixed the
problem.

Hint: That what is mostly obviously correct, beyond any need of
checking, is usually the problem.

--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

On 10/10/2012 11:48 PM, Jeff Liebermann wrote:
On Tue, 9 Oct 2012 12:33:16 -0700 (PDT), Lasse_radio
wrote:

I have a groundplane antenna tuned at 125 MHz for the airband
and a newly made QFH for NOAA POES. The QFH is inferior compared
to my GP. It should be the other way around, that QFH should
be a lot better than the GP.

True, for most parts of the sky, except for directly overhead where
the GP has a big null. You should get about 3dBi from both the GP and
QFH antennas. The difference is that the QFH will not have any cross
polarization losses, while the ground plane automatically has a -3dB
loss from the conversion from RHCP (NOAA-19???) to linear vertical
polarization.

Excuse my pedantry, but -3dB loss is actually a 3db gain.

John