QFH antennas can burn pre amps


My QFH antenna seems to have a shortcut in it’s cables or connections. It burns two of my chinese preamps I connected to it :(. One weeks ago. One yesterday. I did’t know the antenna has a problem…

Now I have to wait another six weeks for getting two new preamps from china. And I should build a new QFH…


I cannot see any optical problem there…

Ouch. I had a chat with the developer of the LNA4ALL (9A4QV) a while ago, he suggested that these MMICs are quite sensitive to ESD;
he recommended antiparallell BAV99 diodes on the input to filter any high voltage discharges that could occur.

The preamps from uputronics also work fine in my setup for quite a while now. I guess they include such protection.

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The problem wasn’t ESD. The problem was my ** antenna. Both preamps burned up as I connected the same antenna to the preamps.

Never mind. Ordered two new PAs.

L’antenne QFH est une boucle fermée torsadée, soit pratiquement une résistance faible.
Rien de l’antenne ne peut griller un préampli, sauf l’électricité statique lié aux matériaux d’isolation ou de la foudre.
Il y a longtemps j’utilisais des LNA chinois, et j’en ai grillé aussi quelques-uns, c’était moi en manipulant l’antenne, qui ait produit de l’électricité static. J’ai mis des BAV99, problème résolu.
Deux BAV99 en tête-bêche à l’entrée du LNA comme le dite manawyrm, devrait protéger votre préampli.
J’utilise maintenant un LNA de chez Uputronics avec filtre 137 MHz depuis 2 ans et jamais de problème.

This would make sense if it was a power-amp and not a pre-amp and the antenna was connected to the output. It is probably static electricity picked up by the antenna.

@didierp09, this is an english speaking forum. Can you please write in english?


From Google Translate:
The QFH antenna is a twisted closed loop, practically a low resistance.
Nothing of the antenna can grill a preamp, except static electricity related to insulation materials or lightning.
A long time ago I used Chinese NAL, and I also roasted some, it was me by manipulating the antenna, which produced static electricity. I put BAV99, problem solved.
Two BAV99s head-to-tail at the entrance of the LNA as the so-called manawyrm, should protect your preamp.
I am now using a Uputronics LNA with 137 MHz filter for 2 years and never a problem.”