Loft mounting an aerial

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Loft mounting an aerial

Postby bones13 » Fri Dec 28, 2018 2:17 pm

Hi I have been into scanning listening to mainly mil air for about 8 months. First with an old realistic pro 43 and now with the 125xlt which I’ve had for around 4 months. I’ve been using either a W881 or a home brew antenna in the loft. I have purchased a diamond d777 which is going to replace my home brew. My question is as follows. Will I be best to mount the d777 vertically? I have been told that it’s omnidirectional so it doesn’t matter and should get it up as high as possible and mount along the rafters at the angle of the pitch of the roof, or horizontal at the ridge if the roof which would be as high as possible. As I am new to this some opinions from some experienced people would be much appreciated. I know outside on a pole would be better, but this is not possible for me.
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Re: Loft mounting an aerial

Postby G4RMT » Fri Dec 28, 2018 2:36 pm

You MUST mount it vertically, as it's designed to be omnidirectional and vertically polarised. if you mount it at an angle to vertical, the performance drops off, and at horizontal, it will be rubbish at picking up vertically polarised signals, and even then, it will have a directional characteristic - best pickup at 90 degrees to the direction of the antenna. Sticking it up in the loft as vertical as you can.
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Re: Loft mounting an aerial

Postby Chris P » Fri Dec 28, 2018 2:39 pm

as airband (both mil and civilian) transmitters are vertically polarised your D777 should be mounted vertically if mounted horizontally it will no longer be omni directional and at best you will lose 3Db in all directions and at worst you will lose all signals completely . a vertical monopole antenna only has a circular(omnidirectional) response at rightangles to the antenna . its response in the plane of the antenna is almost zero ie off the end
Regards Chris aka G8FFF nipper or tazmin88
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Re: Loft mounting an aerial

Postby bones13 » Fri Dec 28, 2018 6:05 pm

Thanks G4RMT and Chris for your replies. Your advise is fully taken on board. I shall endeavour to install is vertical when it arrives. To be honest it did sound a bit odd. Thanks again. Regards Andy
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Re: Loft mounting an aerial

Postby m0lsx » Fri Dec 28, 2018 6:34 pm

Get your 125 with it's standard antenna fitted & find a reasonably strong & consistent signal. Now hold your radio horizontally, which will reduce most VHF/UHF signals by half (3dB.) Now slowly rotate the whole radio. When the base of the antenna is pointing at the transmitter you will find the signal is nulled, sometimes to the point of non existence. That is because an antenna does not receive on the base.
The above is a good way of DF'ing, (Direction Finding,) a transmitter.
The above is also a good way of reducing overload from a strong signal source if you are listening in a temporary location. As having your antenna horizontally may reduce the strength of every signal, but having the base of the antenna pointing at the overloading transmitter reduces that by the most.
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