LNA placement

Adrian878

Member
Joined
Jul 12, 2020
Messages
26
Hi all,

I have got a LNA4ALL and a RTL SDR FM bandpass filter, Adam the maker of the LNA says it’s best to place it close to the antenna as possible, but would I be better attaching the LNA 1 meter away from the antenna and placing the FM bandpass and LNA in a aluminium box minimising noise into the antenna or am I waisting time?
The LNA is powered by the Airspy mini and antenna is a x50 diamond, all in the loft.

Thanks.
 

ArloG

Member
Joined
Feb 14, 2020
Messages
124
It's always a good idea to put an LNA as close to the antenna as you can. In practice I just stick mine at the radio because it's handy.
Depends on your cable losses. A meter or two away shouldn't matter. If you're up in the UHF frequencies you'll definitely want the LNA close.
Experiment. Look at signal strength of known weak xmitter with the amp at the antenna and again with a few feet of coax and see what you get.
Weatherproofing the components is always smart. Up here there's only one FM broadcast station so I found that a filter isn't really needed. If there are any images from it, they're not really an issue. But there is a 152 MHz pager freq. that is.
 

Ubbe

Member
Joined
Sep 8, 2006
Messages
5,745
Location
Stockholm, Sweden
Remember to attenuate the signal before it is feed into a receiver. Few receivers can handle a 20dB increase in signal level without loosing sensitivity or even go into intermodulation. Depending of receiver quality you could need 6-15dB attenuation. It's easiest to use a variable 0-20dB attenuator to really dial in the total system gain figure that gives the best reception of weak signals.

/Ubbe
 
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