146.5MHz rx threshold ?

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G4WIM
Posts: 109
Joined: Thu Jan 29, 2015 8:36 pm
Location: Freckleton, Lancs

146.5MHz rx threshold ?

Post by G4WIM » Sun Aug 13, 2017 2:44 pm

Just been doing some tests on my 146.5MHz rbw rx for GB3FT and with a 20dB gain 1.3dB NF pre-amp ahead of the MiniTiouner I measure a rx threshold of -111dBm at 333kSpS.

Wonder what others are measuring ?

Number seems about right.

With no signal Minitiouner indicates an RF power of -76dBm then with a signal at -111dBm it reads -67dBm gets a fast signal lock and an MER of 6dB.

73 Tim

M0DTS
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Re: 146.5MHz rx threshold ?

Post by M0DTS » Mon Aug 14, 2017 6:22 pm

I recall measuring -110dBm for 5dB MER 333kS 7/8 when i tested my Rx setup a couple of years back so it sounds good.
LNA was Microwave Modules one with around the same noise figure as you quoted, Receiver was TT3200 pci card.

Rob

G4WIM
Posts: 109
Joined: Thu Jan 29, 2015 8:36 pm
Location: Freckleton, Lancs

Re: 146.5MHz rx threshold ?

Post by G4WIM » Tue Aug 15, 2017 10:06 am

Hi Rob,

thanks for the reply - looks as though it's in the right ball park ready for 'air testing' - just hope there's not too many large out of band signals around which may cause blocking problems.

That said the input to the LNA (good old BF981) is tuned and it's followed by a 3 stage helical which gives a well defined bandwidth etc - as per another of my posts elsewhere on this forum.

I'll report back how it works out in practice.

73 Tim

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