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Old 18th Oct 2018, 11:23 pm   #15
G0HZU_JMR
Dekatron
 
Join Date: Sep 2010
Location: Cheltenham, Gloucestershire, UK.
Posts: 3,077
Default Re: MuTek Pre-amps for the FT290R

To show why a typical setup using the TR9130 was classed as deaf I put together a quick spreadsheet for antenna temperature, feeder loss and receiver noise temperature (converted from noise figure in dB).

I compared a TR9130 fed via coax with 1.5dB loss to a typical 'serious' setup using a masthead preamp with an overall receiver noise figure of 1.2dB.

I compared the difference using a slightly elevated beam that was pointing in a direction with low galactic noise. I really can't remember how quiet the 2m band noise can be when this is done but I chose an antenna noise temperature of 250K.

So when both are fed with the same antenna there is a difference in S/N ratio of about 7dB. This is because the TR9130 has an 8.5dB noise figure and this is made worse by a typical (longish) feeder loss of 1.5dB. However, if the antenna noise temperature shot up to a not unreasonable 2000K the difference between the TR9130 and the 'serious' setup falls to about 3dB.

So the decision to adopt a low noise preamp depends on what you want to do with the radio and also on how noisy the band is. To really appreciate the difference in 2018 you would probably have to be beaming your antenna in a quiet direction. Maybe someone with experience of the 2m band today can comment because I really don't know how low the rural/urban band noise can go on 144MHz in 2018 when a beam is rotated around at various times of the day/month.
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Regards, Jeremy G0HZU

Last edited by G0HZU_JMR; 18th Oct 2018 at 11:29 pm.
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