[hpsdr] MDS

[Chris Bartram]

In the 1980s I had a 2m to HF transverter - yes 2m in, all HF amateur bands 
out! - in production. Although I say it myself, it worked very well. The 
limitation was largely the limited dynamic performance of the then current 
VHF transceivers.

One of the reasons for the good performance was that I used a frequency 
variable attenuator ahead of the SL6440C receive mixer to compensate for the 
increase in antenna noise at the LF end of the spectrum. From memory, I 
derived the required receiver sensitivity from data in 'Reference Data for 
Radio Engineers', setting the noise figure to about 30dB on 1.8MHz and 
tapering to about 10dB at 30MHz. These figures, in practice, seemed more than 
adequate, even with electrically small antennas.

My inspiration for this came from Racal, who, I think, at one time had a 
frequency dependent attenuator in their catalogue.

Vy 73

Chris
GW4DGU 

 1155394354.0