[hpsdr] IP3 >+50 dBm ?

[k3bu at optonline.net]

----- Original Message -----
From: KA2WEU at aol.com
Date: Monday, August 27, 2007 8:35 am
  
Good Morning,
 
There are 2 issues:
 
>>If the synthesizer is too noisy, a interfering signal , based on the reciprocal mixing effect, will mask the wanted signal. This is the same effect as if a amplifier of mixer generates discrete birdies, but here it is broad band noise. Both will prevent you from copying the wanted signal.
 <<
 
I think it is remarkable that we have mixer making such demands on the synthesizer noise. Dismissing it because phase noise in oscillators, I think it should be now incentive to push the envelope in the oscillator design, filtering etc. in order to take advantage of the mixer.
 
>>Likewise you can not build a transmitter with sufficient low distortion or noise to match this. There are NO IP3 > 50 dBm transmitter. In a band with many stations the noise floor will be so high from transmitter contribution and atmospheric noise  the such an ideal receiver would have no advantage unless  the synthesizer and ALL transmitter would be cleaned up.   
Nobody here seems to work on these 2 issues  TOGETHER
73 de Ulrich
 <<
 
True with loud signals, but when we are dealing with weak signals in the noise, the noise generated by transmitter is way below and not in the picture. Atmospheric noise can be dealt with directional and steerable antennas. 
On low bands  160/80 m when dealing with weak signals and directional receiving antennas next to killer local signals, every dB of IP3 and weak signal handling with next door strong signals is very much desirable.
 
So, I would like to see the next step in super clean oscillator design, complementing the H mixer. Thanks for all the work, exciting times in radio are here again!
 
Yuri, K3BU
 
 
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