[hpsdr] Alex

[Phil Harman]

Hi Frank, 

Elecraft use T50 cores in the K2 100w PA without any problems. In terms of the DDS we are using 18 bits for the sine/cosine calculations and a high quality 14 bit DAC.  

On receiver the DDS  (actually a CORDIC NCO) spurs are >100dB down and whilst on transmit the DAC will degrade this somewhat even with  just a 55MHz LPF on the output of the DAC we are well within the FCC requirements for a transmitter.

I don't think there is any cause for concern. In fact given that there are no analog mixers involved, and we are generating the RF output directly at the input to the DAC,  Penelope could well turn out to be one of the cleanest transmitters around. 

73's Phil...VK6APH 


  ----- Original Message ----- 
  From: FRANCIS CARCIA 
  To: hpsdr at lists.hpsdr.org 
  Sent: Friday, July 27, 2007 12:18 AM
  Subject: [hpsdr] Alex


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  I would avoid using T50 cores at 100 watts. Might get away with stacking 2 or 3 cores.
  Red for low end and yellow 40 meters and above
  T68 work well up to around 200W. Also allows larger wire to keep the resistance low.
  Check RF current rating of caps might need to parallel multiple units to keep them cool.
  Stay away from XR7 dielectric caps. 
  Relays use the ones about the size as a SRA1 mixer can. Then can take the voltage. 
  Add at least a gas tube for static protection. I would think some sort of a clipper needs to be ahead of an expensive A/D. Biased Transorbs isolated by low C fast diodes at least.
  I'm a bit worried about a D/A making a clean signal. We know what a D/A in a DDS does, how is this different? frank wa1gfz


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