[hpsdr] New HPSDR card for VHF/UHF ?

[ct1izu]

A narrow band termination will severly impact output intercept in diode rings.  Image products etc must also be terminated. Normal pratice is a dixplexer or these days a high dymanic MMIC.

Shel CT1IZU
  ----- Original Message ----- 
  From: Anthony Taylor 
  To: hpsdr at openhpsdr.org 
  Sent: Friday, September 10, 2010 5:10 PM
  Subject: [hpsdr] New HPSDR card for VHF/UHF ?


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        Shel,

        The diode mixer is already looking at 50 ohms across the entire IF range as it's terminated into a suitable LPF, adding a BPF may have some merit, however, if you provide an additional MMIC after the mixer (12db-3dB for the BPF loss) you are looking at adding about 9dB this would cause the ADC to overload, trying to do gain optimisation at the second IF after this will not help.

        BTW the RLP-50+ loss across it's passband is less than 2dB, the LTC 6400-20 provides over 20dB of gain so you are looking at atleast 18dB of gain before the ADC.

        73s,

        Tony
       




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