Thursday, December 1, 2011

10 GHz Receive Pre-amplifier Considerations

The last potential upgrade on your list would probably be a receive pre-amplifier. Unless you have an unusual situation, you'll probably not see much benefit. Unusual situations include:
  1. Lossy transmission line between your antenna and 10 GHz transverter.
  2. 10 GHz transceiver with a poor noise figure (that can't be fixed).
  3. EME operation with low background noise where every fraction of a dB counts.
KC0IYT - Glen has pointed out that you may be able to test your current receive sensitivity by just pointing your antenna towards a noise source (houses, people, trees, etc.) and monitoring for an increased noise level compared to the open sky background noise. Compare noise figure specifications between different transverters and receive pre-amplifiers to determine if the potential improvement is worth the expense and additional complexity.
Commercial receive pre-amplifier sources:  
Kuhne MKU LNA 101AS

Costs range from around $100 (kit) up to $250.

Surplus receive pre-amplifier Source - Modified KU band LNA's

  • K0AWU - Bill uses a surplus KuBand LNA to provide about a 1db NF and 20db gain to overcome superflex cable loss on the receive path from his tower to shack.

        Potential Benefits of Receive Pre-amplifiers:
        1. Overcome receive path losses from transmission lines, adapters, relays, connectors, etc.
        2. Optimize the transmit path without concern for the receive path, if a choice is necessary.
        3. Improve your station's noise figure to compensate for a poor or remote transverter.
         The Care and Feeding of Receive Pre-amplifiers:
        1.  Must be connected directly to a low-loss antenna relay for maximum benefit.
        2. The potential for severe overload from other stations nearby and/or on adjacent frequencies dictate that you reduce the gain in the receive path down stream of the receive pre-amplifier. A lower gain receive pre-amplifer (single stage, >12 dB) may be better than a higher gain unit (dual stage, >22 dB), depending on your station configuration.
        3. Pre-amplifiers must be well protected from any RF power using relays with high isolation.
        4. Proper sequencing becomes more important to insure that protection relay(s) have completed switching before any RF power is applied.
        5. Never allow your antenna relay to be switched during a transmission!
        6. Filtered DC voltage is necessary to avoid injecting power supply noise.
        7. Unterminated receive pre-amplifiers can go into self oscillation.
        8. Pre-amplifiers are subject to potentially destructive RF transients from adjacent bands.
        9. Gain and can deteriorate over time so be sure to measure it while still in new condition.
        10. Rain, humidity and vibration can degrade your pre-amplifier electronics and/or connectors performance, over time.
        Receive Pre-amplifier Configurations:
        >>>under construction<<<

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