EME 2016 Venice, August 2016 1 Failure levels in LNAs Update on - - PowerPoint PPT Presentation

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EME 2016 Venice, August 2016 1 Failure levels in LNAs Update on - - PowerPoint PPT Presentation

Feb 10, 2023 454 likes •729 views

Sam Jewell, G4DDK EME 2016 Venice, August 2016 1 Failure levels in LNAs Update on the VLNA Investigation of the failures seen in the VLNA Nature of the failures Method of the investigation Results Conclusions

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Sam Jewell, G4DDK EME 2016 Venice, August 2016

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Failure levels in LNAs

  • Update on the VLNA
  • Investigation of the failures seen in the VLNA

– Nature of the failures – Method of the investigation – Results – Conclusions

  • Over-coax power feeding

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VLNA Update

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0,05 0,1 0,15 0,2 0,25 0,3 0,35 0,4 0,45 500 1000 1500 2000 2500 3000 3500 4000 Noise figure (dB) Frequency (MHz)

Typical VLNA noise figure

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VLNA typical gain

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5 10 15 20 25 30 35 40 432 1296 2320 3400 Gain (dB) Frequency (MHz)

Typical gain

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Bias conditions for 23cm

  • TR1

– Vds = 1.5-1.8 volts – Id = 14.8 – 16mA

  • TR2

– Vds = 2.94 volts – Id = 66mA

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~1.6V 2.94V 66mA 15mA

Typical bias conditions

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7 2.7pF 8.2pF 13nH 2.7nH LNA input Active device

Input noise matching circuit for the VLNA23

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Nature of the failures

I wanted to investigate two areas in particular

  • 1. Gain/noise figure anomaly
  • 2. Is it better to keep power on during transmit?

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Gain/noise figure anomaly

  • Reports that gain appears normal.
  • Noise figure has increased

Manifestation

  • Preamps appeared to be working normally but signal reports

were ‘asymmetric’. Receiving better reports that able to give previously.

  • Observed in several different preamps, not just the VLNA

– ATF53189 PHEMT has been shown to exhibit the same effect at 2m

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Power on or off?

To test claims that the preamp can ‘survive’ higher levels of input signal if the power is left

  • n during transmit

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Failure tests

Testing for the gain/noise figure anomaly and power on/off survival can be tested as a single set of measurements

Power on Increase the power into the preamp in steps, soak for a set amount of time, measure noise figure, gain and input return loss at each step. Repeat until preamp fails. Note level at which failure occurs and any changes. Change FETs Power off Repeat above tests until failure. Note level at which failure occurs and any changes.

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No one wants to deliberately blow up their favourite preamps, do they?

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Failure tests

  • ‘Soak period’ varied from 3 minutes to 1 hour

at each of the input levels

  • Noise figure, insertion gain and input return

loss measured after each period

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0,1 1 10 100 5 10 15 20 Noise figure and gain (dB) Input level (dBm)

Early results - Power on Table 1,2,3,&4

Noise figure increase Noise figure fail

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0,1 1 10 100 5 10 15 20 Noise figure and gain (dB) Input level (dBm)

Early results - power off Table 4*,5 and 6

*Two table 4! Noise figure increase Noise figure fail

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Later test results with isolator

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0,1 1 10 100 5 10 15 20 Noise figure & gain (dB) Input power (dBm)

Latest results - Power ON

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0,1 1 10 100 5 10 15 20 Noise figure & gain (dB) Input power (dBm)

Latest results - Power OFF

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Conclusions 1

  • The noise figure/gain anomaly has been
  • bserved in testing and usually occurs in a

limited input range before complete failure

  • Does not happen every time.
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Conclusions 2

  • Occurs mainly between +12dBm and +17dBm input

– Anomaly due to gate puncturing?

  • It seems to be due to the onset of gate current

– Too low to be measured ( maybe picoamps?) – At this level of gate current the gain is largely unaffected

  • Most devices fail completely between +20dBm and

+23dBm input

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Conclusions 3

  • Doesn’t seem to be due to RF heating, directly
  • It has been observed in both HEMT and

PHEMT devices

  • Second stage (ATF54143 PHEMT) unaffected

as first stage limits input signal level

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Conclusions 4

  • Keeping power on during transmit does not

confer any advantages – see next slide

  • VLNA23 is able to withstand a larger input

signal than previously recommended

– If I can afford the FETs I will check the other bands!

  • Failure suspicion falls on relay isolation

– Need for dynamic rather than static testing - Spikes

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Power feed over coax

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120R = 10V @85mA Preamp and isolation relay Powered in parallel Option to use 20-24V

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Thank you

More details will appear on my web page G4DDK.COM Blog: G4DDK.BLOGSPOT.COM Twitter: DXING

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Basic HEMT structure

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