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Amplifier selection | Amp and Preamp

In SPECTRAN V6 control ribbon, which is the expected usage of Amp selector:
I have a SPECTRAN V6 with internal amplifier
I also have en externa UBBV2 preamplifier.
Does selecting pre-Amp automatically connect internal preamplifier ?
Does selecting Amp automatically compensate External preamplifier ? isn't that already done in calibration ?
Which is the exact usage?

The Spectran V6 has up to two internal amplifiers, the one called „Amp” in the RTSA-Suite software is always available, the one called „Preamp” requires the purchase of the Spectran V6 Preamplifier option.
Any external amplifiers must be specified using the “Calibration” block.

 

The noise floor of V6 remains unchanged when the PRE is on and off.

Please compare the reference level settings while changing the amplifier status!
Turning on an AMP stage allows lower reference level settings, which significantly increases the SNR.

Uploaded files:
  • amp_vs_reference-level.png
  • amp_vs_reference-level2.png

20dB gain is not observed when looking at the noise level. We bought pre-amp option but this does not seem to work. In the best case a 10 dB is observed when amp disabled  / amp enabled.

The PREAMP is an additional amplifier and improving the noise floor not the signal strength so i think you are mixing things up.

If you activate BOTH amplifier stages the max you can reach is around -170 dBm/Hz DANL that's simple physics and a great value!

You can check the amplifiers by adding a 50 Ohm load to the Rx.

Use the default mission (at 2450 MHz)

With amplifier ON and RefLevel set to -38 dBm (max) you should see a -110 dBm AVG noise floor.

By activating "both" (Amp and Preamp) and the RefLevel set to -60 dBm (max) you should see a -115 dBm AVG noise floor.

The preamplifier improves the noise floor by 5 dB.

Tuning to 5800 MHz will improve the noise floor by 10 dB instead.

The higher the frequency the bigger the NF improvement with the preamplifier.

Thank you for your informative reply:

1. Since the preamp gain is 20dB , how come I only see +10dB difference in the noise floor @4GHz ?    From the schematics, I see that the gain of amplifier is +17dB. Shouldn't this change the noise floor to additional 17.5dB when both amp and pre-amp are used?

2. The noise improvement is only for the low sampling. if I increase the average sampling to 1E6 (max.) I don't see any improvement at noise level. Any explanation for this?

Thanks, A.

As mentioned you can NOT go below the physical noise floor of the unit even if you add 100 amplifiers.

Since the SPECTRAN V6 offers a superb NF of 4 dB you can not go below -170dBm/Hz DANL. As a result your unit is working perfect 🙂

Please check out the wiki at https://en.wikipedia.org/wiki/Minimum_detectable_signal for more details.

 

I used an external amp with a gain around 40dB and the average noise level has changed 40dB as expected. Why I don't see the same effect when I enable/disable amp and preamp in SpectranV6? I still did not get the answer that how much gain the amp an preamp will add to the RF chain and why the pre-amp have no effect on the noise level . I also used a small signal to see the difference but no improvement on SNR.

Uploaded files:
  • Screenshot-31.png
  • Screenshot-33.png

The internal amplifier offers around 17 dB, the optional pre-amplifier around 20 dB of gain but as mentioned you can not go below the physical limit of -170dBm/Hz DANL with 4dB system NF so a regular external amplifier can´t improve those specs.

The only way to get higher sensitivity would be to use an external super low noise amplifier with a NF below 0,5dB. In this case you might be able to optimise the performance by another 1-1,5dB to reach around -171,5dBm/Hz DANL.

Your screenshots for sure did not include the calibration for the gain and the NF of the external amplifier so those measurements are wrong.