Sunday, December 13, 2015

2x LNA4ALL for the Hydrogen line measurements

The LNA4ALL is a wide band LNA that cover also the Hydrogen line, 1420 MHz frequency. I receive a lot of e-mails from the guys asking for the performance of the LNA4ALL at the 1420 MHz with idea to use two LNA4ALL in series configuration to achieve the higher overall gain. The H-line guys main concern was Noise Figure and then the Gain. The feedback from the H-guys was evaluated  where we found the mixed experience. Some of them were happy with the setup, some of them admit that the LNA4ALL is good for the second stage LNA only and we have guys without instant success and the proper results due to various technically related problems deserving the completely separate new post. I will try to explain what is the value you get  for the money invested.

I already mention that the LNA4ALL is a wide band amplifier. Designing the amplifier the main goal was to end up with the unconditional stability where we count that the users may forget to connect the input/output, may short the input or output or may have all kind of mismatch situation. The LNA4ALL should handle all this situation and not run into oscillations nor fail to operate or damage the attached equipment.
The second goal was to get the low Noise Figure and the maximum possible Gain that the active device can deliver on such a wide range of frequencies. At the same time we aim to the high IP3 numbers where the LNA4ALL will not run easily into non-linearity and make more damage to the receiver chain than not running the LNA at all. The LNA current consumption was evaluated and this became also one of the limiting factors.

The simple question was, can LNA4ALL compete against the LNAs designed only to operate on 1420Mhz ? The even simpler answer is NO, it can not. The main difference is that such designed LNA should have a lower NF (0.2-0.4 dB), stability around 1420 MHz (at least), and a higher Gain (35-40 dB). Most of the LNAs that are targeting the H-line operation are within the mentioned specifications. The only drawback may be the price. They are made as plug&play units and the user does not have nothing to "tune" and play around the hardware. If they are damaged, the user must be highly skilled to repair it and tune it for the best performance.

Comparing to the above mentioned LNAs the LNA4ALL will deliver slightly weaker performance and it is on you to decide whether it will suit your needs or not. Some of our H-line users have the access to a really nice, and the most important, calibrated measuring equipment. I will share with you their measurements so you can evaluate the LNA4ALL for the H-line operation. The setup used was the two LNA4ALL connected in series with the side pads separated power supply. The first measurement was the S2,1 (Gain) measurement performed on the network analyzer. Gain of 2x LNA4ALL @ 1420 Mhz was 31.35 dB. Of course, using the only one LNA4ALL the gain will be half of that.

The second measurement was performed using the Noise figure meter and the 14dB ENR noise source head. Noise figure measured @ 1420 Mhz for the 2x LNA4ALL in series configuration was 0.698 dB and the gain of 31.9 dB. The peak in the NF graph around 1.7GHz was due to the power supply used. In the later measurements with the other power supply used the peak was gone.

The 14dB ENR noise head used in the second measurement is "universal" noise source where the  low noise, and the high noise devices can be measured. This head suits perfectly for the mixer noise figure measurements. I ask the guys if they have the possibility to repeat the same test but with the lower ENR noise source to get more accurate (higher NF) results. They reply with the following graph. The noise figure of the 2x LNA4ALL in series was 0.757 dB and the gain of 32.2 dB @ 1420 MHz. You can note that the peak around 1.7 Ghz at the NF graph was gone.

All measurements were performed using the 2x LNA4ALL without milled housings, just the bare boards with the SMA connectors attached.


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