Chinese R.F preamplifiers and their performance


Well there are several types for sale on the web , so I bought a sample of each and played with them on the RF bench for use as RF preamps for ham radio applications

 

   They all make the usual outrageous claims but I suspect some attributes of them may be useful in different situations , I have  measured gain, input and output SWR using and E5061 300Khz to 3 GHz VNA and Noise Figure with an HP8970B with the internal 2045 Mhz option and N8972A Noise figure meter with 1500 Mhz Limit . I have gathered several noise sources, a Noise com NC346 ~15 dB ENR which has had an additional calibration at some time in the past (new sticker over the original) a cheapy chinese sold in USA ? Off the internet calibrated from 10 to  1800 Mhz ~`15 dB ENR and a “6” dB ENR RF2035 from G8FEK.com, calibrated from 10 Mhz to 3.3GHz also from the internet,  but made in England and that comes with a calibration certificate as well, a much better manufacture and a website to back its pedigree . If you cant afford a .1 to 18 GHz real one go for the RF2035 noise source they just seem so much better all round .

Noise figure measurement is fraught with pitfalls

Firstly the accuracy is mostly dependant on the accurate calibration of the Noise Source . A good commercial noise source is quite expensive.. New US$2000 plus , but you can get good second hand ones on the market . Most expensive noise sources hold their calibration for a long time although it is recommended they are recalibrated yearly $$ . The Usual branded ones by HP.. Agilent.. Noisecom and Eaton et el .. are usually calibrated to two decimal places after the decimal point . eg 15.25 dB ENR and its not a cheap process to achieve this against a special accurate ENR standards.

The cheaper models are usually calibrated only to one place after the decimal place eg 15.2 dB ENR …. Accuracy is reflected in the price..

Noise figure meters calculate the gain and noise figure of DUT,s using the difference between the thermal noise level generated by 50 Ohms resistance at e.g. room temperature and the artificial hot noise source of a calibrated noise generating semiconductor diode . Some sources are 15 dB ENR for moderate to high  noise figure preamps and some are 5-6 dB ENR used for low to very low noise rf preamps.

Because of the comparison of noise levels , you must set the actual ambient room temperature in Kelvin, into the instrument before calibration ,so it can calculate the room temperature noise level and also load in the correct ENR level in dB (s) at the frequency (ies) of interest from the calibrated source , get either of these wrong and the gain and noise figure measurements will be incorrect..

The other factors are the matching of the DUT to the noise meter , ideally a 50 ohms conjugate match with low VSWR for accurate power transfer .

When performing NF measurements , I find external RF pick up can cause a big headache. The NFA is a very sensitive wide band ( typically 4 Mhz) receiver and the testing of a low noise high gain rf preamp, if not shielded very well , will pick up external RF and add signal to the calibrated noise already going through the system and change the  detected levels at the rf noise detector . This interference is seen as a bump on the noise figure curve..

Some preamps have to have extra shielding in place at the input to minimise this potential RF pickup problem . see photo below .
I have just been fortunate to purchase a respectably priced next model HP Noise figure Analyser an HP N8972A which covers 10 Mhz to 1.5 GHz and to 0.1 dB resolution , I would have dearly loved a N8973A which does 10 to 3 GHz and has slightly better performance down to 0.05dB resolution , but these are still commanding good prices on the second hand market , and I don’t have a recently calibrated accurate  commercial noise source , so it is still a pipe dream.

However the overall procedure of measuring true Noise figure is dependant on having an accurately calibrated broadband noise source ie accurately known ENR at various frequencies of interest ..There are other influences that come into place, losses in connectors ,mismatch losses, temperature of the system, ie  accurately known so called cold temperature . there is so much literature written on the subject .look on the web !!

The HP8970b will still hold its own next to a 8972 for performance , the advantage of the 8972 is a floppy drive / ram drive for storage and retrieval of data and LCD colour display for display gain and noise figure.  

Im still learning about taking noise figure mesurements  so take my derived information with caution ....

I did  play around with changing the supply voltage of preamps to  see what it did to noise figure  ..Changes may be due to the active device changing input impedance  hence apparent  noise figure  changes  ??? 


 

This is the screening using copper foil over the rf input see top preamp 

 to keep  external RF out otherwise it interferes with the NF meter operation 


No. 1             40 dB gain and 0.001 to 3.0 GHz


gain verses frequency response 300 KHz to 3 .0 GHz along with noise figures


10 MHz 36.04 db gain NF of 4.47 @ 12.27 volts

10 MHz 32.45 NF 4.12 dB @ 8.0v

50 Mhz 35.64 dB @ NF 4.09 dB 8.23 v

50 Mhz 39.03 dB @ NF 4.59 dB 12.00 v

925 MHz 34.52 dB gain NF 4.97 @ 12.77 v

925 Mhz 31.09 dB and NF 1.44 @ 7.92.0 v





 

No. 2   5-6000 Mhz preamp

This amp is based on the RFMD active device SBB5089Z . It is .internally matched to 50 ohms, 5v operation and typically 75 mA. Gain is quite flat with a gentle downward slope to 6 GHz from 20.5dB to 15.5 at 6 GHz noise figure is 3.9-4.9 dB at 1950 MHz max output is 19.5 dBm at 50MHz-2GHz

 


swept response 300Khz to 3 GHz ripple probably caused by coax leads !??

Response from 300 Khz to ~100MHz gain only dropped 0.5 dB !!





N8972A dual mode display

 The measured  gain of the amp on the VNA  and the NF meter  are different  this could be due to the calibration of the noise source  i used  ,  to tight to purchase a brand new calibrated Agilent one 

 

No.3  Avago mimic INA02184 identified by NO2 on top of mmic .. Data sheet .. 50 ohm in and out with a typical power gain of 31 dB…0 to 500 MHz noise figure of 2.0 db achieved at 35 mA (absolute max 50 mA) 3.5 dB at 2 GHz ,This module is configured for 12 V operation The 3db bandwidth is 0.8 GHz but it is essentially flat from 300Khz to 500 MHz and over ,max rf out is +10 dBm


12v DC (or more correctly 38 mA) is best noise figure


Particularly Flat frequency response 32+/- 0.5 dB to well over 500 MHz

.


Avago input VSWR on the VNA

Avago output VSWR


gain/ NF on N8972A note bump in noise figure.. that’s due to external RF pickup !! 

hence the need for good rf free  environment 

 

 

 N0. 4     5 - 3500 MHz 



Unknown active device  I will have to crack it open !! 

VNA gain sweep .003 to 3 GHz

 


  No.5  NDWZ preamp

Active device is a SPF5189Z 90 mA @5 v 26 db gain at 54 Mhz nominal 50 ohm input and output impedance .


    


10 MHz 9.73 db gain NF of 3.86 @ 5.04 volts

30 MHz 24.53 dB NF of 1.35 @ 5.0 v

30 Mhz 23.89 dB NF 1.09 @ 2.98v

 50 MHz 25.12dB NF 0.92 dB @ 2.26 v

50 MHz 26.35 dB NF 1.03 dB @ 5.0 v

150 MHz 26.19 dB gain NF 0.56 @ 5.0 v

150 MHz 24.9 dB NF 0.47 @2.26 V

430 Mhz 22.26 dB and NF 1.08 @ 3.34.0 v

430 MHz 22.65 NF 1.12@ 5.00 V



NO.6   SPF5189

The SPF5189Z is a high performance pHEMT MMIC

LNA Ultra-Low Noise Figure=0.60dB @900 mhz 18 db gain, 5v and 90 mA

10 MHz 24.48 db gain NF of 5.06 @ 5.04 volts

30 MHz 26.16 dB NF of 1.63 @ 5.0 v

30 Mhz 24.55 dB NF 1.07 @ 1.98v

50 MHz 25.15dB NF 0.95 dB @ 2.76 v

50 MHz 25.92 dB NF 1.14 dB @ 5.0 v


140 MHz 25.31 dB gain NF 0.59 @ 5.0 v

140 MHz 24.22 dB NF 0.51 @2.36 V

430 Mhz 21.19 dB and NF .92 @ 2.39.0 v

430 MHz 21.99 NF .92 @ 5.00 V

 



.SPF5189 device gain and noise figure


No.7   TB 386 operates on 3-5 v



Unknown Active device

 

10 MHz no good at 10 Mhz

30 MHz 13.95 dB NF of 3.35 @ 5.0 v

30 Mhz 10.4 dB NF 2.46 @ 1.97v

50 MHz 19.15dB NF 1.95 dB @ 5.00 v

50 MHz 17.00 dB NF 1.81 dB @ 1.98 v

 

146 MHz 22.26 dB gain NF 1.09 @ 5.0 v

146 MHz 20.90 dB NF 0.51 @2.53 V


430 Mhz 20.01 dB and NF 2.08 @ 3.2.0 v

430 MHz 20.56 NF 1.98 @ 5.00 V


There  are some  more I have to document    soon as I have data I will add it to here 

 

73's  Mike  ZL1BTB

 

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