Wideband amp wanted for a noise generator to feed my SA

[Chris Wilson]

I want to use the noise generator I have to tune a band pass filter on my SA. What will it need amplifying to be usable?  Has anyone a link to a simple to make amp to get the signal from around 100kHz to about 1Mhz up to a suitable level please? Also what does ENR mean in the spec sheet attached please, and what output is this thing supposed to have on its own? SA is HP8568B Thanks

[rfeecs]

I would think you could get flat gain to 1MHz with a decent op amp.  For higher frequencies there are MMIC gain blocks, but they might not have very flat gain.

ENR is Excess Noise Ratio.  It is approximately the difference in noise power in dB between the noise source powered on and off.  This gives the exact definition in section 3:
http://literature.cdn.keysight.com/litweb/pdf/5952-8255E.pdf

Turned off, it would have an output noise power at room temperature of about -174dBm/Hz.  So if ENR is 25dB, then turned on the output noise power would be approximately -174dBm/Hz + 25dB = -149dBm/Hz.

[jpb]

It is a long time since I worked with MMICs but if you're looking for wide-band gain then Distributed or Travelling Wave amplifiers will give this - back in the 80s we had chips that went from DC to 18GHz.

I don't know if they are commercial products though.

A random search came up with this:

https://datasheets.globalspec.com/ds/2844/AvagoTechnologies/15282232-A3AA-486E-827E-78BE3BC49BA2

[technogeeky]

I'm curious - why would a regular old LNA not work for this application? What goes wrong when you try to amplify a noise source with a LNA? There are tons of LNAs with gains of up to 40dB out there for not very much money.

[Chris Wilson]

Thanks for the replies, let's get specific though, would this do the job please?

https://www.ebay.co.uk/itm/122562329344

[rfeecs]

Thanks for the replies, let's get specific though, would this do the job please?

https://www.ebay.co.uk/itm/122562329344

According to the datasheet, your HP8568B has a noise floor of about -130dBm/Hz at 100 kHz and -150dBm/Hz above 1MHz.

This amplifier will add about 35dB of noise, so that brings the noise source + amplifier up to about -149dBm/Hz + 35dB = -114dBm/Hz.

So you will have about 16dB of dynamic range at 100kHz to 36dB of dynamic range at 1MHz and above.

So you should be able to see something with this amplifier, but you may want more gain if you need more dynamic range.

[Chris Wilson]

Thanks again. As a lowly intermediate licence holder I now have to ask, will mi likely need more dynamic range to tune a filter to block mainly uk high power broadcast band interference from the LF ham band which is 136 to 138khz? The main big power UK station is BBC Radio 4 on 198khz. Thanks

[rfeecs]

I'm not a ham, but I guess if you can see your wanted signal and the unwanted signal on the spectrum analyzer, the difference in level between the two should give you an idea of how much suppression you need.

[chris_leyson]

A simple PRBS generator , pseudo random binary sequence generator, would do the job, just clock some simple shift register logic at 50MHz or so and low pass filter the output, job done.

[Wolfgang]

Hi Chris,

I think the amp used here is an INA02186.

I have built a lot of preamps with this one and they work perfectly. And 32dB gain at the low end is quite good.

https://electronicprojectsforfun.wordpress.com/rf-module-gallery/the-amplifier-module-gallery/mmic-amplifiers/an-ina02186-mmic-amplifier/

[Wolfgang]

I agree, but its not so easy to achieve a wide flat frequency range.
I built some, if interested look here:

https://electronicprojectsforfun.wordpress.com/making-noise/digital-noise-sources-i-have-built/

[Chris Wilson]

Thanks for the further replies, I am using 2 of these in series to up the signal from the commercial noise source and my SA (HP8568B) is now working well to see my band pass filter efforts. I am also (possibly naively) using one as a pre amp for my Red Pitaya LF 137kHz low frequency ham band receiver. It seems to work well and I use a low noise adjustable voltage source to set the gain as needed. Some good info thank you everyone for the replies

EDIT: Two of what, put the damned link in Chris, you dozy pratt

https://www.ebay.co.uk/itm/0-1-2000MHz-RF-wideband-amplifier-gain-30dB-low-noise-amplifier-LNA-TK/263840684787?hash=item3d6e215af3:g:l98AAOSwZ4dZNQOF

Apologies, getting old....