TWS-N15 Noise Source: checking out some design alternatives

So far, we have mainly been discussing series type noise sources, i.e., noise sources where neither anode nor cathode are connected to ground. Another common design is shown here – the shunt configuration (one port of the noise generation element grounded).

noise source bfr93a shunt

The assembly, more or less just a little blob of solder with a few tiny parts inside… mostly, 0603 SMD format. The output attenuator (not shown) is a 14.5 dB(!), 18 GHz coaxial attenuator.

noise source bfr93a shunt assy

Some quick measurements, at bias currents of 2.5, 5 and 7 mA…. still, there seems to be a lot of 1/f noise (increase of noise power at lower frequencies). This is model #1, with a 22 nF capacitor (see schematic)

noise bfr93a shunt configuration 1

Don’t really see any advantage over the series variant of the noise source. But will test further.

…Progress on another front, ordered a set of PCBs – they can be used for various noise source configurations. Not yet a “prototype”, but need to see what kind of GHz performance is available from such design, and how reproducible it is. No current source yet on this PCB – will add later, or on a separate board – to limit shielding to the RF section.

noise source pcb 150827-2

11 thoughts on “TWS-N15 Noise Source: checking out some design alternatives”

    1. Very interesting! Will check it out. Also experimented with some Russian noise diodes here with good success.

          1. Yeah, right. But dont overdo it with the light, or it will turn into a roman candle and burn out after a very short time 🙂

            It could also be that a red hot anode could also emit some electrons, maybe altering noise output. I need to check.

  1. Hey, this looks very interesting. I am looking for a noise source for 5GHz-6GHz. Do you think that this will work?

    1. Probably yes, but it won’t have 15 ENR noise power unless you adjust the attenuator. In any case, I would suggest a design using a coaxial attenuator rather than the discrete SMD resistor type at these frequencies to get reasonable return loss. I had good results in the past by soldering an noise transistor directly to a good quality SMD connector, and using a fixed attenuator. The current source will stay the same. Good transistors are BFR93A or similar. Drive currents about 8-12 mA.

      1. Thank you very much for your response. I am pretty new in RF so I have a lot of reading up to do. By “SMA connector” you mean something like an U.FL connector?

        I was thinking about using an SMA connector, since this is what I use throughout the System.

        And you just solder the transistor to the connector? No other components? This is probably a stupid question but at the moment a lot of the RF schematics look a bit like magic to me. I guess I should simply start experimenting.

        Thanks for the hint with the coaxial attenuator. I guess I will order some BFR93A transistors and start experimenting.

        Again, thank you for your Time.

          1. Ah alright, just wanted to double check I did not miss-understand.

            You have been very helpful – thank you again.

            Grüsse aus AT.

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