If Brackets (or Analog VFO's) is not your thing, then today something for a weekend project. Another Swiss Army Knife is the 2N3904 NPN transistor. This device shows up everywhere and anywhere literally covering the audio to RF Spectrum. We are not going to showcase that device today!
Instead, we will be sharing something about its twin complementary PNP brother the 2N3906, which also can also function from audio to RF. Often the PNP devices are bypassed because the Emitter is the + side and the collector is the ground side. It is tough enough to keep the NPN devices on the straight and narrow now you are switching pins.
The two devices (2N3904 and 2N3906) are almost equivalent in specifications as to the Ft and device dissipation. The tricky part is how to use both the devices in the same circuit.
I have often mentioned the Plessey Bilateral amplifier circuit. For the anal-retentive blog readers, it is described in EMRFD, so it is OK to talk about it. I find it noteworthy that many US homebrewer's look with skepticism at any circuit until you say what seems to be the magic decoder ring words "found in Bitx or EMRFD".
The genesis of today's circuit comes from my separating out the 2N3906 device from the Plessey circuit and putting it to work for me. By design I simulated the circuit first in LT Spice and then used it in one of my more popular articles, the MC1496 Direct Conversion Receiver in SPRAT 187. For this application it was the RF Amplifier stage following the Band Pass Filter.
Now this is just like using your Nano VNA where you don't calibrate the device and have no clue what you are really seeing. The plot above at first glance seems awful. But from high to low (DC to 50MHz) the gain goes from 14dB to 9dB. The 3dB point is 10 Meters where you have 11dB gain. So a 10dB gain amp at 30MHz is not too bad --- especially for a simple set up with 5 resistors, 4 capacitors and for a device bought in bulk costing 4 cents.
[Special note because if I don't say it, I will get emails... R6 is for simulation purposes and not used in the actual build. ]
3906
I also find it interesting that this DCR has seen a far greater interest in ham homebrewer's outside of the US. Oh, right missing the Bitx or EMRFD magic words. I have a track on this from the requests for the Arduino code to run the DCR. About 70% are from outside the US with the total set being about 200 requests.
The LT Spice simulation has the info, and you can see the plot. This is a handy amp to have for general purpose usage when testing out various circuits. The cost is low, no toriods to wind and no special parts required with the added bonus you can even use the W1REX MePads to build it.
This is a one and done circuit and takes but a short time to build. It will operate with any voltage between 6 and 12VDC.
73's
Pete N6QW