I'm trying to build a Mini Whip active antenna that receives 10KHz to 20MHz. But I'm having trouble finding the right components especially the transistors.
It calls for a J310 and a 2N5109, which are both hard to find.
When designing an antenna circuit what exactly is it you need to look for in a transistor? High frequency response? How does one go about choosing a suitable replacement?
I've tried using www.alltransistors.com to find similar transistors, but I'm not too sure what to compare. Obviously: polarity, max power dissipation, max voltages, maybe transition frequency? maybe the noise figure?
Other people have substituted these for a MPF102 and 2N3904 or BF245C and 2N2219A
I've also found other people using these as replacement, but I'm having trouble sourcing these too: BF245A, BF245B, BF245C, BF246 A/B/C, MPF102
I guess that these transistors are all very similar but subtly different, the problem for somebody out of their depth like me is knowing if it matters or not, if I use the wrong one will I end up with a terrible antenna?
On a similar note what being an RF circuit do you think its necceasary to have tighter tolerances on the resistors too? I was thinking about choosing +/-1% resistors over +/- 5% resistors?
Scroll down the pdf for circuit diagram: http://myweb.tiscali.co.uk/wgtaylor/PA0RDT-Mini-Whip.pdf