I just finished a 3 pole 20m band pass filter. Looks good on the NanoVNA. I used an odd mix of surface mount capacitors, hand wound Amidon toroids, and 1970s Soviet surplus trimmers. Very happy with the result though! #HamRadio #AmateurRadio
@relistan I did this at the 100W power level for colocated stations in the ARRL FD contest. I found that the key to getting high Q from the toroidal inductors, was to use magnet wire at least AWG #14 for the higher bands, so the losses would be well under 1dB.
I used an LC coupled-resonator topology to get low component value spread, and transformed the internal impedance to 300 ohms to get reasonable inductor values. Capacitors were 1-2kV mica, and tuning was done by adjusting the turn spacing on the toroids.
@azstefano well you鈥檙e a lot more advanced than me, clearly. I am happy with what I did on my first try.
@relistan It was my career. Also the capability was built into an old Windows design program called Elsie. Experience does help you to get the most out of such a tool.
What you did was excellent - a nice physical layout too. And BPFs can be useful with many of the SDRs that expose their ADC close to the antenna port without much filtering.
@azstefano thanks. Well I have a lot to learn but I鈥檓 trying! I built a 40m direct conversion receiver which works great. Because I prefer 20m I thought I鈥檇 try my hand at a 20m version with lots of improvements. After that maybe a BITX20. Both would need a bands pass filter so I started with a 3 pole because that鈥檚 what the BITX20 uses. But I didn鈥檛 like the design of that one so I made one that works better with what I have. Maybe thicker wire and bigger toroids would be better like you did.
@relistan I think BITX is a sound design: Ashhar Farhan is good friends with some older engineers from Tektronix and they have mutual respect for each other. He has a good blog and I believe he's working on code + DSP for a ARM Cortex type board which will make for a more capable RX. In fact here it is, the sBITX: https://www.vu2ese.com/
BTW, your blog leaves me in the dust on code - I've dome very little of that and it's usually been derivative.
@azstefano thank you. Code and systems stuff I鈥檝e spent 30 years at professionally. But electronics only here and there for 15 years when I had some hours on a weekend. Radio electronics are new to me in the last could have years only. Sorry I was defensive when you first responded. Yeah Farhan has done a bunch of cool stuff. I was looking at the original BITx20 because it鈥檚 simple and I can understand it. But I might use a digital VFO anyway. Or the one from his Daylight rig. We will see!
Another shot further down the band
