Homebrew 80m/20m SSB Rig Part 2 - Crystal Filter

Ladder crystal filter using four 8MHz crystals. 9MHz would have been a better choice, but these were all I had on hand. I will look to initially use a 4.1-4.5MHz VFO for 80m. If this turns out to be problematic as 4.1MHz is quite close to the upper end of 80m, then I'll switch to high side VFO injection and use 11.5-11.9MHz.

Please note that I have elected to use a simplified method for the construction of this filter (right or wrong) and have not used specific filter design software. I tried that in the past with little success.
The -3dB bandwidth is approx. 1700Hz
Uses Excel to plot the passband response.
We'll see how this performs in the circuit and go from there.

[Kdbpy]

Still taking notes....good stuff Charlie!

[daviddavidson]

cant wait for the next one...great video...

[ruhnet]

Thanks so much for this great content! Very detailed and helpful video. 73s

[chibill_mc]

Also ppm error in the RTL-SDR.com dongles is low enough that its not a problem. Anyone using a cheaper dongle will have to set the PPM error correctly first.

[russoft]

still waiting for crystals to arrive. Are you picking up that oscillation "as is" with the rtl sdr dongle or did you modify it for direct sampling below 24 MHz or whatever the lower cut off frequency is.

[aeai]

I was rewatching this video as I'd like to start working on my crystal filter. Have you considered using a noise generator and SDR dongle to plot the frequency response instead of doing in with your scope and excel? Maybe the accuracy isn't good enough for such a narrow filter, but it worked great when I was tuning my BPF.

[Paul_VKHN]

Informative as always Charlie, thanks! I was wondering if the veroboard would introduce capacitance by virtue of the parallel conductors. Soldered pigtails to the end of adjacent tracks and measured 4 pF. Wonder if this is material at 8MHz? Best way to tell would be to make up a second filter ugly style and compare. Probably not worth doing but an interesting thought! 73 Paul VK3HN

[scharkalvin]

can't you use a frequency counter to match the crystals?