Simple SSB Rig: Part 7 - Bandpass Filter

Video looking at a Butterworth doubly terminated two pole BPF.
Note, the -3 dB freqs should be 3 dB down from the passband. As the passband is at approx. 1.2 dB down, another 3 dB would make -4 dB from the top of the screen. That would make the bandwidth around 3550 kHz to 3950 kHz.

[@gordslater]

To solve the reflections on the NanoVNA screen, if the camera has manual or at least +/- adjustable exposure try throwing a white sheet over your head and the camera tripod, like a tent. You might need to improvise a "pole" to keep the lens clear. No lighting inside, the camera should adjust to the screen display. The surroundings and your hands will be dark but at least no reflections (caused by the ceiling and ambient lighting) These vids are absolutely great btw - I've only just found them after a 20+ year hiatus in radio construction. Showing your working and assumptions is really useful for newcomers to design/construction/fiddling

[@shaneqrp]

It looks better than you thought Charlie! I look forward to the next episode.

[@CharlieMorrisZL2CTM]

Thanks Shane. It certainly tuned up well.

[@M0UAW_IO83]

Nice video as always, I've got an R&S analyser which I've used for testing and adjusting filters a few times but I tend to use the NanoVNA now, it's just so much simpler to set up and gives me pretty much the same results, certainly good enough for my needs when I'm homebrewing. Pretty certain -3dB points are referenced to the passband so they'll always be -3dB

[@CharlieMorrisZL2CTM]

The NanoVNA certainly works well. Yes, the -3 dB points are referenced to the passband, but in this case the three markers are referenced to 0 dB (top of screen). The passband is already 1.2 odd-dB down so I'd need to add another 3 dB.

[@curtstacy779]

Looking good Charlie, glad to hear my little toy (nanoVNA) will work well enough for now. lol

[@CharlieMorrisZL2CTM]

It certainly will Curt. I need to update the video description as I realised over dinner that I made a mistake with the -3 dB limits. All good!

[@jerryfankhauser2959]

Thank You Charlie, I love your new "toy" it looks like it could be a pound or two lighter than my old HP8568B. Also I did finish my IF amp with AGC, all surface mount almost burned my eye balls out, I'm 74. WA8HTO

[@CharlieMorrisZL2CTM]

It certainly is light. The HP8568B was the last sig gen i used back in the Air Force. Things have certainly changed! Great news too about your IF amp. I will have to get into SMD at some stage...

[@tautech8196]

Hiya Charlie. Nice to see you making the most of what was our demo SA. When you were adjusting the passband it may have been better to have the 0dB ref level down the display some so to properly see the upper limit of the passband. You can change the reference level in the Amplitude menu. Rob

[@CharlieMorrisZL2CTM]

Thanks Rob. Still learning how to use the SA. Thanks for the tip!

[@anonhollmuller4032]

hey greez! Set the Illumination to max and put uppon it a sheet of backing paper (what you use an prepare pizza, if you want keep out unwanted dirt out of your oven(stove?). rhen will be no reflection at all (dimm the light). ;) Sorry for my poor english ! well done no! you do this perfekt!!! soooo much thx for Inspiration:) 73!

[@Ahmet_Yilmaz]

Attenuation which is below bandpass bandwidth is not identical attenuation which is above bandpass bandwidth. Why is not symmetrical ?

[@joeb3300]

For what Tx power was this designed? Thanks!

[@skylabby]

really enjoying this series charlie, The only module i haven't seen is the antenna amp , have you covered that one already?

[@CharlieMorrisZL2CTM]

As this is a 80m radio (below 10 MHz) I'll look to do away with a antenna amp. I should have enough overall gain.

[@yakovdavidovich7943]

@@CharlieMorrisZL2CTM is there some amount of total gain that you're looking for? What difference does the band make on that? I've only found one book with substantial discussion of total gain requirements for a receiver (EMRFD), and I'm curious if there is some rule of thumb you use.

[@Zeus-ub2zp]

Charlie, Please the connector to the SA, what is it called? BNC Female to N Male RF? Can you kindly provide a link to the one you got Thank you

[@CharlieMorrisZL2CTM]

Hi. It was a N type to BNC.

[@CharlieMorrisZL2CTM]

N type male to BNC female

[@R2AUK]

Might be of interest to compare this BPF vs 7 pole direct coupled resonator filter, like the one calculated by leleivre.com/rf_coupled_resonator_cheb.html or www.iowahills.com/9RFFiltersPage.html

[@CharlieMorrisZL2CTM]

I'll take a look Alex.