Amazing, I'm doning electronics my story is the same.

@SolderSmoke Bill - you nailed it! I'm one of the folks that your and Alan's back and forth has been helping - thanks to both of you! 73

I heard "N2CQR", oh! That's Bill Meara of Solder Smoke! Very helpful info, Alan, especially your explanation of the 13 dB attenuator.

Thank you for the confirmation!

Agreed 100% He is an excellent presenter. He presents info in concise detail that is easy to understand.

Maybe I'll write a book when I retire - no time now!

The same here. Now I feel sheepish.

Much better than a CK-722.

@@gordonwelcher9598 Yep. I remember them well!

Probably a calculator app on their smartphone! (I have a HP15C emulator on my iPhone for when I need a calculator away from home).

You've heard the addage that "current always takes the path of least resistance". We'll that's not the most accurate way to state that... It would be more accurate to say that current always takes the path of least *impedance*. For return currents flowing in a ground path, the "least impedance" translates mainly to "least inductance" as the frequency increases. Inductance is minimized when the "loop area" between the forward path of the current (center of the coax in your example) and the ground/shield return path is minimized. Thus, the image/return currents "hug" the region closest to the forward current path. I talk a bit about this in my video on bypass capacitors (ukposts.info/have/v-deo/cXWSiJqaaaOjlGg.html)

@@w2aew Well blow me over with a whisper! :) Somehow I missed that one - probably (cough) bypassed (cough) it because I already knew about placing small caps near to the VCC/VDD rails on my ICs. I've been doing this like a trained monkey since I was a kid with no real appreciation of why. I've been working my way through your stuff and I wish I'd had teachers with your skill at explaining stuff when I was learning back in the 1970s. It's hard to explain the debt of gratitude I feel for all your work! I'm still a little vague on this transmission line stuff since I tend to associate it with RF stuff that I don't personally work with. Of course, as you've pointed out here, the fast edges we're creating with modern chips (heck, I can recall near-chip bypasses back on early CMOS chips) produce masses of RF harmonics off into the multiple Ghz just by the switch time. I forget if it was Rick Hartley or Eric Bogatin who described the experiment but (if you do care to recreate it), I believe the idea was to put an ammeter in the "short" side and another into the long loop. As the fundamental sine wave is swept up into the high audio frequencies and beyond (if I've grasped what they were saying) the current - continues to follow the path of least impedance, so the current in the dead short drops away while the current in the (measurably) longer DC path starts to increase. Presumably this would require the sort of bench gear that many of us don't have as DVMs won't be able to measure AC currents accurately. I think it was Paul at EEBlog who traced around a ground plane with a fairly high end current probe attached to a Tec scope and demonstrated how signals propagated through the copper. I know this is pretty basic stuff to some but my poor brain opened the lid of my noggin and a white flag popped out. ;) Apologies for the humour, it's the shortest path to describe my ignorance and astonishment at these wonderful demonstrations. Thank you again.

Yes, it has to be biased because the feedback helps to set the impedance. A DC block is needed, and is included in the design.

Yes, it was powered up.

Some models don't have the ISOLATION cal, but it should have the Through Cal.

LOL - not sure where it came from, it's been in my accessory box for a while...

You would simply terminate the input of the amplifier, and then connect the output to CH0 and run a S11. But, also you can see this basically from inspection. An emitter follower has a very low output impedance (basically 0.026/Ic), in this case just a few ohms. Then, there is a 47ohm in series - so it's basically very close to 50 ohms.

Terminate the input, connect the output to CH0 and measure S11.

@@w2aew thank you. I assumed there was more to it. But it really is as simple as that I guess.

The affect of the attenuator can be calibrated out. However, since the signal injected to DUT is attenuate, and the reflected signal is also attenuated, there will be some additional uncertainty in the measurement - especially for DUTs with a good S11 (low reflections).

no need to shout here

For a typical diode ring double balanced mixer, the LO port will typically NOT have a nice, well controlled impedance. The function of this port is to quickly and fully commutate the diodes. When this happens, then RF/IF ports should reflect the impedance at the other end, since the diode is making the connection from the IF to RF (or vice versa). Testing the IF or RF ports without a) terminating the undriven port, and b) properly driving the LO port, will lead to incorrect results.

@@w2aew Thank you!

Have you watched these two videos? ukposts.info/have/v-deo/b2SXrm-grpCQ1IE.html ukposts.info/have/v-deo/fpZmrIV8hX91mKs.html

No, the LogMag measures the response level relative to the stimulus (either reflected response or thru response, depending on the channel/port)

As long as the output is AC coupled, then simply terminate the input and measure S11 on the output. I am currently running 1.0.39 from Dislord (see video #320: ukposts.info/have/v-deo/hpOJrn-Lh4aF2nU.html) on my H4.

They are quite different. The LM324 is specified for operation from 3V to 32V supplies, while the TL072 is rated for 4.5 to 40V supplies. The LM324 input common mode includes the negative supply rail (but not the positive supply rail). The TL072 is just the opposite - input common mode range includes the positive supply rail, but not the negative supply rail. The TL072 output can swing fairly close to both rails (with light loading), while the LM324 can only get up to 1.5V below the positive rail. These are just a few of big differences...

@@w2aew Thank you very much for the quick response. I bought last year a TL074 with ST brand(no original) and last month with another brand(no original) but they're both from China. I wondering why the newer one behaves differently, lots of noise and early clipping. I'm thinking I might have some errors. I'm thinking if there are proper ways of using JFET input Op-Amps though my ST brand workes fine on the same circuit. I know the second purchased with another brand are not original for sure but same with my ST brand that works. Maybe I was faked(?) Thanks.

@@JB-20 It sounds like you may have received fake/counterfeit ones. Also, not that not all JFET op amps have the same specifications - so always check the datasheet. Of course, if you get fake ones, all bets are off...

@@w2aew Ok, this clears everything. Thanks a lot.

I'll have to update my firmware to see - not sure how much it can be adjusted.

I didn't calibrate at the end of the adapter because I don't have a set of female open/short/load standards. Not worried about it though, since the phase shift through that short adapter was not significant at the operating frequency of the amp.

@@w2aew Thanks! That makes sense.

If you are looking to measure the impedance of a transmission line on a PCB, you might be able to use this: ukposts.info/have/v-deo/oKF8gHyZhY-Du5c.html

@@w2aew many thanks I will try It out. my line from the tranceiver chip to the antena is 14mm

@@vitorperez3283 That's going to be way too short to characterize with a low cost VNA - you need a much higher frequency unit

@@w2aew the frequency is 2.4ghz

@@vitorperez3283 Understood - but to measure the impedance as I show in the video, the test frequency has to high enough to be about 1/2 wavelength for the line. Instead, you can simply test the antenna system impedance (antenna + line) as seen by the transceiver chip, and do this at the desired operating frequency of 2.4GHz. This will require you to calibrate the VNA at the IC connection point.

If I ever get one, I will!

@@w2aew Ameen....soon 🔜

As described in the video - it drops the level to an acceptable level, and it’s approximately equal to the amplifier gain

Yes, even beyond that with some reduced gain.