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Re: Making a Q-meter /
Can you do a 3db Q measurement on the DUT. Set resonance a 1 unit then raise and lower the frequency until the meter reads 0.707 and record the frequencies.
High frequency minus low frequency = xxx then resonant frequency divided by xxx = Q Just wondering what the real Q is. ????????????????????? Thanks, Mikek |
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Re: Making a Q-meter /
John, what are the low and high frequency rolloff points of your 50 to 1 #43 material transformer?
?Is some of that missing 50 points of Q, caused by the loss in the transformer primary? ?What is the Q of your 50Ω primary What do you think are the other losses? ? ???????????????????? Thanks, Mikek |
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Re: Making a Q-meter /
On Sat, Sep 17, 2022 at 06:26 AM, Jeff Green wrote:
https://xdevs.com/doc/HP_Agilent_Keysight/HP%204342A%20Operating%20%26%20Service.pdfHey Jeff, There is a more complete service manual on the Bama site. I had to download a djvu reader to open it, but once I did that, it's pretty nice! This reader is what I downloaded. ??????????????? Mikek |
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Re: Making a Q-meter /
I think you need to consider what happens at DUT resonance and either side of it.? Assume an ideal 50:1 turns transformer.? At DUT resonance, the impedance presented to the 1 turn will be approximately the series loss resistance of the tuned circuit, say 1 Ohm as suggested by Mikek, or 2500 Ohms at the input of the transformer.? Off resonance, the impedance presented to the 1 turn will be capacitive or inductive with a tiny series resistance, depending on whether the frequency is below or above resonance.? The impedance presented to the amplifier will be very high, shunted by the 75 Ohm resistor in the HP circuit to provide a manageable load for the power amplifier under all tuning conditions.? The behaviour of a real transformer will be somewhat different with stray capacitance and frequency dependent leakage inductance.
A while ago I modelled a variant of the HP impedance converter circuit in LTspice using 2N3866 rather than 2N5109 transistors for both Q1 and Q2.? I believe the model for the transistors was reasonably good at these frequencies, but the 2N3866 has multiple emitter connections for low parasitic resistance. The theoretical output impedance was about 0.75 Ohms 200kHz to 10MHz, rising to about 1 Ohm at 50MHz.? Unfortunately I never measured the impedance of the development breadboard as it worked more than well enough for my purposes. PeterS??? ??? G8EZE |
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Re: Making a Q-meter /
Hi Mikek,
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An example of a high Q device measurement is shown in: look for "DUT = R40C1 36T 330/46 with 330pF C0G" Unfortunately my RF voltmeter prototype reads high. A preferred evaluation would be with a HP-400E. There will be loss. Attached is a SimSmith model. For a Q=1000 DUT, measured Q is 935. Error is based on a source generator with 50 ohm Zout. Change Zout to 5 ohm, measured Q will be 950. John KN5L On 9/17/22 5:33 AM, Mikek wrote:
Thanks Steve for setting that up and testing. |
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Re: Making a Q-meter /
Thanks Steve for setting that up and testing.
This discussion for me, is to try to understand how HP built their transformer, I think knowing what impedance drives it is part of that understanding. (it's remarkable to get such a wide frequency range and low impedance) My understanding and I'm saying it out loud so my thinking can be corrected. First the transformer will reflect back the load it sees, as the 4342A measures series resonance, this load could be under 1Ω. My only reference is high Q BCB coils, say Q= 1300 at 1MHz, about 1500Ω reactance, so 1500/1300 =1.15Ω. (I know the 4342A design is for Q=1000, but can be made to measure higher) Any chance to see to see a loss resistance any lower than that? Let's call it 1Ω, reflected back, that would be 2500Ω on the primary, driven by an amp with a few ohms output impedance. ?Corrections and Discussion? |
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Re: Making a Q-meter /
If one performs a more detailed analysis, a good approximation for the output resistance should be:
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(rb2/beta2) + re2 + (1/gm2) + ESR I don't know the parasitic resistances of the transistor, unfortunately, so I'm forced to guess. But a good RF transistor should not have large base resistances. I'll make up a number, 25 ohms, which is higher than I think is reasonable, partly to compensate for neglecting Q1's contribution to the base resistance of Q2 (a few ohms). For beta2, I'll use the universal guess of 100, so the first term contributes 0.25 ohms. You can substitute your own values in the equation above. The parasitic emitter resistance should similarly be small; I'll conservatively guess 0.25 ohms for the 2N5109. The actual value is likely half that. At a current of 84mA, 1/gm2 is around 0.3 ohms. You measured a capacitor ESR of 0.26 ohms, so adding up all the terms gives us a grand total of an ohm or so. Closer to your measured value, but... --Tom -- Prof. Thomas H. Lee Allen Ctr., Rm. 205 350 Jane Stanford Way Stanford University Stanford, CA 94305-4070 On 9/17/2022 00:01, Tom Lee wrote:
And the polarity of the input cap, too, of course... |
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Re: Making a Q-meter /
Despite my attempted analysis of the Impedance converter, doesn't it's output impedance have to be about 2.5Ω? Isn't the 0.001Ω output impedance because it has transformed the Impedance Converter by 2500:1 through transformer action?
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John On 9/16/2022 5:44 PM, Mikek wrote:
Someone sent me a private messaged and corrected me on the output impedance of the 50 to 1 transformer, |
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Re: Making a Q-meter /
And the polarity of the input cap, too, of course...
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-- Prof. Thomas H. Lee Allen Ctr., Rm. 205 350 Jane Stanford Way Stanford University Stanford, CA 94305-4070 On 9/16/2022 23:56, Tom Lee wrote:
I believe that the 1854-0332 is a 2N3866A; your 2N5109 should indeed be a very reasonable choice here. |
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Re: Making a Q-meter /
开云体育I believe that the 1854-0332 is a 2N3866A; your 2N5109 should indeed be a very reasonable choice here.That still leaves us with an order of magnitude discrepancy in output resistance. By any chance, are you powering your breadboard circuit off of a positive supply? If so, did you reverse the polarity of the output cap? And is your circuit soldered together, or are you using a solderless breadboard? --Tom -- Prof. Thomas H. Lee Allen Ctr., Rm. 205 350 Jane Stanford Way Stanford University Stanford, CA 94305-4070 On 9/16/2022 22:44, Steve Ratzlaff
wrote:
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Re: Making a Q-meter /
开云体育Q1 (input) is HP 1854-0091--no "2Nxxxx" equivalent transistor listed in HP equivalent list. Q2 (output) is HP 1854-0332, again no equivalent transistor listed. Both are TO-5/TO-39 case. I think a 2N5109 is a reasonable choice for trying the circuit in the breadboard. Steve On 9/16/2022 10:18 PM, Tom Lee wrote:
Thanks for checking that, Steve.? Unless the 2N5109 has a surprisingly high parasitic emitter resistance, there's still about a 10x gap to be closed. |
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Re: Making a Q-meter /
开云体育Thanks for checking that, Steve.? Unless the 2N5109 has a surprisingly high parasitic emitter resistance, there's still about a 10x gap to be closed.--Tom -- Prof. Thomas H. Lee Allen Ctr., Rm. 205 350 Jane Stanford Way Stanford University Stanford, CA 94305-4070 On 9/16/2022 22:14, Steve Ratzlaff
wrote:
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Re: Making a Q-meter /
Your analysis is spot on (well done for an FPGA designer!); it's the same as that in my first post, although I used 100 for beta of both transistors. In any case, the intrinsic output impedance is very low. The actual output impedance will be dominated by parasitic resistances. For the 2N5109, I would guess emitter resistances of a few hundred milliohms. That would be in series with whatever ESR the output cap possesses. Overall, I would expect something under an ohm. Measurements much greater than that would lead me to check the capacitor, wiring parasitics, and VNA cal.
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--Tom -- Prof. Thomas H. Lee Allen Ctr., Rm. 205 350 Jane Stanford Way Stanford University Stanford, CA 94305-4070 On 9/16/2022 22:04, John Kolb wrote:
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Re: Making a Q-meter /
开云体育And the output capacitor I used was 100 uF/25 volts, with measured 100 kHz ESR of 0.26 ohms. Steve On 9/16/2022 10:00 PM, Steve Ratzlaff
via groups.io wrote:
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Re: Making a Q-meter /
Googling Output resistance of an emitter follower, I find it's input resistance divided by (Beta + 1) plus some other factors, internal emitter resistance of Q2, etc, that I as a FPGA designer couldn't understand. Beta of a darling configuration is the beta of Q1 times beta of Q2. 50 ohm Rin (R1, R2, R3 in parallel) /(100 (beta of Q1) * 30 (beta of Q2)) would be 0.018 ohms. Beta numbers are SWAG. Would a real analog engineer speak up here? At any rate, the output resistance would seem to be much lower than R5, 220 ohms, or 75 ohms, R1 of transformer.
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Would really like to read the complete manual for the 4342A. John On 9/16/2022 5:51 PM, Mikek wrote:
I'm not sure I agree, the schematic I posted shows a 75Ω resistor across the transformer as Zo. |
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Re: Making a Q-meter /
开云体育As noted, first test was at -40 dBm. I raised the level just now to max, -17 dBm--very little change from before--the output impedance decreased about 0.03 ohms for each frequency. Steve On 9/16/2022 8:55 PM, Tom Lee wrote:
Those numbers have a believable trend, but the magnitudes seem too high. I don't know what the parasitic emitter resistance is of a 2N5109, but I would be surprised if it were bigger than an ohm. The output capacitor's ESR adds to that, of course, but a good cap shouldn't have several ohms of ESR. So, if you include realistic parasitics, the output resistance should be an ohm or less. The milliohms number I gave earlier is the ideal value you would get in the limit of no parasitics. |
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Re: Making a Q-meter /
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Those numbers have a believable trend, but the magnitudes seem too high. I don't know what the parasitic emitter resistance is of a 2N5109, but I would be surprised if it were bigger than an ohm. The output capacitor's ESR adds to that, of course, but a good cap shouldn't have several ohms of ESR. So, if you include realistic parasitics, the output resistance should be an ohm or less. The milliohms number I gave earlier is the ideal value you would get in the limit of no parasitics. |
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Re: Making a Q-meter /
开云体育Those numbers have a believable trend, but the magnitudes seem too high. I don't know what the parasitic emitter resistance is of a 2N5109, but I would be surprised if it were bigger than an ohm. The output capacitor's ESR adds to that, of course, but a good cap shouldn't have several ohms of ESR. So, if you include realistic parasitics, the output resistance should be an ohm or less. The milliohms number I gave earlier is the ideal value you would get in the limit of no parasitics.How large an excitation are you using to probe the output Z? Tom -- Prof. Thomas H. Lee Allen Ctr., Rm. 205 350 Jane Stanford Way Stanford University Stanford, CA 94305-4070 On 9/16/2022 19:48, Steve Ratzlaff
wrote:
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Re: Making a Q-meter /
开云体育I breadboarded the circuit just now using 2N5109's and swept the output Z with the DG8SAQ VNWA, 10 kHz-30 MHz. The circuit draws 117 mA; the output transistor draws 84 mA. The output impedance is mostly flat, gradually rising after about 10 MHz. 50 kHz 4.23 ohms 1 MHz 4.42 ohms 10 MHz 5.27 ohms 20 MHz 6.80 ohms 30 MHz 8.77 ohms Steve AA7U
On 9/16/2022 5:44 PM, Mikek wrote:
Someone sent me a private messaged and corrected me on the output impedance of the 50 to 1 transformer, |
John Kolb