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Re: Tank circuits
Transistors and tubes probably too, need a load which is less than the transistors internalHello It is the reverse. Fortunately, in a PA, the impedance of the antenna is not matched to the output impedance of the transistor or of the tube. The efficiency would be catastrophic. In concrete terms, the optimum load impedance that must be applied to the tube or transistor is calculated so that it produces the expected power at the desired frequency. This impedance must be much greater than the internal impedance of the source for the efficiency to remain satisfactory. There are tables for determining the optimal load impedance depending on the voltage, the quiescent current and the class of the PA. If the PA is in class AB push-pull symmetry we could almost do without filtrag at the output. If it is a class B stage with a single tube or transistor, filtering is essential to reduce the harmonics and this is where the difficulties begin. What impedance should be presented to the PA on these harmonics to get rid of them or not to produce them. Not all filters will give the same performance on the fundamental. Getting back to the nanoVNA. You can prepare the filter by mounting it upside down and simulating the load by the calculated resistance with, in parallel, a capacitor representing the output capacitance. The best is to calculate the adapter and to realize it with the calculated values. If a transformer is intercalated it becomes much more complicated to predetermine the components because we cannot measure the characteristics of the transformer at nominal power. Since the transformer is not linear, extrapolating a measurement made with the NanoVNA will lead to large errors. 73 -- F1AMM Fran?ois |
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Re: Tank circuits
On 7/18/23 11:53 AM, W0LEV wrote:
In the older tube transmitter days, the Pi or Pi-L networks thatThe term is *much* older than matching networks. It refers to something holding energy when the tube (or spark gap) is cutoff. An "energy tank" if you will. In a classic Class C power amplifier, current flows through the pass device for a fraction of the cycle (improving efficiency, usually), but you want a continuous sinusoidal output, so you need something to keep the current flowing (or the voltage up) - hence a resonant LC tank. Today, they're probably mostly used in high power RF systems like plastic sealing and the like. Most Vacuum Tube Tesla Coils run the tube in Class C, as well. I think these days, FM and TV uses solid state amplifiers, some of which are effectively a power Digital to Analog converter. But back in the day, Class C gives you great efficiency with constant envelope modulations. And of course, if we step back a bit further to the days of king spark, your tank circuit was periodically excited by a rotary spark gap, giving you a classic damped wave emission. Spark Gap tesla coils are much the same, except they don't have a big antenna attached, and often are also a transformer to higher voltages. But anyway, a VNA is a fine way to adjust them. |
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Re: Tank circuits
Transistors and tubes probably too, need a load which is less than the transistors internal resistance. But to get maximum power out of the device, you much lower load impedance. So, what does the VNA show then.
I am trying to say that at least with transistors, the collector current does not depend on the collector voltage (within limits). That is the same as high impedance. But the optimum load is much less. Class C RL=UCC*UCC/(2*POUT) |
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Re: Tank circuits
I also add a parallel capacitor to simulate the tube output capacitance.
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Mike
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Re: Tank circuits
Dave's response suggests an interesting variation. I was going to say, what do you use as the source impedance (plate impedance)?
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And an obvious answer. Tune up ytansmitter in dummy load (540 ohms) as usual, for maximum loading or desired RF power out. Then turn amplifier off, remove HV. Put VNA on output in place of dummy loand. Put a variable (sort of) non inductive resistor from plate cap to ground, and adjust resistor for best 50 ohms on VNA> Or possably a series of carbon fixed resistors until you get close. You may need a small variablr C across thr plate equivalent resistor to get to VNA dead center. Then you know Plate (Source) impedance. Lester B Veenstra K1YCM M?YCM W8YCM 6Y6Y W8YCM/6Y 6Y8LV (Reformed USNSG CTM1) lester@... 452 Stable Ln Keyser WV 26726 USA GPS: 39.336826 N 78.982287 W (Google) GPS: 39.33682 N 78.9823741 W (GPSDO) Telephones: Home: +1-304-289-6057 US cell +1-304-790-9192 Jamaica cell: +1-876-456-8898 -----Original Message-----
From: [email protected] [mailto:[email protected]] On Behalf Of W0LEV Sent: Tuesday, July 18, 2023 2:54 PM To: [email protected] Subject: Re: [nanovna-users] Tank circuits In the older tube transmitter days, the Pi or Pi-L networks that transformed the plate impedance (in the 1000's of ohms) to nominally 50-ohms were referred to as "tank circuits". The term has carried over in some instances. These days with solid state finals, there are no resonant "tank circuits" to do the transformations. Wide band ferrite loaded transformers serve that purpose. Dave - W?LEV |
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Re: Tank circuits
With today's solid state finals, BJT or FET, there is no "resonant" circuit
between the collectors or drains and the 50-ohm port. Consequently, there is no "tank circuit". The transformation is accomplished with wide-band ferrite loaded transformers - nothing resonant. Following that transition, however, there are LPFs to eliminate higher-order harmonics and possibly spurs to be in compliance with regulatory agencies. But there is nothing truly resonant in any respect with the modern solid state finals. However, even the modern tube linear (if operated properly) amplifiers still employ a resonant and tuned "tank circuit" to match the plate impedance to 50-ohms. That usually takes the form of a Pi or Pi-L circuit. Dave - W?LEV On Tue, Jul 18, 2023 at 7:31?PM Siegfried Jackstien < siegfried.jackstien@...> wrote: But tuning is done same way.. Replace tube with your calculated impedance-- *Dave - W?LEV* -- Dave - W?LEV |
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Re: Tank circuits
Never do that with hot circuit!!!
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But replace tube with a few kohms resistor... And then do a cold tune Dg9bfc sigi Am 18.07.2023 21:35 schrieb "Lester Veenstra via groups.io" <m0ycm@...>:
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Re: Tank circuits
And I am too chicken to put a VNA on the output if that PiNet "Tank" with the tube active
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Lester B Veenstra K1YCM M?YCM W8YCM 6Y6Y W8YCM/6Y 6Y8LV (Reformed USNSG CTM1) lester@... 452 Stable Ln Keyser WV 26726 USA GPS: 39.336826 N 78.982287 W (Google) GPS: 39.33682 N 78.9823741 W (GPSDO) Telephones: Home: +1-304-289-6057 US cell +1-304-790-9192 Jamaica cell: +1-876-456-8898 -----Original Message-----
From: [email protected] [mailto:[email protected]] On Behalf Of W0LEV Sent: Tuesday, July 18, 2023 2:54 PM To: [email protected] Subject: Re: [nanovna-users] Tank circuits In the older tube transmitter days, the Pi or Pi-L networks that transformed the plate impedance (in the 1000's of ohms) to nominally 50-ohms were referred to as "tank circuits". The term has carried over in some instances. These days with solid state finals, there are no resonant "tank circuits" to do the transformations. Wide band ferrite loaded transformers serve that purpose. Dave - W?LEV On Tue, Jul 18, 2023 at 4:55?PM Zack Widup <w9sz.zack@...> wrote: Yes, I have done this quite a few times.-- *Dave - W?LEV* -- Dave - W?LEV |
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Re: Tank circuits
But tuning is done same way.. Replace tube with your calculated impedance (a few kohms for tube or low ohms for a power fet)... And then tune that inpedance matching unit/tank circuit to resonance and match..
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You either transform 2kohm to 50...or just a few ohms (2 to 5 maybe) to 50 ....in fact a tank circuit.. Or an antenna tuner...are basically the same thing. Dg9bfc sigi Am 18.07.2023 20:53 schrieb W0LEV <davearea51a@...>:
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Re: Tank circuits
In the older tube transmitter days, the Pi or Pi-L networks that
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transformed the plate impedance (in the 1000's of ohms) to nominally 50-ohms were referred to as "tank circuits". The term has carried over in some instances. These days with solid state finals, there are no resonant "tank circuits" to do the transformations. Wide band ferrite loaded transformers serve that purpose. Dave - W?LEV On Tue, Jul 18, 2023 at 4:55?PM Zack Widup <w9sz.zack@...> wrote:
Yes, I have done this quite a few times.-- *Dave - W?LEV* --
Dave - W?LEV |
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Re: Tank circuits
Not sure that the initial tank referred to, although a VNA will measure a stand along tank (L and C in series or parallel across the terminals) just fine.
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Although "Tanks" have a place in antenna matching, in reality all that actually required in amateur applications is some form of two component ( L and C) "L" configuration . For example ; most antennas can be matched with a PI Net configuratiuom. But if the PI net has a continuously variable L ( roller inductor ) than you can always match with either the input or ourput parallel C, set to zero, reducing the "Pi" to an "L" configuration. The position of the C element to ground, on either the input or output side depends on the antenna unturned impedance being more or less than 50 ohms. Lester B Veenstra K1YCM M?YCM W8YCM 6Y6Y W8YCM/6Y 6Y8LV (Reformed USNSG CTM1) lester@... 452 Stable Ln Keyser WV 26726 USA GPS: 39.336826 N 78.982287 W (Google) GPS: 39.33682 N 78.9823741 W (GPSDO) Telephones: Home: +1-304-289-6057 US cell +1-304-790-9192 Jamaica cell: +1-876-456-8898 -----Original Message-----
From: [email protected] [mailto:[email protected]] On Behalf Of Fran?ois Sent: Tuesday, July 18, 2023 1:43 PM To: [email protected] Subject: Re: [nanovna-users] Tank circuits What is "tank circuits" for an antennas ? Are all "RF Impedance Matching" "tank circuits" ? -- F1AMM Fran?ois |
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Re: Tank circuits
Yes, I have done this quite a few times.
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Zack W9SZ On Tue, Jul 18, 2023 at 11:52?AM Ma?l H?rz <mh-nexus@...> wrote:
Hello, |
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Re: YouTuber channels claimed as the same, but dont seem to
On Sun, Jul 16, 2023 at 07:49 AM, Ma?l H?rz wrote:
I might be wrong, but from voice and hands I would say those twoFrom the level of skill and knowledge in certain areas, and from the equipment they have on hand, I would have to agree: they are definitely NOT the same person. |
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sd card implementation
I possess a nanoVNA-H4 with HW version 4.2.1 (printed on the PCB inside), bought at about the midst of 2021 from alibaba.
There are already solder points on the board for the implementation of a sd card socket. I want to ask whether I have to implement/change some additional hardware components or wires to successfully integrate the sd card. In addition I want to know the firmware version I have to update for a successful integration of the sd card. My current running software version is 1.2.00 [p:401, IF:12k, ADC:384k, Lcd:480x320] Architecture: ARMv7E-M Core Variant: Cortex-M4F Platform: STM32F303xC Analog & DSP TCXO = 26.000 000 MHz In addition my date and time is not working correctly. What do I need to change/implement? |
Jim Allyn - N7JA
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