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Re: cap values
Surface mount silver mica capacitors exist. You have to step up to the larger 1210 size rather than 0805 to get parts that are rated for 500V; the 0805 ones are only rated for 100V. You're unlikely to encounter silver mica capacitors in ATU100 kits or assembled tuners from China because they are expensive; For example, here is a suitable part from Digi-Key in the 1210 size:?? Those cost $4.23 in quantity one, coming down to $2.65 if you buy 100 or $1.74 if you buy 5,000, but you can't currently buy 5,000 because they don't have that many in stock. The smaller values are a bit less expensive, and prices in China are likely to be lower than US distributor prices, but nonetheless it would be prohibitively costly for the kit seller in China to provide seven of those capacitors in a kit that sells for about $30 delivered. NP0 ceramic capacitors are much less expensive, and they're available in an 0805 package. For comparison, here is the least expensive 500V NP0 capacitor in the 0805 package on Digi-Key:?? That one costs 18 cents in quantity one, 6 cents in quantity 100, or 3 cents each on a reel of 4,000. Those are the kind of parts you're going to find in a kit from China, not the expensive silver mica version. Other brands are more expensive; the next cheapest one that's in stock right now costs 48 cents in quantity one, which is still far cheaper than the silver mica. Will the less expensive ceramic capacitor work? If they have provided high quality ceramic caps, yes. Will losses be as low as the silver mica? Unknown; testing is in order. On Tue, Mar 21, 2023 at 6:19?AM mike <pencoys@...> wrote:
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Re: cap values
¿ªÔÆÌåÓýits a 220pf 500v silver mica according to the circuit diagram its probably a 220pf ceramic in 0805 size from what I observe of
an unbuilt PCB - hth On 21/03/2023 01:33, Paul M3VUV wrote:
ive burned a cap in my atu,see pic,can anyone recomend what i need to replace it with ,ie value and type?,cheers +73 |
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Re: ATU-10: an alternative PCB layout?
Hello Yan, do you mean the pad marked in red in the picture below? I don't think that is the fault, it is just where the braid of the cable going to the TRX is grounded. See the pictures below.
I was wondering if the problem might lie in the HW changes that Anton/ZAO made to the original BOM. In a post lower down in this thread Anton writes: ??? 56,2 Ohm 1% resistor (1206), 2 pcs (to replace the original 50 Ohm ones) ??? 287 Ohm 1% resistor (0603), 2 pcs ??? 787 Ohm 1% resistor (0603), 2 pcs ??? 1nF capacitor (0603), 2 pcs ??? 10nF capacitor (0603), 2 pcs ??? 1uF capacitor (0603), 2 pcs ??? 10uF 16V tantalum capacitor (size A), 1 pcs Also the pair of 47 kOhm resistors (0603, traces between the AD8361 outputs and the FWD, RFL test points) to be replaced with ~100 Ohm ones, or to be shorted alltogether.
There should be 10 turns in the "binocular" windings (instead of the original five turns).
73, Mat¨§j OK2MTB(end of the citation) I honestly have no idea if the increased number of turns on the binocular ferrite (10 instead of 5) must be and is reflected in the firmware. I need to measure the voltages from the detectors on the test points. Can someone please advise me what voltages I should expect there or what voltages are expected by the firmware in the microcontroller? |
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Re: New version of control PCB
#1KW
Hi!
I got the PCB's from JLCPCB yesterday, well done. Programmed right away, tested the drivers passively, with 5V source - they work fine and drive relays much beefier, than the ones I will use in the RF deck. Of course, as it always happens when one forgets to switch off all PCB layers and check for unconnected points, one "string" was forgotten on the PCB. I put a wire on and fixed the PCB files, the GERBER's are attached. I ill next start working on the RF deck. Much thought has to be put in it to minimize stray anything and get the losses to minimum and I'm not sure about ETA for the new design. All the best, guys! Bill LZ1SWE |
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Re: ATU-10 kit or build - newdiytech.com website
Hi?Russell and Marek, For the ones that are not familiar, this is the corresponding document: |
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Re: T match
Very well noted! Actually selection of tuner architecture should lie in the character of the load itself. Sometimes specific loads will cause much losses in T-networks, and some will not be tunable at all with L-networks, requiring massive amounts of capacitance/inductance to transform the impedance successfully back to 50+j0 ohm. This means, that one has to define where in the impedance plane the load lies, and then use the appropriate network to get it home. And this cannot be done using just an reflection bridge and calculating SWR. It actually means absolutely nothing impedance-wise, but it's simple and cheap to measure, so we use it. Ideally one would have 3 detectors - resistance, phase and conductance, so the choice of network topology can be clear and unambiguous - and with the lowest losses for each part of the impedance plane.?
There is a very good set of articles by David Knight about this -?  Going back to the ATU-XXXX series of ... well ATU's... they use only SWR for matching, and while this is acceptable for L-networks, having only one optimal solution for each load transformation, consisting of a single set of L and C values, T-networks have one solution with highest Q and lowest losses, and possibly 5-6 other solutions, which will also transform the impedance to 50+j0, but will waste our precious power as heat up to 60-70% in some cases. One other topology, that has only one optimal solution, that can be detected with just an SWR meter is the Differential-T network, where you have handicapped the T-network, by tying together the two capacitors in one differential (butterfly) variable capacitor. This robes one of the degrees of freedom from the T-network, but will allow to get only one tuning solution with some losses. Actually all popular networks are very well described in Part 2 of the above article - enjoy! |
va3rr
Shirley Dulcey KE1L
mike
Billian Marinov
HB9EAJ