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Re: iPhone camera adapter, receive but no send?
Haha! That’s an EFHW I built using a tiny transformer and some 26lb steel fishing line. It’s spooled so I can deploy it quickly and has knots at each band so I know where to clip the pigtail.?
Works pretty great! That day I had about a 1.5-1.6 SWR the entire time I was transmitting.? |
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Re: Higher SWR Dummy Loads ??
On 27/02/2025 14:55, Stig oz8pz-oz8wsp-oz8wsr via groups.io wrote:
o get a swr 2, just use a T bnc and put 2 dummy load on it, then they willAnd note that each of those ways will have a different effect on the PA. You could make different SWRs by adding L and C all giving different loading conditions with a SWR of 2.0 73 Alan G4ZFQ. |
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Re: Higher SWR Dummy Loads ??
开云体育This is simple, make several soda water dummy loads.Here is Mine. I made mine 1 to 1 SWR. it is dead flat from 160 thru 2 meters.? Probably Higher, but don't know because don't have equipment any higher. 1500 watts+ into it with mo problems also. Costs Nothing. Made simple, the two wires are 12 ga copper, about 6 inches long.? Open at the far end. Simple center conductor goes to one wire, Braid to the other. Fill jar with water. Measure SWR. It WILL have a SWR.? If the SWR is what ya want youre done. Naturally the impedance will be higher than 50 ohms. Add tiny amounts of baking soda to the water, make sure it is fully mixed, even wait a while to ensure it is completely dissolved. and measure again. the impedance will have dropped. Keep adding till you get what ya want. only do TINY amounts. it is very easy to overshoot what you want. If you do simplay dump out some solution and add plain water to dilute it some. simple... I haven't tested this idea, of making it variable impedance by varying the amount of water, in the jar, or varying the amount the wires are inserted into the solution.? I think it might make it impedance variable? Joe WB9SBD On 2/27/2025 8:26 AM, Greg McCain via
groups.io wrote:
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Re: Does L502 cause excessive voltages on the QMX finals?
On Thu, Feb 27, 2025, at 06:16 AM, Jerry Gaffke wrote:
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Jerry,
The model you posted does not include the 100pF capacitor across the inductor that acts as a second harmonic trap.
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I also got different inductance values from Toroids.info for the transformer windings.? If you use the info from that site and do the 3:2 windings for 12-volt operation, there is almost twice the power difference without L502.
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73
Evan
AC9TU
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Re: Higher SWR Dummy Loads ??
开云体育Hi to get a swr 2, just use a T bnc and put 2 dummy load on it, then they willbe in parallel, 25 ohm. The other is to put 2 dummy load in serie, but that is not so easy, to get 100 ohm. 73, oz8pz Stig Sendt fra min iPad Den 27. feb. 2025 kl. 15.27 skrev Greg McCain via groups.io <gamccain50@...>:
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Higher SWR Dummy Loads ??
I'm hoping the smarter folks here can help me create some dummy loads with higher SWR's.
I'd like to do some temperature delta measurements without putting signals on the air since I want to include some high duty cycle scenarios at the typical 4-5 Watts outputs of my QMX's and QDX's.
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I Googled this idea but only got hundreds of hits on the general topic of SWR.
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Perhaps SWR's of just 2 and 3.
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I think I should limit it to those values just because there is plenty of evidence that even short bursts of TX into very high SWRs or open loads is a generally bad idea without super fast protection built into the TX circuit chain.?
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Thanks in advance,
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GREG? KI4NVX
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Re: Does L502 cause excessive voltages on the QMX finals?
Attached is a revised LT-Spice simulation of the QMX final, also placed under KE7ER under files.
There are four separate instances running simultaneously allowing waveforms to be easily compared.
T501 is assumed to be perfect, and wired for 9v.? I doubt the 9v T501 matters much in comparing topologies.
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I am now using Evan's SPICE model for the BS170, have two sets of two in parallel.
Now using L508 and L512 reference designators instead of L1, L2.
Corrected the value of C515 from 580pF to 680pF.
None of that made much difference in the simulation.
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The four instances are:
1)? QMX Stock Final.??
2)? Same as above, but removed L502
3)? Same as above but replaced the LPF with a series LC filter with a Q of 3, should be a VMCD topology.
4)? Same as above but removed T501 center tap and added two L502's, now an LC parallel filter, should be CMCD topology.
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There would be tradeoffs in moving to any of these schemes.
Clearly the LC filters would need to be improved on my VMCD and CMCD instances.
Bringing this closer to a true VMCD implementation does reduce Vds-max considerably as expected
though the CMCD implementation has a Vds-max not far from that of the stock implementation.
The CMCD has the most power out of any.
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We could simply recommend that everyone build for the 9v power supply, that may cure most of the issues
with BS170's getting blown from over-voltage.? However, that would increase BS170 current, and may
cause more failures during high duty cycle operation in digital modes from over-heating.
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Here's the math (in python) I used in calculating a Q of 3 for the simple serial and parallel LC filters:
from math import pi, sqrt
Q=3; R=50; w=2*pi*3.57e6;? Cs=1/(w*R*Q); Ls=1/(w**2*Cs); print(Cs, Ls)? ? ?# Serial LC values Cp=Q/(w*R); ? Lp=1/(w**2*Cp); print(Cp, Lp)? ? ? # Parallel LC values Qs=sqrt(Ls/Cs)/R; ?Qp=sqrt(Cp/Lp)*R; ? print(Qs, Qp)? # Double check ?
Jerry, KE7ER |
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Re: Has anyone built the 10 watt PA kit and used it with the QMX?
Ta1mHS
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The 10W amp was designed for lower drive levels.? For a QMX to do that
and not sacrifice anything There is a need need to attenuate its output
by roughly 20db.? To me a waste of power.
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Since the 10W amp is only that all of the switching for RX and TX needs to
be created and that would also include low pass filter.
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Generally using that amp at the output of a radio that does
3-5W is barking up the wrong tree.? IT also does not increase the
power enough to be significant (20W wold be a marginal increse)..
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--
Allison ------------------ Post online only,? direct email will go to a bit bucket. |
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Re: Recommendations for solder temps and workstation
On Tue, Feb 25, 2025 at 07:12 PM, Jerry Gaffke wrote:
I bought this soldering iron and I love it! 100 Watt. Heats quick and gets hot enough for most work you will have doing kits. I would also suggest looking into getting some good tips for it. I found these to be excellent.
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Dean - KC9REN?
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Re: Does L502 cause excessive voltages on the QMX finals?
I suspect the topology is wrong on the QMX for a Voltage Mode Class D (VMCD), L502 simply should not be there.
Since it is there, it is forcing a constant current into the final, creating the voltage spikes observed by KB1NLW in post 136435.
The LPF should present a high impedance to harmonics (especially odd harmonics), so the voltage from the transformer can be a square wave.
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An alternative is Current Mode Class D (CMCD), where we no longer use the T501 center tap and have two L502's.
The LPF should short to ground the harmonics and pass the fundamental, allowing the current from the transformer to be a square wave.
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My guess is that the LPF does not behave appropriately for either VMCD or CMCD.
Perhaps a hybrid of the two was found to work best given the need to cover so many bands with so few LPF's.
One possible path forward might be to keep the current design for those that want all bands from 160m to 6m,?
but have an alternate build supporting only 6 bands where each LPF can be optimized for the frequency of interest.
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I'll run a few more simulations, using a series LC instead of the LPF for VMCD, and a parallel LC for CMCD.
Will use Evan's BS170 model, though I suspect the 2n7002 was close enough for the simulation.
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Thanks to both of you for responding.
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Jerry, KE7ER |
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Re: Does L502 cause excessive voltages on the QMX finals?
Hi Jerry, and GM Evan,
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Evan is correct in all the points he made. Also note that the .asc file he provided includes a model for the BS170 transistor.
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There is possibly a way to create an L502 inductive spike in QMX, but not in the same end-of-transmission way that QDX is susceptible. In QMX the envelope shaping modulator protects against that possibility, if it is functioning properly.
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In QMX an inductive voltage spike might result from a rapid change in load impedance , for example when an ATU is searching for best match and undergoes a big transition. The PA current would try to change rapidly and L502 would respond with an Ldi/dt kick. I have not seen that happen physically but it can be seen in simulation.
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JZ KJ4A?
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Barb WB2CBA
rsmith
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