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QMX+ Military Version
Okay, I went a little crazy being a military radio guy the standard QMX case just wasn't doing it for me.? So I decided to draw up a PRC-174/CMX+ clone using Fusion 360 CAD software and my 3D printer. The radio isn't fully functional yet like the 6 holes above the LCD are for an LED voltmeter using an Ardunio Nano, and the custom built battery which will reside in the back section. The CMX board is located in the front half of the case unfortunately I wasn't able to print the case in one piece since my printer bed wasn't large enough I think the case looks okay in two pieces. For those that don't know what a PRC-174 is check out N6CC.com or RadioNerds.com site under PRC-174.
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73, Dave
W6MQI
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Re: QCX buzzing sound on key down
Thanks. It does it with a known good power supply into a dummy load sometimes. Sometimes it works for a few minutes. It’s in a die cast box with a 0.1 uF across the power connector and the power cable loops through a large ferrite. The antenna jack is fed with RG 174. It did work before. I will look some more when I get time.
-John? |
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Re: QMX IQ Sweeps
Stan, I’ll try attaching the images again in a few minutes, but I don’t think that will help. Even when I use my wife’s computer, I can still see the images so I think there may be a problem with the images external to me.
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You make a very valid point about why worry if it’s working ok. I thought about that but it bugs me knowing something is wrong and I just want to figure it out. |
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Re: QMX IQ Sweeps
After another look at the schematic, I see no reason to lift the RX_IN wire of L401
or the IC402-9 wire of T401.? Just shorting those wires to ground should be sufficient.
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RX_IN might see 12vdc through R510 and Q508, but R510 is 470k so the current will be miniscule if RX_IN is shorted.
IC402 and IC403 are just analog switches, they do not have drivers and receivers inside.
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I suggested you put a 50 ohm dummy load on the antenna port to ensure the noise source is not external.
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Jerry, KE7ER
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On Mon, Feb 24, 2025 at 03:40 PM, Jerry Gaffke wrote:
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Re: QMX IQ Sweeps
Matthew, your original screenshots of the IQ plots did not come through.
Maybe if you show us the screenshots it will give us some ideas to help you with.
And if "everything works fine", is there a reason why this is important to fix? meaning does it interfere with good reception or signal decoding, or reduce receive sensitivity or clarity?? Or is it just a mystery that you want to find?
Stan |
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Re: QMX IQ Sweeps
What kind of power supply are you using???
Try running off a 9v transistor radio battery, or something else reasonably quiet.
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Do you have a 50 ohm dummy load at the antenna port when testing?
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I'd try cutting the receive chain in various spots.
For example, try lifting the RX_IN wire of of L401, and tying that wire to the ground plane.
If the noise has gone then the problem is back in the transmitter LPF section somewhere and subject for another post.
Should be able to tie 20 feet of magnet wire to that L401 wire and hear some signals.
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If you still have noise, try lifting the T401 wire that goes to pin 9 of IC402 and tie that wire to ground.
If you still have noise, try shorting across C416,417,419,419 so all four inputs to the LM4562 op-amps are grounded.
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If you still have noise you might short across C426 and also C427 so the left and right differential signals
into the PCM1804 are zeroed, but first check with a voltmeter that there is no significant voltage
across those caps or you may blow the op-amps.
Assuming C416-419 are still grounded, I would expect no voltage across those caps.
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Jerry, KE7ER
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On Mon, Feb 24, 2025 at 03:07 PM, Matthew Basanta - NE3U wrote:
I’m bumping this to see if there are any more ideas. I’ve checked everything I can think of. I rewound T401 (the trifilar toroid) and replaced the PCM1804. I’ve followed the audio chain through the receive section with my scope but can’t identify a specific issue. I’m at the guess and check stage and looking for ideas. It’s picking up noise somewhere but I have no idea where. |
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Re: QMX IQ Sweeps
I’m bumping this to see if there are any more ideas. I’ve checked everything I can think of. I rewound T401 (the trifilar toroid) and replaced the PCM1804. I’ve followed the audio chain through the receive section with my scope but can’t identify a specific issue. I’m at the guess and check stage and looking for ideas. It’s picking up noise somewhere but I have no idea where. |
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QCX+ 30M for Sale
开云体育?? I have a factory built 30 Meter QCX+ for sale, $80 shipped USA, contact me by my QRZ email. ?????????????????????????????????????????? W6TOM |
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Re: Poor Mans ESD Safe Work Surface
Oh completely understand.
toggle quoted message
Show quoted text
I don't actually use that worktable for actual power on testing. At most, I ohm out detailed checkpoints or other ohmic confirmations of connections. If I've removed the board from the holder to do those sorts of checks, I place it on top of another non conductive surface ( manilla folders are my friend for lots of tasks).? Any power on testing I do at my shack operating tables. You are correct. The mats are nice.? Just an old habit of mine from way back in the day before there were such things outside of pricey commercial sources. I think I picked it up on list of hints and kinks documents that Elecraft had in its website back when it was all kits and I built out a K2.? GREG
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Re: Poor Mans ESD Safe Work Surface
I prefere a non conductive esd mat. The mat and wrist strap have resistors in. I also use a plug with just the earth connected and not had any issues in 25 plus years(apart from replacing the strap every so often ). On Mon, Feb 24, 2025, 8:38 PM Stan Dye via <standye=[email protected]> wrote:
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Re: QMX kit arrived w/damaged L501, is it a problem?
Maybe it is regional... My QMX+ kit arrived today in PERFECT condition. No damage to the outside packaging. The 1st thing I checked was L501: AOK inside an anti-static bag, inside a paper envelope, inside a cardboard box, and the FED-X plastic envelope.? So.... to this southeastern corner of the USA, a happy result.? FED=X people here are careful.?
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72 de N4REE, Bob Easton - QRP CW forever |
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Re: QMX Rev 4 Schematics
Andy,
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With that current draw, there is very likely something shorting or not connected properly on your board - this is much more common than a component failure, especially capacitors which rarely fail (but could have poor soldering).
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Since you feel the 5.6V zener getting hot, it means it is sinking power, which it does to protect the output of the 5V supply from going too high in voltage.? This can happen for a few reasons: 1) the 12V bus is shorting somewhere to the 5V bus; 2) there is a short somewhere on the 5V bus; 3) the ADC_5V signal is not getting to the processor properly; 4) some other less likely smps or component fault.? Since you measured that VCC is following the 12V rail, the first of these is likely your problem.
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It would be wise to reduce the current limit of your power supply to 250mA while you finish troubleshooting, as it is less likely to damage something.
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So I would check again very carefully for solder whiskers across the board, and for other possible shorts.? If you remove your 5V SMPS and measure the resistance between the 5V pin and Gnd on the main board, you should see a resistance of a few K-ohms - if it is less, you need to check for shorts on the main board, otherwise the problem may be on the SMPS or the interconnect.? There is a good entry on the wiki of this group about independently testing the SMPS boards for issues: /g/QRPLabs/wiki/37128
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Your 3.3V supply and processor are likely working ok, otherwise the 5V wouldn't even be on.
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Regarding the SMPS from your other units:? they are fundamentally the same, but there have been a few updates: 1) relocations of components, to avoid soldering and assembly issues; 2) sometime after original smps, another resistor R115 was added to reduce the voltage on the LIN_REG_EN pin - this is not critical, and is not in the QMX+ design; 2) the 5.6V zener was changed from a small 0.5W part to a much larger 5W part.? So if your other SMPS do not have the larger zener, I would not use them on this unit until you make sure the fault is not in the connections or on the main board, since with the fault still present, you may burn out the smaller zener.
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And regarding the QMX schematics, the rev 3 schematics are identical to the rev 4 implementation with one minor exception, which is the wiring of pin 4 on the PTT output connector (which rev 4 moves to pin 2 where it should be).? So you can use them with confidence in debugging the rev 4 QMX.
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Stan KC7XE |
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Re: QCX buzzing sound on key down
John,
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Just checking: when you say that it is a good battery are you measuring the voltage under key down/transmit conditions or just during RX.? When a battery is low, it may measure 12 volts during RX but when the transmitter is keyed the voltage would drop to where it made noises.? ?Just hate to see you tear into the rig if it is something more basic.
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Brien - KE7WB |
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Re: QMX new build showed up as USB but unresponsive after firmware transfer
开云体育Just to clarify, also re-arranged on the top of the board. But no documentation exists for these changes.
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CW Practice / Rag Chew
开云体育On 2/24/25 I had a CW practice / rag chew session on 20 meters. I worked five stations:?
Conditions were good. SSN = 186, SFI = 210, A = 7, K = 3. I will be doing another CW on the air practice session Tuesday?25?February. Anyone is welcome. This practice is intended for operators who are new to CW or they need some practice. IT DOES NOT MATTER HOW POOR YOUR CW IS. Mistakes are OK. Poor fists are OK. Slow speed is OK. Really slow speed is OK. This practice is meant for you to improve your CW. I will do my best to adjust to your skill level. Operate at any power level. If several stations show up, I will operate as a round-table control station. I will do it as a round-table so everyone gets a chance to transmit. Please listen to my directions. Details: Date - Tuesday 25 February Time - 9:00 AM Eastern Time / 14:00 UTC Band - 20 Meters How to find me - I will find a clear frequency and call CQ. Go to the Reverse Beacon Network and search for my call sign AB8DF. That will tell you what frequency I am on. Tune your station to that frequency and if you hear me give me a call. If there is a QSO in progress, please wait for a break in the action. Then send your callsign. If I hear you, I will invite you to join the QSO and start a round-table QSO. Reply to this email if you have questions. IT DOES NOT MATTER HOW POOR CW IS Ed AB8DF |
W6MQI
N4REE - Bob
Brien - KE7WB