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Hi all
I have written an article about the recommended PCB Rev 2 modification that prevents potential destruction of IC402 (74CBT3253 BPF MUX) due to large parasitic oscillations. See?
This modification involves adding a small signal diode (such as 1N4148 but it is non-critical) to the Tx/Rx switch transistor Q508. It is highly recommended for any QMX Rev 2 owner whose kit or assembled radio was shipped during 2023.?
Very important to note: - This modification is NOT required for any QMX Rev 1 PCB... though if you don't read this note and you do it anyway, there will be no harm done.?
- This modification is NOT required for any QMX Rev 2 PCB shipped in 2024, the QRP Labs team are already modifying all PCBs (kit and assembled radios) before shipment.?
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Hi all
I have written an article about the recommended PCB Rev 2 modification that prevents potential destruction of IC402 (74CBT3253 BPF MUX) due to large parasitic oscillations. See?
This modification involves adding a small signal diode (such as 1N4148 but it is non-critical) to the Tx/Rx switch transistor Q508. It is highly recommended for any QMX Rev 2 owner whose kit or assembled radio was shipped during 2023.?
Very important to note: - This modification is NOT required for any QMX Rev 1 PCB... though if you don't read this note and you do it anyway, there will be no harm done.?
- This modification is NOT required for any QMX Rev 2 PCB shipped in 2024, the QRP Labs team are already modifying all PCBs (kit and assembled radios) before shipment.?
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Thank you very much for your advice Hans, I will install the diode as you described.
Giuseppe iu8eun
Il Gio 4 Gen 2024, 10:46 iu8eun Giuseppe Coppoletta < iw8rsb@...> ha scritto:
Hi all
I have written an article about the recommended PCB Rev 2 modification that prevents potential destruction of IC402 (74CBT3253 BPF MUX) due to large parasitic oscillations. See?
This modification involves adding a small signal diode (such as 1N4148 but it is non-critical) to the Tx/Rx switch transistor Q508. It is highly recommended for any QMX Rev 2 owner whose kit or assembled radio was shipped during 2023.?
Very important to note: - This modification is NOT required for any QMX Rev 1 PCB... though if you don't read this note and you do it anyway, there will be no harm done.?
- This modification is NOT required for any QMX Rev 2 PCB shipped in 2024, the QRP Labs team are already modifying all PCBs (kit and assembled radios) before shipment.?
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Minor edit to the description on the web page is needed:
Currently: "TRANSMIT:?During receive, the "RX: signal is at DC Ground potential, as is the Q508 source"
This needs to say "during transmit" (looks like a copy & paste error).
73, Dav
Hi all
I have written an article about the recommended PCB Rev 2 modification that prevents potential destruction of IC402 (74CBT3253 BPF MUX) due to large parasitic oscillations. See?
This modification involves adding a small signal diode (such as 1N4148 but it is non-critical) to the Tx/Rx switch transistor Q508. It is highly recommended for any QMX Rev 2 owner whose kit or assembled radio was shipped during 2023.?
Very important to note: - This modification is NOT required for any QMX Rev 1 PCB... though if you don't read this note and you do it anyway, there will be no harm done.?
- This modification is NOT required for any QMX Rev 2 PCB shipped in 2024, the QRP Labs team are already modifying all PCBs (kit and assembled radios) before shipment.?
|
toggle quoted message
Show quoted text
Minor edit to the description on the web page is needed:
Currently: "TRANSMIT:?During receive, the "RX: signal is at DC Ground potential, as is the Q508 source"
This needs to say "during transmit" (looks like a copy & paste error).
73, Dav
Hi all
I have written an article about the recommended PCB Rev 2 modification that prevents potential destruction of IC402 (74CBT3253 BPF MUX) due to large parasitic oscillations. See?
This modification involves adding a small signal diode (such as 1N4148 but it is non-critical) to the Tx/Rx switch transistor Q508. It is highly recommended for any QMX Rev 2 owner whose kit or assembled radio was shipped during 2023.?
Very important to note: - This modification is NOT required for any QMX Rev 1 PCB... though if you don't read this note and you do it anyway, there will be no harm done.?
- This modification is NOT required for any QMX Rev 2 PCB shipped in 2024, the QRP Labs team are already modifying all PCBs (kit and assembled radios) before shipment.?
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Tnx Hans, will do the mod ASAP.
A quick question: would there be any reason for which a Schottky diode wouldn't work (even better) in this scenario? I honestly can't see one and I have a whole bunch of them, so I'm tempted :-))
73s
YO3GFH
op. Adrian
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Hi Adrian
I don't know of any reason?why not Schottky. I haven't tested it. Any other views on this??
Tnx Hans, will do the mod ASAP.
A quick question: would there be any reason for which a Schottky diode wouldn't work (even better) in this scenario? I honestly can't see one and I have a whole bunch of them, so I'm tempted :-))
73s
YO3GFH
op. Adrian
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Adrian, What part are you thinking of using?
A 1N5711 for example will not be able to handle the current peaks, but it has a nice low capacitance. A rectifier for a power supply could handle the current but would present a much higher capacitance. The devil is in the details...
JZ
Hi Adrian
I don't know of any reason?why not Schottky. I haven't tested it. Any other views on this??
Tnx Hans, will do the mod ASAP.
A quick question: would there be any reason for which a Schottky diode wouldn't work (even better) in this scenario? I honestly can't see one and I have a whole bunch of them, so I'm tempted :-))
73s
YO3GFH
op. Adrian
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Schottky diode has lower drop out voltage but also lower max reverse voltage. So it all depends on what is needed.
HNY
--
73 Bojan S53DZ
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Thanks for the great write-up, Hans and John!
These seem to be about a dime a piece or $4 for 100 at digikey:?
It's the $7 shipping that will get you. I wonder if these would pass intact through the US mail in a standard #10 envelope with letter postage? Has anyone shipped SMD's like this??I'd be willing to buy 100 and ship them out in SASE's in batches of 5 for free if there was interest. (I don't need 100 SMD 1N4148's myself!)
Todd W2TEF
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Hans:
At this time are you recommending the mod for 20m-10m QDX?
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Thanks for identifying the problem and correction.?
I have some 1N4148 through hole diodes - I've done some dry runs of the fix, and find that keeping the diode in place is an issue for me. Is there a recommended way to immobilize the component during this operation?
Thanks,
John KI3J
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Adrian,
What part are you thinking of using?
?
A 1N5711 for example will not be able to handle the current peaks, but it has a nice low capacitance. A rectifier for a power supply could handle the current but would present a much higher capacitance. The devil is in the details...
?
JZ
Hi John, Just got home and checked, they are BAT85S, so I suspect they're no good, since, at a quick glance, this model seem to have a reverse voltage of just 30V. Aaand 10pf of capacitance :-) Will scavenge a 1N4148 then :-) 73, YO3GFH op. Adrian
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73 All,
I've seen SOJ-style SMT devices mailed safely when inside a folded piece of cardstock (like the?QSL card you put the wrong zulu time on).? If it's an ESD-susceptible?device, a wrapping of aluminum?foil or a snippet of anti-static bag inside the card will work.? Some scotch tape is your friend. ?
I don't know how thick an envelope will safely?transit?the US post, but I've heard of envelopes?of QSL cards getting shredded, even though they're thinner than the 1/4" max that the PO requires.? I think it's the thickness change at the bottom of the envelope that causes the mail mutilation with stacks of QSL cards.
73 Jim N6OTQ
On Thu, Jan 4, 2024 at 7:58?AM Todd W2TEF < w2tef@...> wrote: Thanks for the great write-up, Hans and John!
These seem to be about a dime a piece or $4 for 100 at digikey:?
It's the $7 shipping that will get you. I wonder if these would pass intact through the US mail in a standard #10 envelope with letter postage? Has anyone shipped SMD's like this??I'd be willing to buy 100 and ship them out in SASE's in batches of 5 for free if there was interest. (I don't need 100 SMD 1N4148's myself!)
Todd W2TEF
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Hi Adrian
The diode sees only 3.3V reverse voltage. So I'm not sure why a 30V diode could possibly be a problem. Though I can't speak for the rest of its characteristics.?
73 Hans G0UPL
Adrian,
What part are you thinking of using?
?
A 1N5711 for example will not be able to handle the current peaks, but it has a nice low capacitance. A rectifier for a power supply could handle the current but would present a much higher capacitance. The devil is in the details...
?
JZ
Hi John,
Just got home and checked, they are BAT85S, so I suspect they're no good, since, at a quick glance, this model seem to have a reverse voltage of just 30V. Aaand 10pf of capacitance :-)
Will scavenge a 1N4148 then :-)
73,
YO3GFH
op. Adrian
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Hi John
I keep on hand some of what we call in England "Blu tack" but I'm not sure if this name is internationally portable. It's a? pliable and mildly sticky putty. When hot it gets horribly sticky so it takes 1) some practice and/or thought to stick it in an appropriate place so you can remove it afterwards; and 2) some patience to wait a few moments for it to cool down before you remove it after soldering the little SMD.?
73 Hans G0UPL
On Thu, Jan 4, 2024, 6:31?PM john.christopher2 via <john.christopher2= [email protected]> wrote:
Thanks for identifying the problem and correction.?
I have some 1N4148 through hole diodes - I've done some dry runs of the fix, and find that keeping the diode in place is an issue for me. Is there a recommended way to immobilize the component during this operation?
Thanks,
John KI3J
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Hi Chris
At this time I'm recommending this diode fix for 20-10m too. But I'd love to get more community feedback on this. Since personally I haven't seen the fried MUX issue on any Rev 2 board (post C509/R510 change). So I'm at the mercy of feedback from people who have had the issue and are sure that this issue really is the cause of their particular problem.?
I personally doubt there is any problem with 20-10m because I didn't see any large parasitic oscillations on these bands even before the C509/R510 changes. So I don't *think* it's needed on 20-10m but prudence would dictate recommending it on ALL QMX, after all I have been wrong before, and indeed recently, several times :-/
73 Hans G0UPL
Hans:
At this time are you recommending the mod for 20m-10m QDX?
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Hi Jim,
If you¡¯re considering using SOD323 format diode (size to span FET directly) it¡¯s only 1.1mm or 0.04¡± thick from the info I found for the ones I ordered. So shouldn¡¯t be an issue to post in normal letter.
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If purchasing 1N4148 diodes, also consider the 1N4448 alternative with a lower junction capacitance to have a quantity on-hand for applications where the lower C is beneficial.? For NA customers, Mouser has the 1N4448 in a SOD3232 package for $0.10 ea. in >10 quantity. ?Price per piece is less than the comparable 1N4148.? There¡¯s no performance benefit in the QMX mod over the 1N4148 but if placing a new order, at least consider the 1N4448. ?
? Paul, W9AC ?
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From: [email protected] < [email protected]> On Behalf Of Rowan G0KLH via groups.io Sent: Thursday, January 4, 2024 12:18 PM To: [email protected]Subject: Re: [QRPLabs] #qmx PCB Rev 2 recommended modification ? Hi Jim,
If you¡¯re considering using SOD323 format diode (size to span FET directly) it¡¯s only 1.1mm or 0.04¡± thick from the info I found for the ones I ordered. So shouldn¡¯t be an issue to post in normal letter.
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If you send me an SASE I'll send you some 1N4148 / 1N914 diodes.? I have about a million of them (well actually a thousand). Include a folded piece of cardstock with 1N4148 written?on it so I'll know what the SASE is for.
My QRZ address is good.
73 Jim N6OTQ
On Thu, Jan 4, 2024 at 11:52?AM Paul Christensen < w9ac@...> wrote: If purchasing 1N4148 diodes, also consider the 1N4448 alternative with a lower junction capacitance to have a quantity on-hand for applications where the lower C is beneficial.? For NA customers, Mouser has the 1N4448 in a SOD3232 package for $0.10 ea. in >10 quantity.? Price per piece is less than the comparable 1N4148.? There¡¯s no performance benefit in the QMX mod over the 1N4148 but if placing a new order, at least consider the 1N4448. ?
? Paul, W9AC ? ? Hi Jim,
If you¡¯re considering using SOD323 format diode (size to span FET directly) it¡¯s only 1.1mm or 0.04¡± thick from the info I found for the ones I ordered. So shouldn¡¯t be an issue to post in normal letter.
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Dafydd Walters M0WDV
Todd W2TEF
Paul Christensen