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I am on the road right now, currently in a hotel in Tehachapi. Last night I set up my truSDX connected to a small MFJ16010 tuner, then tossed a wire out into a tree from my balcony, and dropped counterpoise down to the ground. ?I plugged in a cheap straight key and a cheap pair of headphones, called CQ for about 2 min and?had a very nice CW qso with a guy in Sacramento. ??
The whole kit fits in my purse but I actually keep it in a small hand tool bag. ? this was a super proof of concept. The whole thing can come on the plane.
Thanks again to you all and the QRPops group for all of the information and encouragement!
Connie W6EFI -- Connie KN2EFI
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Connie,? I? strongly encourage you to install a 1N4756A diode between rf and ground.? It will? protect your finals.
Doug
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Thanks for the tip¨C ¨C I will look into this once I get back home. I'm glad I have a radio I feel ?comfortable just opening and modifying.
73, Connie W6EFI
On Sun, Jun 9, 2024 at 07:57, Doug Hendricks < ki6ds1@...> wrote: Connie,? I? strongly encourage you to install a 1N4756A diode between rf and ground.? It will? protect your finals.
Doug
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Connie KN2EFI
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I blew the BS170 final transistors (set of 3) twice due to inadvertent high SWR and had to replace them. ?Fortunately, the replacements transistors are inexpensive.
Doug, when you say place 1n47576 between rf and ground, you mean rf antenna output to the ground?
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On Jun 9, 2024, at 08:51, Connie W6EFI via groups.io <stillinger@...> wrote:
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Thanks for the tip¨C ¨C I will look into this once I get back home. I'm glad I have a radio I feel ?comfortable just opening and modifying.
73, Connie W6EFI
On Sun, Jun 9, 2024 at 07:57, Doug Hendricks < ki6ds1@...> wrote: Connie,? I? strongly encourage you to install a 1N4756A diode between rf and ground.? It will? protect your finals.
Doug
-- Connie KN2EFI
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Connie and Hiroki,? it's a simple fix.? Just be sure to pay attention to diode band orientation.?
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good advice. Any chance you could resend one of those pictures with the component circled? ? that'll make it a little easier when I get home and dig through my 10,000 emails. If not, it's easy enough to figure out.
thanks again, Connie W6EFI
On Sun, Jun 9, 2024 at 14:18, Doug Hendricks < ki6ds1@...> wrote: Connie and Hiroki,? it's a simple fix.? Just be sure to pay attention to diode band orientation.?
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Connie KN2EFI
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It's the diode connected to the black connector at the top middle of the picture.? ?Do you see it now
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How does the diode protect against high SWR? What is the theory?
Hiroki AH6CY by
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On Jun 9, 2024, at 14:57, Doug Hendricks <ki6ds1@...> wrote:
?It's the diode connected to the black connector at the top middle of the picture.? ?Do you see it now
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Keeps the SD junction? voltage below 60v limit.? Diode conducts at 47v
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On another topic how do you charge the internal battery?? What size plug, what is polarity?
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Doug, I assume you are talking about the USDX radio¡¯s battery. The (tr)uSDX has no internal battery. A charger came with my USDX. Since it is charging 11 V battery, ?I assume it is feeding 11-12V. I never measured it so it is just a guess. I will test it when I get home (I¡¯m in Seattle now). The plug is smaller than the external 12-13.8V ?ps plug which is a common size.
Hiroki AH6CY ?
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On Jun 9, 2024, at 16:12, Doug Hendricks <ki6ds1@...> wrote:
?On another topic how do you charge the internal battery?? What size plug, what is polarity?
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I discussed with Ed Fong (WB6IQN)? concerns about installing an internal battery on these radios. You don't want the biggest Li+ pouch cell that will fit.? ? They expand 10-12% radially as they age.? ? You don't want to puncture a puffy battery.
73 de AI6KG
Doug, I assume you are talking about the USDX radio¡¯s battery. The (tr)uSDX has no internal battery. A charger came with my USDX. Since it is charging 11 V battery, ?I assume it is feeding 11-12V. I never measured it so it is just a guess. I will test it when I get home (I¡¯m in Seattle now). The plug is smaller than the external 12-13.8V ?ps plug which is a common size.
Hiroki AH6CY ?
On Jun 9, 2024, at 16:12, Doug Hendricks <ki6ds1@...> wrote:
?On another topic how do you charge the internal battery?? What size plug, what is polarity?
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In theory, an FET subjected to an overvoltage condition goes into Avalanche Mode Breakdown, which is a region where the?FET functions like a zener, with a wattage rating equal to the FET wattage rating. That zener might be one-watt rated, maximum. I'm guessing it would blow out faster than the FET.
How does the diode protect against high SWR? What is the theory?
Hiroki AH6CY by
On Jun 9, 2024, at 14:57, Doug Hendricks <ki6ds1@...> wrote:
?It's the diode connected to the black connector at the top middle of the picture.? ?Do you see it now
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I prefer units, such as the (tr)uSDX, which does not have a built-in battery. ?That allows me to plug in batteries of varying voltages to safely check the SWR of portable antennas (or operate QRPp at even lower power levels), by using 6 to 8 Volt battery packs (or recycling a 9V one that a smoke detector had discharged to 7V). ?Then I switch to a higher voltage battery pack only if the antenna shows a good SWR.
73, Ron, n6ywu
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My understanding is that a Zener diode "Zeners" in the reverse direction, but acts as a regular silicon diode in the forward direction, i.e., with a nominal 0.7 V forward drop. Since the transmitter output device "sees" AC, is a single shunting Zener diode appropriate? Wouldn't two Zeners back-to-back (i.e., in series with opposing orientations) be better? See, e.g., below.
Best, --David KM6RI
https://resources.pcb.cadence.com/blog/2020-what-happens-when-you-connect-zener-diodes-in-series
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David: you would be correct, if the zener were placed across the RF output. Then it wouldn't work at all. The zener would probably blow right away.
I got the impression this zener was placed in parallel with the FET, to clamp the peak voltage.?
AC voltage can't appear across a FET. FETs have both an Avalanche-Mode breakdown characteristic (resembling an internal power zener), and an intrinsic diode (also resembling a power zener). This internal parasitic diode is antiparallel with the switching part of the device.
My understanding is that a Zener diode "Zeners" in the reverse direction, but acts as a regular silicon diode in the forward direction, i.e., with a nominal 0.7 V forward drop. Since the transmitter output device "sees" AC, is a single shunting Zener diode appropriate? Wouldn't two Zeners back-to-back (i.e., in series with opposing orientations) be better? See, e.g., below.
Best, --David KM6RI
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Cooy and paste from above: "I? strongly encourage you to install a 1N4756A diode between rf and ground."
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Jeff Reagan
David