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Hello Andy, Saturday, December 23, 2017 With my high power Class D amps used with a U3S I have looked into protection quite a lot. Whilst this VHF circuit initially probably looks irrelevant it,

I have a U3S which has started to act strangely. When I feed my beam it behaves well transmitting every 10 minutes as programmed. I also have an end-fed long-wire that is resonant on the Ham

I think you may well be right, so I guess one has think of both monitoring and reacting to high voltage or current. Options. (1) Use a current limiting PSU (2) Use a voltage sensing device to

Can be either but each if from different causes. I read about all of the failed PA devices in the emails and it makes me wonder why design and calibrate the output for perfect conditions (perfect

Andy, I do not think moving up is an option for JA? I'm just the messenger. But if I operated 80m WSPR perhaps I'd be pleased. Or if I operated 80m CW I might not. But as it's a WSPR default I guess

Andy, The way I see it is low output impedance could be high PA current. High output impedance could be high PA voltage. But what I do not know is how much antenna impedance affects the PA devices

Jan, Thanks, interesting that a bigger device is not really suitable for class E QRP. But protection needs many more components. I'm not sure whether I would bother provided just the BS170s

This is very common in high power amps. Across the device, not the antenna and a TVS or “Transzorb” type device not a zener. Just make sure the clamp voltage is calculated right. Dr. William

Aren't both symptomatic of each other ? In which case, choose the easiest parameter to monitor and deal with. 73 de Andy

Why does everyone have to move to accomodate ONE country ? Reminds me of a story I read today that an Aussie beacon on 50Mhz has gone QRT just because someone has arbitarily decided that it's now

This very good Class E tutorial and design information by?Dan Tayloe, N7VE?http://www.norcalqrp.org/files/Class_E_Amplifiers.pdf?have circuits both for over-voltage protection and over-current

Jess, You will not know until you've repaired it:-) But as the devices can be blown by overvoltage or overcurrent I'd think the only way to be safe is to have a SWR bridge with feedback permanently

Putting in a SWR bridge will not keep the PA from blowing, just let you know why it blew.

Keith And also 80m WSPR The default frequency in WSJT-X v1.8.0 is now Dial 3.568600 (TX 3.5600-3.5800) to be within the Japanese allocation. Some are moving... 73 Alan G4ZFQ

What is it that kills the PA overvoltage or overcurrent ? Jan

I like W2EB, Bill's Zener diode idea but was also wondering if a resistor across the antenna terminals would also clamp unwanted voltages. For example, say our load impedance is 50 ohms and we

Great altitudes this morning and nice trajectory.Hoping to grab some spots today !!! Jim,N2NXZ

I've seen other QRP rigs with a 36V or 39V zener diode in parallel with the antenna.? Any experts here see a downside to adding one to at least keep the MOSFETS from going over-voltage? Bill W2EB

Keith, Dial 5.364700MHz (TX 5.366200 +/- 100 in your list format) is within the recently agreed IARU segment and is used for transmitting by European countries that have the IARU allocation. It seems

Well I ordered a 30m kit on the 24th November, number 2264 Being Honest I was not expecting it to arrive until 2018 as I know just how busy they are with orders plus the time of year with xmas