maximum safe swr

[reytek79]

Guys, with which maximum swr can we operate between bands safely so that the mosfet does not burn

[dl6sez]

Hello Ladys and guys,

about 1:2 should work normally but not really in ft8, more in ssb or cw.
But one can not determine at what swr level your FETs will be killed because it depends on how your impedance of the antenna is and how long you transmit with the not ideal swr. One swr value has infinite impedances which result in this swr. And a class-E PA is not as stable as a class-AB standard PA.
So if you are unlucky and catch a point of an impedance with your antenna that is more worse than another you will kill the FETs, at another impedance point resulting in the same swr it will work flawlessly.
The best thing to keep your FETs is to use to tune with a resistive bridge tuner at your (tr)uSDX antenna port. This lets the swr not getting worser than 1:2. After match is found you switch from "tune" with resistive bridge to "normal" without the bridge in circuit. Long tuning can also kill or pre damage the FETs.
ZM-4 from
http://www.qrpproject.de/ZM4.html

is such a qrp resistive bridge tuner, but it is not produced any more.
But you can still see and study the circuit with all on the webpage. On the left side is the resistive bridge with LED as swr indicator. Tuning is getting the LED as low lighted as possible.

73 de Chris

[VE3RRD]

Information on other possible add on bridge circuits is found at
http://www.qrpkits.com/swrind_case.html and http://www.qrpkits.com/ezseries.html#ezswr

Another approach is the "polite antenna tuner" which lets you adjust the tuner without transmitting
http://www.nd6t.com/antenna/Polite%20Tuner.htm

[Ohwenzelph]

http://www.nd6t.com/antenna/Impedance%20Mollifier.htm
Put it between rig and tuner, let’s you tune up without risking >2:1, add a bypass switch and you get rid of the added loss once the tuner is set.

[N6YWU]

The QRPGuys Multi-Z tuner is another QRP tuner that includes a resistive bridge that limits maximum SWR (if you remember to flip the switch ! ). It's a kit, and the result is small and lightweight. I've built one, and it works well with my (tr)uSDX. 73, Ron, n6ywu

[reytek79]

Hello Ladys and guys,

about 1:2 should work normally but not really in ft8, more in ssb or cw.
But one can not determine at what swr level your FETs will be killed because it depends on how your impedance of the antenna is and how long you transmit with the not ideal swr. One swr value has infinite impedances which result in this swr. And a class-E PA is not as stable as a class-AB standard PA.
So if you are unlucky and catch a point of an impedance with your antenna that is more worse than another you will kill the FETs, at another impedance point resulting in the same swr it will work flawlessly.
The best thing to keep your FETs is to use to tune with a resistive bridge tuner at your (tr)uSDX antenna port. This lets the swr not getting worser than 1:2. After match is found you switch from "tune" with resistive bridge to "normal" without the bridge in circuit. Long tuning can also kill or pre damage the FETs.
ZM-4 from
http://www.qrpproject.de/ZM4.html

is such a qrp resistive bridge tuner, but it is not produced any more.
But you can still see and study the circuit with all on the webpage. On the left side is the resistive bridge with LED as swr indicator. Tuning is getting the LED as low lighted as possible.

73 de Chris

I thought that tr usdx supported more than 1.2:1 of swr in this topic users talk about up to 1.5 with 13v really?

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