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Here is a simple but effective vswr indicator for use with most qrp radios. I decided to build one to fit inside my qrp atu but also have decided to fit one in my 40m mfj cub. The reason being for fitting one in the cub when out portable is i notice if i have a dipole cut for 40m the vswr can vary quite a lot depending on each location and placement so an indicator fitted is just that, an indication that things are ok.. I'm not sure if i have enough room to fit inside my atu but as my 817's have meters in anyway this isn't a problem so fitting one in the cub would be fine.
components
RV1 -10K This is useful for adjusting the brightness of the LED i put in place of the meter. R1/2/3 50ohm carbon resistors (2w) i used 2 100ohm 2 watt in parrelell giving 50 ohm 4 watt.R4 1K (0.5w), C1/2 10nf , D1 OA91 or similar.meter 1ma FSD SW1 2 pole 3 way switch.
one tip is if building "ugly" style whils making sure it works as i did is to make sure to connect any loads directly to the ant side of the circuit. I made the mistake of connecting different value loads via jump leads which was confusing the issue and the circuit didn't seem to be working as it should. Example, when i had a 50 ohm load connected via jump leads i couldn't get the LED to go out because the load was not 50 ohm after the leads were connected to it. Once i connected the loads directly to the ant side everything worked as it should.
As it turned out i didn't really have enough room to fit this circuit inside my atu as things are tight as they are so i decided to go with fitting one in the cub. Above is the finished circuit installed into the the cub.It could of been made smaller but i used 100 ohm 2 watt resistors in parellel to give me 50 ohm at 4 watts to be a little more flexible as far as power goes.
above is the cub cover with the LED and swtch to switch the circuit in and out of line. I decided while it was open to fit a dial to adjust power settings to enable me to go very low power without opening the case or trying to get a screwdriver through the adjustment hole .i have decided to make another for my atu using high power resistors i have in my box as these are small and flat. this will enable me to keep things really tight and small. The indicator works very well indeed with the LED showing no light anything under around 1.3
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