Hi
I asked a couple of questions about making antennas for 5.8gHz in this thread:
https://www.eevblog.com/forum/beginners/any-rf-antenna-design-boffins-around/.
I got some useful info from that. Now, I've bought myself a directional coupler, which happened to come with a 'negative detector'. This is the coupler:
And this is the detector:
The data sheet for the coupler is here:
http://krytar.com/pdf/2618.pdf. The headline figures are -16dB coupling, directivity > 15dB. I've got a handle on what those two mean from watching W2AEW's videos on couplers. A metric I don't understand is 'Maximum VSWR: 1.35'; what is the implication for that, for trying to measure the SWR of an antenna? I have no idea whether these specifications are suitable for what I'm trying to do, but it wasn't hugely expensive s feel free to tell me!
Assuming I haven't bought the wrong thing entirely, here's what I think I'm going to do - stop me when I go wrong. I think the negative detector is a damn fast diode. I can't find a data sheet - perhaps it's too simple to need one? If I get an SMC connector (for the output of the negative detector), and solder a resistor//capacitor from output to ground, I can measure the (negative) peaks of the rectified signal. By measuring this voltage with the coupler connected one way round, and then swapping it end-for-end and measuring again, I can get figures for forward and reverse voltage and hence calculate SWR. Sound plausible? How does the 'Maximum VSWR' figure affect this, I wonder? I don't *think* I need to worry about coupling, directivity, insertion loss and that stuff, because I'm only interested in the ratio between the two numbers, rather than absolute figures.
Feel free to pile in if you can shed light on any of the above. Incidentally, I flew with a skew planar antenna (four 'lobes' arranged in a circle) of my manufacture on my receiver, in a brief lull in the howling gales - the reception was absolutely rock solid, out to what must be nearly 1000 metres. Beginners luck, perhaps!
Thanks
John