what frequencies are you aiming for ?
As it's an antenna analyser, I'm aiming for everything from 160M up to 70cm: so that's 1.8MHz right up to 470MHz - which is a pretty broadbanded range!
The for the v1 prototype I'm aiming to use a vcxo
1 covering 2.5 kHz to 200 MHz as the main oscillator - I'm currently investigating oscillators covering an even larger range, or alternatively having a separate circuit for the HF, VHF and UHF bands, each with a dedicated oscillator and bridge. The v1 prototype will give me an idea of the broadband performance of whatever method I choose: if acceptable I'll expand the oscillator range, if not, I'll make a separate analyser for each region
2.
[miscellaneous quotes that I removed for brevity]
A few references on the definition of SWR (or VSWR):
https://www.microwaves101.com/encyclopedias/452-vswr
http://www.antenna-theory.com/definitions/vswr.php
https://en.wikipedia.org/wiki/Standing_wave_ratio
https://www.arrl.org/files/file/Technology/tis/info/pdf/q1106037.pdf
The last one, "Understanding SWR by Example" from ARRL looks like it is from the point of view of a HAM.
Some very useful links there
I came across a few of the links in my travels before - but a good collection there!
I did think that the vk5ajl.com swr page was a little error-prone
I was taking everything there with a pinch of salt: particularly on the details!
(Maybe this article is too heavy on math and light on intuitive understanding. There are tons of other articles out there.) These are coupled transmission lines. Note that it depends on incident and reflected waves canceling out at various points, and it is typically designed to be a quarter wavelength long at the frequency of interest. Consequently not very broad band.
I'm almost certainly going to use a bridge for my analyser project: I might make a couple of cheap-o SWR meters using stripline, just to see how it works out - but for the analyser I don't think they'll meet my needs (based on a cursory glance on various internet articles and your own input, I suspect the bandwidth may be a problem)
I take it if it's not 1/4 wavelength then it's just less efficient in it's pickup and will need more amplification before using the output? Ooft.....! Just occured to me that a quarter-wavelength of 160 meters is 40 meters :O... I'm not going to lie, I kinda want to make a 40-meter long piece of test gear and then try to sell it on ebay... or better still, send it to Dave for a two-minute-teardown
ANYWAY - my original goal was to try and figure out how the microstripline directional coupler was achieving it's directionality xD Mission accomplished! Thanks folks!
I'm sure I'll post up the v1 Antenna Analyser project in the projects section as well - I really need to get in the habit of pictorially documenting my projects more often
3: I even considered a live-stream on youtube at one point, but decided I don't have the gift of the gab required to make "soldering" entertaining for anybody save a very, very niche audience (solderaphiles... which is odd because my spellchecker recognises that word: but google doesn't... weird.)
1 Im currently planning on using the
SI5351A-B04486-GT - with some supporting circuitry to transform, clean up and amplify the waveform. Maybe not the best choice, but it's cheap, moderately easy to implement, and covers almost all the frequencies I'd need it for (the UHF region is obviously lacking, but I can always add that later by changing the oscillator module in the v2 model
2which has the added bonus of giving me three times as many boxes-with-dials-and-knobs on my bench
who doesn't want gauges-and-dials-and-knob-boxes
TM on their bench!?
3I'm surprisingly fastidious in documentation for my projects: schematics, notes, research, operating procedures all stored under a unique serial number and stored in a database/filing cabinet. Actually photographing my work though? I think I done it once or twice to show off something? But I haven't really bothered recently!