by G0DJA » Tue Sep 17, 2019 4:17 pm
I've removed the 'penny' feed and I think that whoever made the feed up miscalculated slightly.
The usual way to calculate the feed point is to measure the diameter (D) in cm and the depth (d), again in cm, of the dish then use the formula
Feed point (f) cm = D x D/16 x d
Since the diameter of the dish is 25cm and its depth is 6cm the focal point should be at 6.51cm (incidentally, this makes the f/D ratio of the dish 0.26 which isn't great but will have to do for now) but the waveguide only reaches to 6cm from the centre of the dish. So, when I unsolder the dodgy end I'll cut back the block behind the big flange and drill and tap a hole for a screw to hold it in place.
Unfortunately, all of the 24GHz beacons are a bit far away unless there is a really good opening, so I'll have to ask to see if one of the people with a lot more power available than I have with this set up can put up a signal for me to look for.
I've removed the 'penny' feed and I think that whoever made the feed up miscalculated slightly.
The usual way to calculate the feed point is to measure the diameter (D) in cm and the depth (d), again in cm, of the dish then use the formula
Feed point (f) cm = D x D/16 x d
Since the diameter of the dish is 25cm and its depth is 6cm the focal point should be at 6.51cm (incidentally, this makes the f/D ratio of the dish 0.26 which isn't great but will have to do for now) but the waveguide only reaches to 6cm from the centre of the dish. So, when I unsolder the dodgy end I'll cut back the block behind the big flange and drill and tap a hole for a screw to hold it in place.
Unfortunately, all of the 24GHz beacons are a bit far away unless there is a really good opening, so I'll have to ask to see if one of the people with a lot more power available than I have with this set up can put up a signal for me to look for.
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