waveguide / wavelength.. and other stuff

remyxlplyk · 08-14-2002

Meebe someone more advanced than I can answer a few questions...
i was measuring some Ku band downlink rectangular waveguide and got these numbers:
length = 2/3 L (wavelength)
width = 1/3 L
probe = 1/6 L , 1/5 L from the back.

Now, assuming that my measurements were good enough:

the length vs width of the waveguide is.. odd. thirds are pretty much unheard of in RF... Am i right in thinking that's to match the impedance, and if so, doesn't that mean the circular waveguides (cantenna) will radiate, but be grossly mismatched?

in making a cantenna/ waveguide, do we want an actual 1 L diameter tube, 5/8th L, 1/2L, or what?

could some people measure their cans (heh) and post the diameter in milimeters, please?

two more questions!

where should the probe REALLY be (and how long!), in relation to
wavelength?

and finally..
the jacks on the orinoco cards.. are they SMB or SSMB????

thanks!!
rmyx

rogerRabbit · 08-14-2002

I've just put my cantenna statistics up; the links I mention are the ones that helped me to get going at these frequencies & usefully cover the ground you're looking at.

BTW, I've always thought (assumed, perhaps) that the cantenna's impedance is much more (only?) a function of the length of the driven element.

remyxlplyk · 08-14-2002

cool. thanks for putting that up!
figgured out thusly that diameter is 3/4 L, 1/4 L long probe, set 3/8 L from the back.. now 3/8th's still doesn't make a lot of sense.

i wonder anyone's tried using 2 1.5/8th L probe elements set at 90' to each other, or if that'd just introduce more noise, phase problems and multipath crap rather than improving polarity reception issues.. i mean sure, the waveguide is circular pol, but wouldn't the probe also need to be likewise?

cheers!
remyxl

rogerRabbit · 08-15-2002

Quote:

. . . 1.5/8th . . .

Just to check, that's 0.1875 and not 1.625?

Quote:

i wonder anyone's tried using 2 1.5/8th L probe elements set at 90' to each other, or if that'd just introduce more noise, phase problems and multipath crap rather than improving polarity reception issues.. i mean sure, the waveguide is circular pol, but wouldn't the probe also need to be likewise?

Do you know of any analogies at other frequencies? It sounds a bit 'unclean' but there's only one way to find out for sure. Are you going to volunteer

?

zorg · 08-15-2002

Quote:

Originally posted by remyxlplyk
i wonder anyone's tried using 2 1.5/8th L probe elements set at 90' to each other, or if that'd just introduce more noise, phase problems and multipath crap rather than improving polarity reception issues.. i mean sure, the waveguide is circular pol, but wouldn't the probe also need to be likewise?

cheers!
remyxl

if you want another probe @ 90deg offset you need to put it 1/2 waveguide lambda instead of 1/4. then you can use both of them simultaneously (but with different xmit/recvr).

btw, it's not circularly polarized. you an easily prove it by rotating the can along its axis and watching the gain change.

08-14-2002	#1 (permalink)
remyxlplyk Registered Member Join Date: Aug 2002 Location: denver, co Posts: 2	waveguide / wavelength.. and other stuff Meebe someone more advanced than I can answer a few questions... i was measuring some Ku band downlink rectangular waveguide and got these numbers: length = 2/3 L (wavelength) width = 1/3 L probe = 1/6 L , 1/5 L from the back. Now, assuming that my measurements were good enough: the length vs width of the waveguide is.. odd. thirds are pretty much unheard of in RF... Am i right in thinking that's to match the impedance, and if so, doesn't that mean the circular waveguides (cantenna) will radiate, but be grossly mismatched? in making a cantenna/ waveguide, do we want an actual 1 L diameter tube, 5/8th L, 1/2L, or what? could some people measure their cans (heh) and post the diameter in milimeters, please? two more questions! where should the probe REALLY be (and how long!), in relation to wavelength? and finally.. the jacks on the orinoco cards.. are they SMB or SSMB???? thanks!! rmyx

08-14-2002	#2 (permalink)
rogerRabbit Peripatetic Stumbler Join Date: Jun 2002 Location: Motueka Posts: 219	I've just put my cantenna statistics up; the links I mention are the ones that helped me to get going at these frequencies & usefully cover the ground you're looking at. BTW, I've always thought (assumed, perhaps) that the cantenna's impedance is much more (only?) a function of the length of the driven element. Last edited by rogerRabbit : 08-14-2002 at 03:49 PM.

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08-14-2002	#3 (permalink)
remyxlplyk Registered Member Join Date: Aug 2002 Location: denver, co Posts: 2	cool. thanks for putting that up! figgured out thusly that diameter is 3/4 L, 1/4 L long probe, set 3/8 L from the back.. now 3/8th's still doesn't make a lot of sense. i wonder anyone's tried using 2 1.5/8th L probe elements set at 90' to each other, or if that'd just introduce more noise, phase problems and multipath crap rather than improving polarity reception issues.. i mean sure, the waveguide is circular pol, but wouldn't the probe also need to be likewise? cheers! remyxl