Re: 10GHz beacon project

James Duffey

A good rule of thumb when deciding tolerances of all kinds involving lengths of things in RF applications is the one degree rule. That is, a tolerance resulting in one degree of error is acceptable. There are 360° degrees per wavelength, so the tolerance is easy to figure out. For 10 GHz, or 3cm wavelength, that error is 3cm/360° = 1/120cm = 0.003 inches. That exceeds my matching capabilities, but you can probably do that with care. A looser rule of thumb is that tolerances should be held to 1/100 wavelength, which is about 0.010 inches. You should be able to do somewhere in-between, which I would guess is fine. Someone with a microwave modeling program like PUFF can verify this, but I no longer have access to those tools.  - Duffey KK6MC 

On Dec 22, 2021, at 11:54, redarlington <rdarlington@...> wrote:

I did get my needed info about the slots needing to line up "front to back", and was recommended to add wings for a better pattern.   We very much do want an omni and have various horn and choke ring feeds.   Smooshed flat round pattern is what we're after.   Maybe anyway, depending on a few things.  Thank you for the additional info.  I have a lot of homework to do before I cut any metal.


On Wed, Dec 22, 2021 at 10:42 AM K Chapman <mailbox@...> wrote:
On 12/22/21 18:01, redarlington wrote:
Hi all,

I managed to find a 6' stick of WR90 with a choke flange at each end.  My plan is to work with a friend in Albuquerque to build a pair of slot antennas using W1GHZ's documentation and spreadsheet, and split the rest of the waveguide up between us.  

In just about every picture or video of these things, I see the slots go straight through from one side of the WR90 and out the other side, like they were done with a wire EDM machine (even when done on a mill).   My original plan was to mill one side, and flip the part and then do the other, which would leave me with slots that do not line up front to back.  My question is, does this matter?   Have CNC, can adapt, and all that.  But if the vertical slots are effectively horizontal dipoles, why would it matter if they were lined up with each other or not?

I'm more of a machinist than a microwave plumber, but I'm not much of a machinist ;-)

Bob - N3XKB in Los Alamos, NM

Yeah I just want to chime in here. I think you’ll want some gain at that frequency (slot antennas are roughly omnidirectional). If you have tooling it would be just as well to make a horn antenna or even a backfire antenna


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