10GHz beacon project
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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 ;-) Thanks, Bob - N3XKB in Los Alamos, NM |
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K Chapman
On 12/22/21 18:01, redarlington wrote:
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 https://www.antenna-theory.com/antennas/aperture/slot.php https://www.researchgate.net/figure/Cylindrical-horn-antenna-with-8-12GHz-11_fig1_324433933 AK5Z |
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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. -Bob On Wed, Dec 22, 2021 at 10:42 AM K Chapman <mailbox@...> wrote:
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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
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Hello all
Very interested in the progress of the 10ghz beacon Do you have a location where you are going to put it?
I am in the progress of getting my 4ft dish up and 30 watts at the antenna /digital ready I live in dm25re Bullhead city az I also go out rover with 30inch dish and 30 watts / digital ready
I have a 10ghz digital group on facebook And you are welcome there
From: main@nmvhf.groups.io [mailto:main@nmvhf.groups.io] On Behalf Of redarlington
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.
-Bob
On Wed, Dec 22, 2021 at 10:42 AM K Chapman <mailbox@...> wrote:
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No location, we're just spitballing at this point, but it's real enough that I thought it worth mentioning here on the list. My roof (or just above up on the tower) is in the shadow of Pajarito, so aiming half the power in that direction using an omni doesn't make an enormous amount of sense. But I'm close with RMHAM and may be able to pull off some magic and get installed up on Pajarito on the tower up there, or maybe at another site at Sandia Peak. Tackling the easiest bits first is where the antenna comes in. That said, I've never had to hold a 0.003" tolerance, but have done much better than that for the fun of it. Camera mounts for an old LANL project out to the limits of my calipers at whatever the temperature of the shop was at the time as an example. The trick will involve doing some test cuts and see where they measure and adjusting from there. With 6' of material, there's plenty to experiment with. I'm also handy with microcontrollers (PIC in particular) and can whip up hardware to control the thing. I'd be interested in stepping the power down between 3 levels and a CW ID, but running a stepped attenuator over months or years will be problematic. No moving parts and adjusting input amplitude early in the RF chain with zero moving parts is probably better. But that's for the future but worth thinking about now, as passively as it might be. I was thinking roughly 2W but I'll see what's out there on the market. This will be a long term year long thing should it gain momentum I think. Input from the group is VERY welcome. I'm new at all of this stuff. As comfortable as I might feel at 23cm, 3cm is a world where I have limited capabilities to do any testing. -Bob On Wed, Dec 22, 2021 at 11:29 AM n6rmj <n6rmj@...> wrote:
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Paul Probert
Bob,
Hi, Paul Probert here. I've been looking for a 10 GHz beacon to help with lining up and testing a 10 GHz station I'm putting together here in ABQ. So I'm glad to hear you are working on one up there in Los Alamos. Maybe we can collaborate. One of my neighbors used to do some work on the commercial antennas up on Sandia Crest and maybe he'd suggest somebody to talk to about getting permission to mount a beacon up there and give us some power to plug into. On the precision of the slots on your omni antenna I'm not sure but in my experience things like that work acceptably well without requiring super high precision. To build an omni one idea is to make some kind of disc-cone antenna. Wouldn't need to be much but a couple copper cones mounted on the end of a piece of .141 inch hard line. It would end up being vertically polarized. At the moment I have a VNA that can be used to check the SWR of any such antennas at X band. Did you have something in mind for your signal source? For my station I've put together a synthesized source based on a YIG oscillator and a Rubidium reference. Waay overkill for a beacon. But I think there are a few synthesizer chips available these days with built in VCO's that might be acceptable. Paul Probert |
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