Why the mis-matched impedances 72 ohm to 50 ohm coax?
It’s done on purpose to introduce additional loss in the RF chain.
Makes good sense to me. Just unusual. Is the DreamCatcher’s input actually a 72-ohm device?
I’m not sure I understand the question, but as more information:
The LNB is outputting 75-ohms–no way around that.
The Dreamcatcher is expecting 50-ohms, but the losses from the mismatch are not huge.
From the u.fl/IPEC connector backwards (on the board), everything is 50-ohms.
I appreciate your time and explanation. The question arises from my having worked with transmitters a good deal of my professional life, and the importance of impedance matching. As we are working with just a receiver in this application, I understand the answer provided. Thanks!
Here is what is not apparent from the pictures.
- The LNB can be twisted/skew-adjusted and stay in place
- Both of the holes next to the LNB are water tight
- The LNB can be removed and the hole is closed with a plug
- The F-connector allows for optional remote placement of the LNB
- A cover will be placed on top of the Dreamcatcher
- The bottom allows a stand to be attached for elevation adjustment
- There may be foam on top of the Dreamcatcher to hold a battery in place
My only concern is heat, midday in summer. It’s a shame it’s too big for a http://openh.io/rubicon/ You could then have bonded the cpu to the aluminum.
What purpose does the inner case serve? I’d be temped to leave it out so at least you have airflow inside the case and the slightly larger surface area for heat transfer.
Assume you’ll put some desiccant sachet in?
The clear plastic above the PCB allows items to be stored on top of it. If we are seeing heat as an issue, a sink plate can be affixed to the bottom of it.
A dessicant could be added. The boards will be conformally coated.
How about a wedge? It could be RF transparent to the LNB and push under the box (maybe on a rail?) thus elevating the box up to say, 50 degrees? It could be stored inside the box when not in use. Put the whole lot on a table or shelf or whatever. Perhaps the battery pack could also be stored inside?
@Mark_Phillips The problem with a wedge is that it doesn’t allow for any change in elevation. Depending on where the user is, the angle can be substantially different. What we have in the next version are pairs of holes under the enclosure which allow a bent metal U to be placed in them. This acts as a cheap, light adjustable stand.
Yes it does. You put more or less of the wedge under the box. That’s why it has to be RF transparent otherwise it’ll be in the line-of-sight for the LNB at low elevations.
The U-shaped stand is a good idea.
Ah, it’s movable. Yes, that makes sense.
That case looks good! Is this (DC3 + that case) likely what is going to ship to your patient IndieGogo backers? Thanks.
Yes, for any of the backers that want this version, we will be happy to ship it. We have a much smaller, thinner version in the works, but it’s a very slow development process.
For DIY’ers or those with high shipping by weight a 20L food bucket and lid, even a small 5L bucket would fit.
Maybe call the option a DIY cover kit with rubber glands for the punch/drill holes is a better idea or at least an option for the target demographic? Just an example. Available new and used almost everywhere and might also provide nice anti-theft camouflage. Outernet logistics could also make an external from-China order to get a bucket on the way as part of their hardware order?
Most are PET https://en.wikipedia.org/wiki/Polyethylene_terephthalate plastic
I doubt it would attenuate the signal much or have enough velocity factor off-tune or lensing for our purposes though I am not well versed at microwave freqs.
Ideally pick one with IR reflective UV resistant surface, radio-transparent at our Ku band and L band wifi, maybe logo but consider neutral for camoflauge, glands and passthrough cables for power and possibly the LNB cable for external antenna install, a few CM of that radio antenna connector sealing tape goop for the power if it has to go up onto a roof.
It might be good to have a list of approved 2A chargers as I have found most non-OEM chargers either lie about the true rating or are way over-driving way past ratings of the components and fail early sometimes catastrophically.
The production version will not be black.
There will also be covers for the holes.
Everything feels really solid, though a little heavy. The pre-production version will be ready after Chinese New Year (February 3rd our so). The main seal needs to be adjusted and the metal stand needs shortening.
Just reviewing the picture…
- How would the elevation be “fixed” to the desired angle ?
- Add an opening to mount a cooling fan … maybe on opposite side from lnb opening
maybe 80mm x 25mm at xxx.? voltage?
or 40 mm version to limit power requirements