Kiwi's XPS test results are up.

[JimDrew]

Julez, "spherical" is our term. Digi calls it omni-directional, or as their lead engineer put it "a ball with north and south dimples". Digi's antenna patents pertain to their sensitivity and selectivity using their antenna.

[Julez]

Of course they are omni-directional in one plane.

But have a look:
http://ftp1.digi.com/support/documen...90000976_D.pdf

There are "omni-directonal" antennas listed with up to 15db. This clearly means, that they cannot be omni-directional in all 3 dimensions, and Digi has another understanding of the term "omni-directional" than what you want us to believe that their antennas are.
Remember, Xbee modules were designed for industrial applications, where the 3rd dimension is hardly needed. There is no point in sending data to the factory floor or ceiling. So the radiation patterns in the datasheets only represent the horizontal plane, not the vertical one.
Obviously, you do not know how to read such diagrams, and concluded that the radiation strenght is equal in all directions, and invented the term "spherical radiation".
There is no other explanation possible.

Thus, until a patent number concerning the antenna is presented, I do not believe a word.

[tadawson]

Note though, that on page 139 of the document that you reference, the on-board monopole ("wire") antenna is shown to have a gain of only 1.5dBi which would indicate that it's deviation from a true sphere will be very minimal . . . as Jim said "dimples on the top and bottom" . . . pretty well sums it up . . .

- Tim

[Julez]

This is just what I said: It is just a normal monopole, nothing patent-worthy, let alone patented.
Therefore I still doubt there is a patent regarding the antenna.

[tadawson]

I guess I could care less about the patent status myself . . . and frankly, even if it is a monopole, that does not in any way prevent Digi from patenting their application, or perhaps the overall module, including the antenna.

My point was more to the fact that 1.5db gain over isotropic is pretty damned spherical, patent or not . . . .

- Tim

[Four Stroker]

This battle has been raging for years. Many consumer wireless devices have spherical antenna patterns - deliberately - if you allow 20 dB dimples in your sphere. The Digi module antenna is a piece of wire soldered onto a rather small ground plane. Of course, you have to allow for a 20 dB drop due to orientation in your link budget. There is no magic to be found here anywhere as Julez has indicated.

Let's see, 1.5 dB gain and 20 dB dimples. So in a bad place, a net gain of negative 18.5 dB. I would expect an anisotropic antenna to have a constant 0 dB gain. That you could patent.

[JimDrew]

Several years ago when this was a big discussion, someone actually tested our system in one of Boeing's anechoic chambers. The radiation pattern was found to be "earth shaped with minor polar dips". In a controlled experiment, the absolute worst case we could come up with having both antenna tips pointed at each other was a 7dB loss, which is just under 1/2 the range of normal.

[Woketman]

Yeah I recall the Boeing test. But I also recall that the details were VERY illusive and no hard data was EVER shown. there were excuses made about "well, the guy can't show the data cause he was doin' it on the side".

Yeah, right. Jim, with your reputation for being (as someone said recently in another post) "economical with the truth", I don't see why ANYONE would even consider that as ANY sort of evidence. Let's see hard data, and don't go quoting Maxstream specs and stuff. Let's see the Boeing data, once and for all.

Poop or get off the pot!!!

[Charley38]

	Quote: Originally Posted by RocketFuel
	OK sweatpea, got the message. Fact is I purchased an XPS JR module + 2 x 8 chnl receivers for my 9XII some time ago and sold them soon after (unused) on ebay because of information on these forums. I am now about to try again, and the new XPS V3 seems to read OK. I don't want a pat on the back and do not follow the pack. All I need is true information about the current state of 2.4 ......

One thing I'm curious about: Why do you want to try XPS again?

As to the current state of 2.4 GHz systems, Futaba & Spectrum are not the only alternatives. Airtronics and Hitec are selling frequency hopping SS 2.4 GHz radio systems too. I have both, since I favor the frequency hopping approach.

CR

[Four Stroker]

http://ftp1.digi.com/support/images/...eeAntennas.pdf

And of course you multiply the dimple by 2 for transmit and receive worst orientation.

[Woketman]

So where is the Boeing data Jim???

I'm holding my breath....... hurry........

[JimDrew]

Keep holding your breath! I have never seen the Boeing data. When accusations were flying that tax payer money had been used to prove/disprove the radiation pattern, the whole thing was suddenly hush-hush.

Our additional ground plane and antenna tuning traces significantly improves the polar dimples.

[Woketman]

How amazingly convenient!!!

The Boeing data is most likely imaginary anyway. But I think we all knew that already....

[Cherokee Jim]

Hello All,

The following text is larger than normal so it will be easier to read!
Font is Comic Sans for the same reason.

Here is another bit of info and test results from Digi for the XBeePro 900MHz.

Of course this does not apply to 2.4GHz But the test method is interesting, similar to their test method for 2.4GHz.

I am a firm believer in the more information the better.

I did my own test on the early XPS and Spectrum systems and there was no difference in ground range.

I concluded that I liked the XPS System better because I didn't like the connectors used for the add on receivers and I didn't like the the idea of feeling like I had to add on a bunch of receivers to get the job done.

Since that time Jim has changed his frequency Hopping technique, all radio systems are allowed to evolve - yes I am a firm believer in Evolution!

Since that Time I have moved on to Weatronic and ACT with great results and No Problems.

Having Said that the Airtronics/Sanwa 2.4GHz seems to be doing very well and at a great price. They have one feature that I have always wanted, differential expo - e.g., the expo values for up elevator and down elevator can be set differently, after all the control response for most aircraft is not equal for opposite control inputs so expo, end points, dual rate, and even servo speed should be independently adjustable for each direction.

Now for the Digi test Link:

http://www.digi.com/pdf/wp_xbeepro868range.pdf

After seeing this one might ask why are we using 2.4GHz !

Hey Jim How is your 900 MHz System coming along?

We should spend more time finding information on these systems and developing test methods. These systems are Packet Radio Systems, we need more than just an oscilloscope to see the PPM pulses, we need software to decode the Packets of information and we need information on the packet protocol and format. The manufacturers don't want to give this out of course. Kind of like PCM, no one wanted to give away their system techniques.

I would suggest that all radio Manufacturers have software that would be used for test purposes as Digi has done in their test.

Such as:

The same 99% received correctly rate.
The test rerun for each Hop frequency.
The results graphed for comparison.

And since this is for test purpose of the RF Data Link the manufacturer would not be giving away their system.

Weatronic already has this kind of software! ACT has similar software. XPS has some software but it has been awhile since I have used it - Hey Jim what does your software do these days? Any chance of doing a set of test software as above?



Happy Flying,
Cherokee Jim Mahoney

[Cherokee Jim]

Hello Again All,

A little add on for my previous post:

While I have my favorite radio systems I don't want any radio system to be found as unreliable - an unreliable system could cause a serious problem and that would be bad for our Hobby and the Manufacturers involved in this Hobby.

I also don't just Wish for my favorite radio to be the best - I want them to really work at being the best, That means the other Radio Manufacturer's must also work hard to improve their systems to keep my favorite system's manufacturer working even harder to stay ahead.

Happy Flying,
Cherokee Jim Mahoney