Radiocrafts Rf Transmitter Failures.., A RC1180 AMR RF info and advice....

picture link :
http://i151.photobucket.com/albums/s130/DX...leandanttu2.jpg

what were you figuring for the length of the 1/4 wave antenna ?

Nice clean up on the pic.

Okay 1/4 wave calk shows 82mm and I figured using this path for it..

(Reduced size image)

While for testing Ive been wire mounting the Module and soldering the Wire direct, i'm thinking of simple attaching it to where L2 supposed to be.

Only issue we may have is the wire might interfere with the push button, but we are able to go a little wider on this side...

"Windhoek" is in the Republic of Namibia, and technically I could drive there, but a 2 hour flight is better than the 20 hour drive..

Finally got some feedback on this..

The Oscillation that we getting is actually partially design error (or rather Programming error) If the TXD line on the module is pulled low (because of bad code, etc), The Module see's this as a hex code &00, which is the Config mode command, and the module reply's with ">" prompt. This Fooks up the system completely..

BUT.. All the code fixing I've done prior has fixed this problem, and it hasn't occurred lately..

Once the Antenna problems are sorted, this project can go on to the next level of testing.. plus we assemble a few more and run multiple rad's at the same time...

Finally, I feel like it's getting there...

hmmm ... the idea of kinking the antenna around like that does not thrill me .
there are cases where putting in a 90 degree bend or two is acceptable but it has to be done at the correct points with the correct spacing .

a problem you have is the lack of a good ground plane to work the antenna against .
this means that the theoretical length is just that ... the required length will have to be "cut-n-try" .

it may be easier to attach a "rod" antenna (ie : small diameter brass tubing) to the inside of the case use a short piece of coax to end feed it with .
that skinny uhf flex coax is pretty cheap and easy to work with (think of the stuff used on those external antenna wireless cards for comps) .
to my way of thinking this would be better than the possibility of the wire shifting and causing problems .

what does the case look like and how much room is there ?

The bends will act as increased inductance, while the proximity will act as increased capacitance. Overall, the total path length, along a path like that, will be less than 1/4 wavelength. The board will serve as a sort of groundplane or counterpoise; since the antenna is not centered over it, the radiation pattern will be asymmetric, and there will probably be a bit of a standing wave on the board too (which will tend to make it look like a dipole, which isn't bad -- just make sure all the connecting wires have high-frequency type ferrite beads on them!).

If this board is mounted in a larger chassis, make it out of metal, and make sure the board is supported by metal screws or standoffs (obviously, making sure the antenna has a line-of-sight path away from the chassis!). This will improve the RF footprint of the board, reducing the amount of RF carried by the wires (perhaps removing the need for ferrite beads).

Tim

heh ... i forgot to explain an abbreviation or two :
PPE = *iss Poor Engineering
POS-1 = Piece Of *hit , first class/model

@ tim :

yeah ... directionality is a concern i have .
from what i gathered earlier in the postings the units will be stuffed/placed in(to) varying configurations .
it would help if the original contract specifications concerning distance/performance were known .
i can see the possibility that if enough range is a requirement an external antenna might be needed .

update ?

hmm yes.. Update..

So had a few mails back and forth to the manufacturer, and so far we've brought it down to software failure..

The Failed/Blown modules that received on RF but did not transfer out the UART, actually did not pack up, they just got Memory corruption..

Hooked them up to a USB test/Dev board and used their software to comms with it and managed to reset the memory (all 255 bytes of it), well I had to manually set the locations one for one..

As for the Antenna, our other developer likes the idea of a simple piece of wire attached to the board, (Low cost, easy to debug/ repair, etc) however we will be conducting some range & DB tests in the near future..

Currently running one of the boards on an Accelerated calendar to ensure consistent operations.. (2 min = 1 hour)

So far found several dozen problems in the 'Firmware' code and am working to sort these out now...

good enough ... beat the hell out of the whole thing .
freeze it , boil it ... why , you could even urinate ...
but i shall digress .

the antenna is very cost effective .

did the corruption happen because of bad code or because rf was getting back into *somewhere* ?

Sorry, I stand by my "write off" comment here.

I think they owe YOU for debugging this thing :-\

HEhehe ...

I beat the living out of it, and more..

even pulled two more errors in the code (one an extremely serious problem) ..

For me, the antenna story is still up in the air, but progress is progress...

As for the corruption, it came down to going into the config mode, while 2 way comms was still active. Digging deep into the Modules programming modes to find a better way to set the different options we need..

The NVRam has a limited number of guaranteed writes (1000 only), which in the field could give us ~10 years life, which considering the battery life is estimated to ~9 years, is still OK..

seems the RF side of it was the red herring that had me chasing Ghost's...

I'm known as the king of Logic (even on the coding site I'm a member of).. and Logic is whats needed to debug these monsters...

geek : "I think they owe YOU for debugging this thing"

yeah ... the boss is gonna give him a pine float for his efforts ...
a toothpick in a glass of water .

Yeah something like that...

Arg... months later and much progress but little accomplished..

So spent a goodly amount of time writing the PC based code side of the system, and now it's time for final testing...

However we battling to get any sort of decent full comms range.

RC. Eng response!!)

Indoors (in line of sight) we getting less than 20m .. regardless of antennae used..

So my BIG Question to the HF Antenna GODS, is .. Which style/size of antenna is best for TX and RX ????

Please also note that on one end (the Meter) it is impossible to setup Ideal conditions, but the Board needs redesigning, and we'd like to work out the best performing Antenna on to it...

did you ever notice that the vast majority of "portable transceivers" use a vertical 1/4 wave sticking out of them ?

i believe that figuring out what is going on is to use a short piece of decent coax to couple the tx/rx section to a vertical 1/4 wave cut to frequency (it will be broad in response as the "Q" will be fairly low in the range you are running) .
the output of the rf section has to match the impedance of the coax ...
50 or 52 ohm coax is a good impedance to use/design around as this is a fair match for the impedance of a 1/4 wave antenna (and is almost "universal" with these types of devices) .
run it against a ground plane .
this is a pretty simple setup .

any deviation from straight , working against a ground plane , proper impedance matching , low standing wave (etc .) , will decrease the performance as far as rf receive and transmit goes .

what you have to prove is the basic design (rf section impedance matching and so-forth) is correct .
if the guys said that they were getting reasonable distances in their lab ... you must be able to prove them to be correct .
the way to do this is to eliminate possible errors in your design and equipment .

once you can reproduce the ranges they stated , by implementing good basic rf design work and software de-bugging ... THEN you can start modifying the antenna "hardware" and design .

there are certain things that have to be proven out first ...
among these is the actual impedance of the tx section output .
this includes any and all constructions (ie : "stripline") associated with it .

jumping around willy-nilly and trying things is a crap-shoot at best .
one has to be methodical in the approach in order to get results .

Thanks CBW..

Might just print your reply, and place it on the other Developers desk...

'Here are some of the answers'.... now let me do my thing...

Big Ouch...

Well this project has pretty much been shelved, After me spending almost a year on it.

The Client, who's the company selling these meter to the councils, (we develop and manufacture only) came passed yesturday, and effectivly told us that they can get the same (Rather similar) product at 20% less than our best price per unit.

And all this just when range testing results started getting good (lots of RF noise at the office) 100m line of site at home.

Time to pack it up and move on to the next one.. which will also have a 868 radio of different design (proto has 350m range line of site), however it will also include a IR port and a few other features...

So about 1/2 of the PC software is still usable, but 0 of the firmaware.. (different uC)..

Back to the chalk board now..