thUndeadMod v3.4 - openLRS S**T just got real :)

[WSWhitby]

Hi All,
I am about to take the plunge and buy some UHF equipment, Santa will be a little early. I have read most of the posts on this forum back to #1, very interesting it proved to be. If however less than completely self explanatory.
My questions are :-
1.   OpenLRS or if not what? Please suggest!
2.   Why is their a lot of effort going in to 459 MHz rather then sticking with 433 MHz? If its a matter of legality in UK then why are people using it even as a comparison. It seems to me that antenna are available off the shelf for 433 but you need a shorter specially designed antenna for 459 MHz and a lot of questions have been asked about which is the best.
3.   Why is thUndead's Mod 4 fw named final have all the bugs and more importantly the possible add on's been incorporated or is it a shortage of Red Bull and Pringles that have  caused this rather abrupt stop.
4.    Is the system now reasonable robust and can it be used with confidence in MOST rf environments?
5.    Why is Flytron not more active on the Forum as it his hardware that hosts the fw.
6.    Why a lack of activity for the last 8 or so weeks? Bad flying weather I will grant you but not a total grounding.

Hope to get some if not all the answers.

Regards

John
 

[Coyote]

Hiya

1) OpenLRS or EZUHF, Chainlink,Dragonink,Rangelink or the new Hobbyking version of OpenLRS to name a few.

2) Yes its all  down to 459Mhz being the legal UK frequency to use. There is only 1cm difference between a 1/4 wavelength of 433 and 459 so the 433 antennas will work just fine while using 459Mhz.

3) It is named final because thUndead has stopped developing the code after this release. Users have reported it works pretty solidly.

4) Yes the system has been used and works fine, many km flown on it now

5) Fytron tends to leave the clued up members to help others out and progress the system. Its an open source project so apart from technical electronic questions they do not have to answer much but they do answer when it needs it.

6) No idea who`s flying on OpenLRS right now, I think Papa does still 

[WSWhitby]

Hi You Both,
Looks as if its a try with Turkish delight, though I am always tempted by any thing from Hobby King.
Thanks for your replies.

Regards

John

[WSWhitby]

Thanks for that papa, by the way which antenna are you using? and the questions that I probably should not ask What frequency?  ;) Are you using channel hoping? if so how many channels and perhaps the $1000 question any simple precautions I should take.

Thanks for input so far.

Regards

John

[WSWhitby]

Hi Papa,
Yep that covers it. When you say custom dipole on Rx could you give me more details, a bit of a pain me asking all these questions but you seem to be "the man" when it comes to UHF.

Keep up the good work and

Regards

John

[Devonian]

A custom made dipole refers to an antenna that is made specifically for one frequency.
For 459MHz, two 1/4 wave elements are used, fed directly with 50 ohm coaxial cable.
Calculation is simple...
300 divided by the required frequency, divided by four, to get a 1/4 wavelength...

300/459 = 0.6535 (metres) divided by 4 = 0.163 (metres) or 163mm (163 millimetres).

Cut 2 elements at 163mm and attach them to a short length of coax, add a suitable connector for the Rx and there you have it.

http://en.wikipedia.org/wiki/File:A6-3EN.jpg

Nigel.

[WSWhitby]

papa,
Is your custom dipole as suggested by Devonian? If so how do you mount it on your airframe. It seems that the two options to mount vertically are a little less than practical. One with about a foot of antenna above the wing/body with a coaxial feed to the centre and a requirement to secure one end the other with 6 " or so down below and 6 above with the associated problem of landing on the down bit and still rigidity and mountind difficulties. That is of course if you mount the antenna vertical, which I seem to remember form posts earlier in this forum, that mounting orientation is required.
After doing some more online research I also came across this epic http://www.eagle3.net/n4ywn/docs/PracticalAntennaHandbook-vol4.pdf such a loooong mine of information. In the mighty tome the formulas for calculating the half and quarter lengths of antenna seem to be at odds with Devonians numbers. Not by a lot but there seems to be a great deal of emphasis placed on accuracy when constructing antennas by some and others claim a cm or so makes little difference. What's a poor Electrical Engineer to do when faced with contradictory information particularly when dealing with a rigorous engineering discipline that should not be open to such wide interpreted differences.
I think I might buy one of Flytrons rf to voltage converters and start cutting bits of wire by trial and error and so doing optimizes at least one variable i.e. the length.
Then again perhaps life's a bit tooo short I will just throw my PayPal account at the problem ;D

Regards


John

[phibin]

i have had some OLRS bits for a while and have had a load of problems,
most of seem to have been me in the end! haha  :-[

the biggest problem seems to have been my old 9vap tx !!!
very strange really, the ppm stream out of it maybe???
but it works AOK on my new 9C so all is good i think now.

john aka papa, has been amazing and has given me a lot of time and help with it,
for which im eternally greatfull, its a really good system!

he flashed my HW with 3.6 6ch hop 459 and it seems SOLID so far,
i have done a few tests with a multimeter plugged into the rssi on the ground.

this gave some very interesting results!!!
i purchased some bespoke antennas from a company, they made them lighter for me...
when i used http://www.csgnetwork.com/freqwavelengthcalc.html
then mesured the antennas i had, none seemed the correct lengths!!!
even some that were purchased from firstpersonview (not originally by me, 2nd hand for me)

so i got some sma connectors soldered a bit of wire in the end,
then measured the correct length and cut it...
this has given the best results so far and has no 'ground plane'
next test for a fixed wing application will be a di-pole.

so had my first flight test with olrs today on a quad,
was very happy with it! not a single twitch :)
i was watching the rssi value very carfully to start with in the osd

http://youtu.be/DZNvFWZhCWc

really very happy with it now :)
but on a system like this, a good antenna seems essential really to get the best you can out of it.

cant wait to start pushing the distance with it now  ;D

simon.

[simondale]

when i used http://www.csgnetwork.com/freqwavelengthcalc.html
then mesured the antennas i had, none seemed the correct lengths!!!
even some that were purchased from firstpersonview (not originally by me, 2nd hand for me)

Response from our engineer:

The calculated length does not take into account the sleeving used in the construction and its dielectric impedance.  Optimising the antenna cannot usually be done by simply snipping the wire at the calculated length if it is then going to be encased in a sleeve.   

:-)

[simondale]

Also, we had 100 Diamond Antennas delivered last week. Here they are: http://www.firstpersonview.co.uk/antennas/433mhz/diamond-srh771-sma-433mhz-antenna

All the best

Simon

[WSWhitby]

John Don't apologies,
This is supposed to be a Hobby and as one of my Grand Kids keeps telling me "Get a life".
Like the idea of up the vertical stabilizer, sounds like the name for a Carry On Film but I am sure you know what I mean. Do you mount the Rx close to the dipole with a short coax feed or the Rx further away and use a long coax feed. Wont work quite as well on my Hex or Quad but I don't need the range on either so that's some thing to bring up on another forum some time. Glad phibin has got his "Ducks in a line" my turn next....watch this space. Meanwhile ordered one TX and Two Rx's from HK to cheap not to, back order but with the dreaded Festive season on its way and at least 3 weeks work to do that wont be a problem.

Thanks for replays

Regards

John

[WSWhitby]

Hi Simondale,
Does your engineer have any comments about a 433 MHz being used a 459 MHz, only a a 6% change I agree, and as one of our contributors commented probably only 1 cm. However if its not important one wanders why antennas are cut to different lengths. If one cuts lengths of the conductor and does not effect dialectic, screen  ect then I think you can still optimism an antenna in this rather hit and miss way, MHO. Your case and blatant advertisement  ;)  is however enough to to persuade me  to revert to plan B throw some money at the problem.  :-\

Regards

John

[WSWhitby]

Hi phibin,
Your research seems to back up what I am finding, the lengths quoted in some posts on his forum seem to be in error, not by a large amount, but not correct. Its great to hear that some one who has cut some wire to the "correct length" and has got some good results. Also interesting is that that some professional made antenna's are not the correct length, could it be that the professional antenna are all cut to 433 MHz ? and we have this bizarre situation that a lot of effort seems to have gone in to testing systems at 433 MHz as "A comparison with the legal 459 MHz" and perhaps the 433 and 459 have some how merged in the detail.
Who knows???

Interesting

Regards

John

[phibin]

the length of the antenna will be different depending on the Ø of the wire and the insulation around it!

as true as this is, some antennas do seem quite far off the length you would expect...

and sorry simon, i wasnt knocking your stock..

only mentioning that the 2 'tuned' antennas i have for 459 that originally came from you,
seem to be slightly off the length, in fact they are different from each other so....?
i cant see this being down to differing materials in the 2 identical antennas????

maybe just a bad pair?

i do use one of these on the tx, but in tests with the other one and my home made,
on the rx the home made is gives better results...

anyways, i think i will be investing in a diamond whip for the tx soon,
i will check your site out simon ;)
a lot of people sing its praises inc. papa so thats good enough for me!

i will be doing some more quad testing first,
as i can edge further and further away and keep an eye on the rssi
when i cant go further with the quad, i will start with the fixed wing testing and better antennas.

simon.

[simondale]

Sander published the specifications for these "Sander style" antennas and changed his mind on the length they should be for 459MHz at least once - due to his testing with different materials. We changed the length in line with "the designers" spec. changes.

There's a thread on fpvlab or RCGroups which chronicles the development/ history/ changes that Sander published.

I have asked ImmersionRC to get the manufacturer that makes the new 433MHz antennas that now come with the EzUHF receivers to make us some special 459MHz versions.

All the best

Simon