|Aug 14, 2008, 09:37 PM|
|Aug 15, 2008, 03:04 AM|
have not got a chance to lay my fingers on a 9C yet,
but it is planed with a clubmember that own one, then I can test it and repport back,
but if the PPM and power is similar to other allready tested Futaba systems,
it should work too.
PS thanks for all the orders and pre paying customers,
I will keep you updated here when any news arrives to me,
I am still eger to get the last most-wanted parts end of next week !
|Aug 17, 2008, 10:11 AM|
>Do the receivers have a programmable failsafe?
what do you mean by programmable ?
the fail safe works as explained in the manual, the idea is to prevent lockup,
when/if noise is stronger than signal, the checksum will not be correct and servo positions will not be updated, so after a number of bad pakages the receiver will recall the stored failsafe positions for all servos, the uses will store the servo positons using the pushbutton on the TX unit. When a good parcel is received, servoes will be updated again and error counter zeroed.
I have also today updated the booster page,
added more technical stuff, power vs supply voltage
and info about the cables and such, comments welcome as always:
I have purchased a s***load more of those poweramplifier chips they are quite versatile can be used for many other longrange telemetry projects using the 70cm band,
potential customers please write to : thomas at webx dot dk
|Aug 17, 2008, 09:21 PM|
I almost decided not to post this but I think I will anyway.
Being a new ham operator and having made a j-pole antenna for the 2m band like jettpilot did for the 6m band I have come to understand how antennas work and also how easy it is to make one that will do what you want it to do without spending a fortune on commercial antennas. Especially since I have bought an antenna analyzer that measure swr and impedance.
So for the 70cm band, the antenna would be physically a lot smaller than any other antenna you might build for the 72mhz or 50mhz band commonly used for rc control. Since it is smaller it would be more convienent to haul around and lends itself for experimentation.
I view the rubber duck on Thomas's control unit as a convienence only, it can't be that efficient. An external j-pole would be a considerable improvement but still not very big at a maximum of 1.75 feet long not counting the mast section. Here's a j-pole calculator with instructions on how to make one for any frequency:
This is an omnidirectional antenna with a slight amount of gain that requires no ground plane and in fact will be affected by nearby objects within half a wave length. I have seen this on my swr meter while putting it up on a mast. On 2m with 5 watts I can talk across 14 miles.
It you want more gain at the expense of directivity, the moxon rectangle is another easy one to make that has about the same beam pattern as a patch antenna. Here is a calculator for a moxon antenna for any frequency and most any common materials such as wire or pipe:
This site also contains more details on how a moxon works and what to expect from it. See the attached picture of just how small this would be.
I think either of these antennas used with Thomas's Sherrer's system would give the range you're looking for with the convienence of not having a big bulky antenna to haul around.
|Aug 18, 2008, 03:00 AM|
thanks for your input Carlyle, you are most welcome :-)
where are you from ? you forgot to fill in your location.
yes you are right with know-how and antenna understanding users can come along way, I have seen ham radio freaks construct extreamly complicated antennas just to get the last db no one could hear anyway :-)
the idea about the cheap whip (supplied) is to get enought range for most people,
and not directional, so no big issue where it points, I think that is best in the beginning.
if people wants more range they can order more power or use directional antenna
or even both :-)
10dB more power = 3 times the range, and 10dB gain is easy to get using antenna pointed to plane, and this will also give you 3 times the range, but you need a helper to point the antenna or only fly in that one direction you have mounted the antenna, or invent tracking system.
as a radioamateur you use 2m and 70cm alot for local talk
(that is 145 and 435MHz band)
the antennas most people use have much more gain on the 70cm band,
but the range on 70cm is still much less, compared to 2m band !
that is due to the 3 times higher frequency, as we all know higher frequency have shorter range ! range calculators exist online try to experiment with input data and see hos many extra dB power is needed 3 times the frequency to achive same power at the receiver side.
I have already explained bandwidth and receiver sensitivity a few pages ago :-)
so you cant compare secitivity on video receivers and RC receivers, video is 1000 times wider ! so we should expect it to read 30db worse on the sesitivity value
|Aug 18, 2008, 08:50 PM|
Amp for 434MHz
In the USA you do need to be a Ham operator to operate that freq.
I don't know about you over there. Here is one for you ,it is cheap so so
$57 US it will take 100mw and make 60watts. the unit is a module SAU82L
Like your 707. You can get it from www.RFPARTS.com It needs 12 volts
0 to 5 volts for bias one RF input and one RF output. and you'll need a
good heat sink. With 15 amps of current at 12 to 16 volts is a lot of
heat to get rid of. I use a pair of them I get 120 watts output. A single
unit is easy to build. You can take a double sided PC board and cut the
copper off to make the board. in 15 minutes. The only big thing is the
heat sink of the module has to have a good RF connection on both screw
mounts to the PC board.
Any one that would use it to fly a RC here state side would be a fool.
There are Hams that run a full KW on 427,436 and 439 Mhz for TV.
Us Hams transmit TV picture on that band all the time. +- 6Mhz video.
|Aug 18, 2008, 09:14 PM|
Antennas for 70cm
Here is an antenna that the US Hams use for TV mobile. We also
use it on TV transmitters on balloons that go up to 70,000ft. with
video camera on board.
It called a A 70cm Big Wheel Antenna
You can find the plains at.
It is only 6 inches across and is a Horizontal Antenna. Would make a nice
antenna to hang under the Plane .
|Aug 19, 2008, 01:20 AM|
Hi charles thanks for your input. Happy to see so many radioamateurs like my self also enjoy FPV and RC models, I am OZ2CPU see more at www.webx.dk
cool link to the 60W PA device, most radiamateurs will have to skills to make this one run, but many FPV'ers need a bit of assistance I think, so that is why I make and sell a 100% ready to fly booster, with tested harmonics filter and proper designed input attenuator.
>In the USA you do need to be a Ham operator to operate that freq.
I can use any frequencyes the customers prefer in the 410 to 450Mhz band
I can use any frequency hopping system I like, and even different bandwidth in the FM modulation, it is possible to find free unused space and use it (not legal offcourse) but again it is also possible to drive your car with out the seat belt, that is also not legal.
it is cheap and easy to get a licence, I offcourse encurage people to drive and fly legally.
>Any one that would use it to fly a RC here state side would be a fool.
why ? this system uses frequency hopping spread spectrum, so it is (almost) impossible to shoot it down :-) but ofcourse if you fly near a ham opperators house and he tx 1kw even near your used frequency band the LNA will most likely be overdriven and you loose RC, same issue with any other RC brand on the marked,
ham opperators can tx 250W on the 2.4 video/RC band, and other services can tx in the 35MHz -72MHz band even from another contry due to the HF/VHF skips and this can also jamm your range, so offcourse only a wired connection is 100% secure.
we always have to live by that fact, and also no model planes last forever !
many other things can and will go wrong if you wait long enought.
Love the wheel antenna, should be really nice to see some scaled plans for 900 and 2.4 too :-) only problem is the trimmer capacitor the value is a bit critical om 70cm
I bet it will be even harder to sort it for beginners on 2.4 without access to network analyzers.
|Aug 19, 2008, 01:40 AM|
here is this wireless calculator I have mentioned before:
free space loss at 10km (6.2miles) line of sight best case !
35MHz = 83.3dB
72MHz = 89.6dB
145MHz = 95.7dB
435MHz = 105.2dB
900MHz = 111.5dB
2400MHz = 120dB
5600MHz = 127.4dB
so if you x3 the frequency, your attenuation will be 10dB more = 1/3 the range
using same gain antennas and same tx power and same receiver sesitivity.
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