2.4Ghz system differences

[DirtyBoy]

While we here in SIN are blessed with the availability to use all the 2.4GHz available (DSM, DSM2, DSMj and FASST). It leaves us with the question of which system to choose..
FUT fans will obviously stick with the FASST system.. but what of the rest?
Here's what i have found and pls correct or contribute this thread for the benefit of everyone

1. DSM2: hops between just 2 freqs and has a max transmission power of 100mw
2. DSMj: hops throughout the 2.4GHz spectrum and has a max transmission power of just 3mw (meeting the JDM rules)
3. FASST: hops throughout the 2.4Ghz spectrum, but what's the transmission power?
4. DSMj and DSM2 are not compatible due the the freq hopping characteristics

Q: What would the transmission power mean in terms of range and/or intergrity? less power = less range?

N.B. those looking for JR radios be careful as some are DSM2 (spektrum compatible) and some are DSMj (JR only) technology..

Anyone with any more info on the topic?

[Super-Hornet]

Another one by Hitec:
AFHSS (Adaptive Frequency Hopping Spread Spectrum)

http://www.hitecrcd.com/receivers/show?name=Spectra+2.4%2FOptima+7+Combo

http://www.hitecrcd.com/transmitters/show?name=Aurora+9

From:

http://en.wikipedia.org/wiki/Frequency-hopping_spread_spectrum

"Adaptive Frequency-hopping spread spectrum (AFH) (as used in Bluetooth) improves resistance to radio frequency interference by avoiding using crowded frequencies in the hopping sequence. This sort of adaptive transmission is easier to implement with FHSS than with DSSS.

The key idea behind AFH is to use only the “good” frequencies, by avoiding the "bad" frequency channels -- perhaps those "bad" frequency channels are experiencing frequency selective fading, or perhaps some third party is trying to communicate on those bands, or perhaps those bands are being actively jammed. Therefore, AFH should be complemented by a mechanism for detecting good/bad channels.

However, if the radio frequency interference is itself dynamic, then the strategy of “bad channel removal”, applied in AFH might not work well. For example, if there are several colocated frequency-hopping networks (as Bluetooth Piconet), then they are mutually interfering and the strategy of AFH fails to avoid this interference.

In this case, there is a need to use strategies for dynamic adaptation of the frequency hopping pattern.[3] Such a situation can often happen in the scenarios that use unlicensed spectrum.

In addition, dynamic radio frequency interference is expected to occur in the scenarios related to cognitive radio, where the networks and the devices should exhibit frequency-agile operation.

Chirp modulation can be seen as a form of frequency-hopping that simply scans through the available frequencies in consecutive order."

[DirtyBoy]

super-H,
a radio guru indeed .. i've seen cordless phones move from 2.4 to 3.6 to 4.2 to 5.8Ghz, do you know why the RC industry chose 2.4 Ghz? 2.4 it seems a bit congested with everything from wi-fi to phones.. my wi-fi at home used to get disconnected everytime i used my 2.4Ghz cordless phone..
jus curious why RC chose 2.4Ghz instead of other available freqs.. also do you know what the transmission power for futaba FASST system is?

[DirtyBoy]

also the futaba FASST system claims good signal integrity without the need for satelite receivers.. does anyone know why and how true this is?

[aeromech]

Bros,

for what i have learned before during my radio transmission days where we used to use the FM band transceivers like kenwood and icom. .the lower the frequency the longer the radio wave is and the higher the radio frequency the shorter the radio wave would be and this means that if you used 2 different band like am and ghz at the same power output let say 1 watt. .the am band tx would tend to reach farther than the Ghz tx due to wave lenght factor and obstacles. .what i have experience before is that 2.4Ghz transmitting with buildings in between each othere would tend have higher interference than an Am unit coz 2.4Ghz and above has like the line of sight aspect and lower frequency tend to have penetrating aspect. .so going higher in the radio band spectrum above 2.4Ghz would may cause some problems or some sort due to alot of factors

actually the lenght of our antennas for our receivers (e.g. 72Mhz) is not enough to provide adequate reception receiving coz if you follow properly even using the quater wavelength frequecy your antenna suppose to have 39.5 inches in length


this is what i have learned before and if any of the statements here is in a way not correct pls advice me so i can correct them. .thanks for reading

[Super-Hornet]

I no "radio guru" or in any way...
U place me too high!

Anyway, from what I know,
Our R/C TX has a maximum limit of transmission wattage it allow to use. This is controlled by some telecommunication regulatory bodies.

http://en.wikipedia.org/wiki/List_of_telecommunications_regulatory_bodies

Thus, in order for that device to use in that country (or able to sell in that country), it must approve by the regulatory groups.

That mean, those that is branded or international recognize should follow the rules set up by the groups. In other word, Futaba, Hitec, JR should be around the same wattage. Those that is unbranded or don't care about any regulatory group may have its wattage higher than other brands.

Frequencies above 1GHz tend to have more cleaner signal. If u use spectrum analyzer, it will notice that those radio signal above 1GHz tend to be cleaner.

Good:
------
The good thing about higher frequencies (like comparing MHz to 1GHz to 2.4GHz to 5.8GHz) is that, the higher the frequency it is, the wider/bigger the bandwidth it can have or carries. In other word, u cannot transmit 1MHz data over 100kHz transmission right? Because of that, the higher bandwidth it allow to transmit, the faster baud rate (bit per second) it can transmit (digitized voice in phone or video, faster speed in PWM and so on).
Another good thing about higher frequency is that it allow to use much shorter antenna.

Bad:
-----
The bad point of using higher frequencies is that, it is much difficult to design and develop (manufacture). This is because of when frequencies goes up, small capacitance (Farad) or inductance (Henry) can easily affect it. In the electronics circuit board, 2 copper track or 2 wires running together in parallel can easily cause capacitance effect. Copper tract or wire goes in the loop can easily cause inductance effect. That is why the higher the frequency, the more complicated the circuit design become. This may explain why those cheapo GHz TX/RX tend to fail or has poor transmission or easily suffers from interference.



The higher the frequency, the higher the penetration it become. When high frequency hit obstacle, it tries to penetrate over. Each time it penetrate something, it lost some of its sign strength. When low frequency hit obstacle, it bounce away. That is why X-Ray can penetrate human tissues/bones (X-Ray is in GHz range). That is why GHz phone (non DECT type) do not have interference across rooms. Those short wave (SW) radio broadcasting is transmit in lower frequency. Why u can hear SW radio from long distance is because the signal get bounce around by our ionosphere. Those satellite transmission do not get bounce around because it is transmit in GHz and thus it penetrate the ionosphere.

Because of higher frequency penetrate, that is why marine (ship) communication is using low frequency as compare to airplane because it need the signal to get bounce around. Because of that, actually for land and water base R/C, it is better to use low frequency instead. Maybe that is why some experiencing control lock out when they use 2.4GHz for water base R/C.

Note:
By having faster PWM, your stick movement in TX to RX can be faster. Faster PWM also allow u to transmit more channels. Our TX channels is transmit serially. Take example, Channel 1 is encode 1st followed by Channel 2 and so on into a PWM like signal before it fed into FM/AM transmitter in our TX.
Because higher baudrate it can transmit, the higher bandwidth it has.
Higher frequencies also allow channels (Transmitting frequencies channel) to place apart. Thus, reduce the cross over effect.

[misato]

Bros,

for what i have learned before during my radio transmission days where we used to use the FM band transceivers like kenwood and icom. .the lower the frequency the longer the radio wave is and the higher the radio frequency the shorter the radio wave would be and this means that if you used 2 different band like am and ghz at the same power output let say 1 watt. .the am band tx would tend to reach farther than the Ghz tx due to wave lenght factor and obstacles. .what i have experience before is that 2.4Ghz transmitting with buildings in between each othere would tend have higher interference than an Am unit coz 2.4Ghz and above has like the line of sight aspect and lower frequency tend to have penetrating aspect. .so going higher in the radio band spectrum above 2.4Ghz would may cause some problems or some sort due to alot of factors

actually the lenght of our antennas for our receivers (e.g. 72Mhz) is not enough to provide adequate reception receiving coz if you follow properly even using the quater wavelength frequecy your antenna suppose to have 39.5 inches in length


this is what i have learned before and if any of the statements here is in a way not correct pls advice me so i can correct them. .thanks for reading

To add on, higher frequency tends to loss more power over given distance then a lower frequency. Frequency dispersion/absorption from elements like air/water vapour/etc is also more prominent as frequency increases. Penetration also weakens as frequency gets higher. As such with so many factors, it seems using 2.4GHz might seems a bad idea compared to 35/72MHz.

Not really. As frequency gets lower, the larger the wave gets. Matching the antenna to the frequency will give good sensitivity/power/SNR perimeters. Mismatched antenna will often results in power performance in range and higher signal loss. For a 72MHz band, optimal antenna should be in the range of 38" to 44" in length for both TX and RX sides. This explains why the antenna were always that long in our Radio system. Long antenna also means more weight and exposure to distortion. 2.4GHz on the other hand needs only 5cm of antenna.

Another the point to note is frequency speed in ratio to usable bandwidth for data traffic, and latency in transmission. In the 72MHz radio, it has 49 non-lapping channels. Each channel has 20KHz of bandwidth to carry data. If we use 20KHz per channel, a 2.4GHz system will have 50,000 20KHz channel to use. Known definition for 2.4GHz (based on WIFI 802.11b standards), will be 11 Channels, each channel will have 9MHz bandwidth for data. Meaning more control commands can be transmitted in a single frame compared to a 72MHz setup. This results in lower latency in execution of a given command, ie moving of cyclic servo, or complex servo mixing execution.

http://radiocontrol.wikia.com/wiki/72_MHz

[aeromech]

SH your rite in those statements. .and the more u go higher in the band spectrum the more expensive the modulating unit would be because of the complication of design and other factors. .where ever you go. .27 and 29 are always used for land based or surface transmitter due to its transmitting characteristics

bro SH what is your comment on my moded 6EXHP. .honestly im in a tight budget rite now so i have to go in anyways or means to be able to have a 2.4Ghz tx and have a better reception and glitch free . .

[Super-Hornet]

I just starting to use 2.4GHz also (Aurora 9)...so I not sure which one is better.
I believe all branded should be O.K. right

Anyway, if u have Hitec Optic 6 or Futaba TX, maybe the cheapest to go 2.4GHz maybe by using Hitec Spectra 2.4GHz:

http://www.hitecrcd.com/receivers/show?name=Spectra+2.4%2FOptima+7+Combo

Rotor selling at SGD147.20
http://shop.rotor.com.sg/show-detail.asp?prodid={2D5E5FCD-2844-4FA6-8110-713D5C5DD2BE}&pn=

The only problem of using this is that:
1. U still using your old TX
2. Rotor do not have any stock for Hitec 2.4GHz RX YET! That mean u only have 1 RX that come with this combo. U want more RX, u need to source it overseas or wait.

If not, then u have to get either one of the above (1st post, that is, JR, Futaba or Spektrum?). But I think their RX is more expensive that Hitec right?

SH

[zxyong]

The "less glitches" thingy is because 2.4Ghz radios uses techniques like DSSS FHSS, which have redundancy.

Mhz radio uses simple direct link, no redundancy. If you can use DSSS on a 72Mhz band, it will have lesser glitching problems too.

[aeromech]

Bro SH,

mine is 2.4Ghz and 72Mhz dual bander tx already i finished the mod the other nite. .it cost me around $100 and i have the best of both worlds in my tx coz i can use my 72mhz rx and 2.4ghz rx anytime i want and would save me alot of money

the range of my 2.4ghz is aroung 300m to 800m+ depending on the rx (can go 3km+ if needed) but for my point of view. .flying beyond 300m with a 60 size plane would be nuts even you have a good eyesight unless you are using FPV system. .

bro attached pic is the aluminum retractable antenna for 72Mhz and a 45º rubber ducky for the 2.4Ghz and the green LED if the 2.4Ghz is active

[Ghostfit]

While we here in SIN are blessed with the availability to use all the 2.4GHz available (DSM, DSM2, DSMj and FASST).

Where is your black and white on this ???


...not being confrontational or anything ! ....I was just wondering.

[fuse]

ida has approved spekrum dsm2 fqn, but not other 2.4 radios yet.

[DirtyBoy]

Where is your black and white on this ???


...not being confrontational or anything ! ....I was just wondering.

Spektrum uses DSM/DSM2
JR has both DSM2/DSMj
Futaba uses FASST system..

is that correct? all these systems are available for purchase and use in SIN unless i am going crazy seeing things..

[DirtyBoy]

...ok i may be wrong on the "to use" part but they are certainly "available" here in SIN...

..and thks for the invaluable info guys.. guess when it comes to manufacturing cost is the first priority (which explains why the 2.4GHz choice)...