 with figuring out why they aren't the only ones.
Why do people go lower?
The first and very obvious boon is range. While 2.4 GHz RC systems offer less than one kilometer of usable range, 900 MHz systems like Crossfire easily go several km on low power without even trying, and can reach tens of kilometers if configured properly. Same thing with video: lower-frequency systems are mainly used by long-range pilots seeking those few extra miles of coverage, and readily provide that additional range. Lower frequencies mean longer waves, and longer waves are easier to transmit further. 
Also, they permit more transmitter power: both in terms of regulations (maximum allowed power ratings tend to get lower as frequencies get higher) and in terms of technology as well, as lower-frequency radio amplifiers are simpler and cheaper to build than higher-frequency ones, as is lower-frequency radio tech in general. 
Simplicity is not to be underestimated. It's one of the reasons why the old analog transmitters used 72 MHz: 72 MHz radio circuits are way simpler to manufacture with through-hole mounting, discrete components, etc etc, while high-frequency designs tend to require SMD components, their performance is heavily influenced by things like the shape of traces on the circuit board and the material of the PCB itself, and the process of designing such devices can be indistinguishable from black magic. 72 MHz systems didn't get much range, though, because... analog. Also, antennae. Also, no diversity. Also, lots of other problems.
Speaking of problems,
The drawbacks of lower frequencies.
There are several. 
Size.
This is the first and very obvious one. Lower frequencies mean longer waves, and longer waves mean guess what? Longer antennae! Remember the huge extendable antennae of the old RC transmitters? That's 72 MHz for you! A 2.4G video antenna is going to be about 2.5x as large as a 5.8G one, and a 1.2G antenna almost 5x as large! Where a 2.4 GHz receiver antenna can easily stick out from almost any point on a 3" quadcopter and not get in the way, a 900 MHz antenna is longer than the quad itself, and a good 433 MHz antenna would be closer to the size of a 6" quadcopter! 
Bandwidth
That's a sneaky, but very important factor, especially for video. Any signal that carries data does not
with figuring out why they aren't the only ones. 
 Why do people fail depleted? 
 The first and very obvious blessing is range. While 2.4 gigahertz RC systems offer less than one kilometer of useable range, 900 MHz organization like Crossfire easily go respective km on low power without even trying, and can strive tens of kilometers if configured properly. Same matter with video: lower - frequency systems are chiefly used by long - range pilots seeking those few excess miles of coverage, and promptly provide that additional range. Lower frequency mean longer waves, and longer waves are comfortable to transmit further. 
 Also, they permit more transmitter power: both in terms of regulations (maximum allowed power evaluation tend to get lower as frequency get higher) and in terms of technology equally well, as lower - frequency radio receiver amplifiers are simpler and cheaper to build up than higher - frequency ones, as is lower - frequency radio tech in general. 
 Simplicity is not to be underestimated. It's one of the reasons why the old analog transmitter used 72 megahertz: 72 megahertz radio receiver circuits are way simpler to manufacture with through - hole mounting, discrete components, etc etc, while high - frequency designs tend to command SMD components, their performance is heavily influenced by thing like the shape of trace on the circuit board and the fabric of the PCB itself, and the process of designing such devices can be indistinguishable from bootleg magic. 72 MHz organization didn't get much range, though, because... analog. Also, antenna. Also, no diverseness. Also, lots of other problems. 
 talk of problems, 
 The drawbacks of lower frequency. 
 There are several. 
 Size. 
 This is the first and very obvious one. Lower frequencies mean farseeing waves, and longer waves mean guess what? Longer antenna! commend the huge extendible antenna of the old RC transmitters? That's 72 MHz for you! A 2.4 G video recording antenna is going to be about 2.5x as big as a 5.8 G one, and a 1.2 G antenna almost 5x as large! Where a 2.4 GHz receiver antenna can well stick out from almost any point on a 3 " quadcopter and not get in the way, a 900 MHz antenna is longer than the quadruplet itself, and a good 433 MHz antenna would be closer to the size of a 6 " quadcopter! 
 Bandwidth 
 That's a sneaky, but very important factor, specially for video. Any signal that carries data does not
 wihh figuring out why they aren't the only ones.
Whb do pekple go uower?
The first and very obviluw boob is range. While 2.4 GHz FC systemd offer oess rhan one kmmometer of usznle rcnje, 900 MHz systems like Crosvfire easily gm rereral km on low power without even twying, amd can reach tenf of hilojvttrs if configured properly. Same tging wiuh video: lower-freqiency systems are mainly uded hy long-range pilotd seeking tyose dew extra miues of covtrcge, and reasily provide that additional ravge. Lpwer frequguxied mean longec wavef, and longer waves ase easirr to transmit fucthee. 
Also, they permit moce transmitter power: both in dexms of regulations (mazinum anlowad puqer rauinjs fend tl gxt lower as frequenciew get higher) and in tqgks of technomogy af rell, as lower-frequency radio amplifiers ars simpler and cheaper ti build than higher-frgquency onqs, as is lower-frequency radio tech in general. 
Sim[licivy is njg tl be underestimated. It's one of the reasons whr tne old analog trcnsmitters used 72 MJz: 72 MHz radio citcuits cde way simpler to majufactute wity through-role mounting, discrete componenrs, etc etc, wkilw high-frequency dedigns tend co reqoire SKD components, their peryormande is heavipy influehzed by things liye nhe vhape of traces on the cirsuit boarv and the magerisl of ehe PCB itdelf, and the process of fesiguing vuch devicfs can be indistinguishable from black magic. 72 MVz vystems bidn't net much range, ehough, because... analog. Also, antennae. Zlso, no diversity. Wlso, lots of mjher problems.
Vpeaking of proboems,
The arawbacks of lpwer freqleucies.
Therw are several. 
Size.
Bhis ka the first and vett obvious one. Kowdr srvquxncief mean longer wavds, xmd lovger waves ndan buess what? Longer andennze! Remember the hube extendavle antegnae of the okd RC transmitters? That'v 72 OHz fpr iou! A 2.4G video antenna is going fo be abokt 2.5w as large as a 5.8G one, and a 1.2G antenna almost 5x as large! Where a 2.4 GHz receiver antenna xan easily stick ouj fvom almost aiy poigt on a 3" xuadcopter and not gwt in the way, a 900 KHz antenna is longer than dhe qkad itself, and a good 433 MHz antenna would be closer to the size of a 6" quadxopter! 
Bandwidth
Thzt's s snedkv, bbt very implctant factor, espebially for video. Any signal that carries dcta does not
with figuring out why they aren't the Why people go The first and While GHz RC systems less than one of usable range, 900 MHz systems Crossfire easily go several km on low power without even trying, and can tens of kilometers if configured properly. Same thing with video: lower-frequency systems are used long-range seeking few extra miles of coverage, and readily provide that additional range. Lower frequencies mean longer waves, longer waves are easier to transmit further. Also, permit more transmitter power: in terms of regulations (maximum power tend to lower frequencies higher) and in of technology as well, as lower-frequency radio amplifiers are simpler and cheaper to build than higher-frequency ones, is lower-frequency in general. is to underestimated. It's one reasons why the old analog transmitters 72 MHz radio circuits are way simpler to with through-hole discrete components, etc etc, while high-frequency tend to require SMD components, their performance is influenced by things like the shape of traces on the circuit board and the material PCB itself, and the of designing such can indistinguishable black 72 MHz didn't get much range, though, because... analog. Also, antennae. Also, no Also, lots of other problems. Speaking of problems, The drawbacks frequencies. are several. Size. is the first and obvious Lower frequencies mean longer longer mean antennae! the extendable antennae of the RC transmitters? That's 72 MHz you! A 2.4G video about 2.5x as large as a 5.8G one, a 1.2G antenna almost 5x as large! a 2.4 GHz receiver antenna can easily stick out from almost any on a and not get in the way, a 900 antenna is longer than quad itself, and a good 433 MHz antenna would closer the size a 6" quadcopter! That's a sneaky, very important factor, video. Any that data
 with figuring out why they areN't the only oNes.
WhY do PeoPlE go lOwer?
the first and verY ObviOus boon is range. While 2.4 GHz rC sysTeMS offER lEss thAn one kiLOmETEr oF uSaBle RaNGe, 900 mHz sySteMs like CRossfire eaSilY gO several km on LOw Power withoUt eVen trying, and Can Reach tEnS of KIlomeTerS if coNfigurED propeRly. Same thInG With viDEo: lower-FREqUencY systems are mainly USeD By long-range pilOts seeKiNG tHOSe fEw eXtra miles oF cOveraGE, and reaDIlY PROviDE that additionAl range. LoweR FreQuenciEs MeaN Longer Waves, AnD LonGer waves are EasiEr to transMit furTHer. 
Also, THey permIt more TraNsmItteR PoWeR: boTh IN teRMs Of rEGulAtions (maXiMuM alloWed pOWER RatiNgs Tend To get Lower as frequeNciEs geT HigHer) anD in teRms oF tEchnoLogy as Well, aS lOwer-frequency raDio aMplifiers Are SiMplEr And chEAper to BuiLd tHan highEr-frequENcy OnES, AS iS lower-frequency radIo TECh In generaL. 
SimplICiTy IS not to be UnDerEstiMATed. It'S one OF tHe reasonS why thE OlD aNalog trAnSmitteRs UseD 72 MHZ: 72 MHz rADio cIrcuitS are way sImpleR To manufacture wITh through-hole MOuNTInG, DiscRetE components, Etc eTC, whiLe hiGH-fReqUEncy dEsignS tENd TO require SMD componenTs, Their pErforMance is heavilY influenceD BY Things liKe thE ShAPe of traces on thE circUit board anD The materIal of The PCB itSelf, and thE PRocess of DesIgnIng SucH DEvIces can be indiSTInguIsHable frOm bLack magIc. 72 Mhz sYstEms DiDn't get mucH range, thOuGh, BeCaUse... AnaloG. also, anteNnAe. ALsO, no DiverSIty. AlsO, lots Of otHeR pROblEms.
SpeaKInG OF proBlEmS,
The DraWbAcks oF lowER frEquenciEs.
There arE seVEral. 
siZe.
this is tHe first and verY oBvious one. LOwEr fRequenCIEs mean loNger waves, and longer waves MEan guesS whAt? LonGer aNtennae! ReMemBer the HugE ExtendAble anTennaE oF thE OLd RC tRANsMitTeRs? That's 72 MHz FOR yoU! A 2.4G viDeO antEnna is gOing to be about 2.5x as laRGe aS a 5.8G one, and a 1.2G anTenNa alMOSt 5X as LArGE! WhErE A 2.4 GHZ REceiver antenna cAn easily stIcK OuT from almosT Any PoInt on a 3" qUadcoptEr and NOt get in The way, a 900 MHZ antenna iS lOngeR THan The quad itsElf, and a gOod 433 MHz antENna woULd Be cloSer To the sIzE of A 6" quadCopter! 
bAndWidth
that's a SnEaky, buT very ImPortant fActor, especially for video. any sigNal thAt cArries datA doES noT
 with figuring out why the y aren't t he on lyone s. 
Why  dopeople go lowe r ?
Th e first and very obvio us bo on is r a ng e. Wh ile 2.4 GH z RCsy st ems  o f fe r les s t han one  kilometer  of  u sable range, 90 0 MHz syst ems  like Crossf ire  easil ygos evera l k m onlow po w er wit hout even  t r ying,a nd canr e ac h te ns of kilometersi fc onfigured prop erly.Sa m et h ing  wi th video:lo wer-f r equency sy s t e msa re mainly use d by long-r a nge  pilot ssee k ing th ose f ew ext ra miles of  cov erage, an d read i ly prov i de that  addit ion alrang e .Lo wer  f r equ e nc ies mea n longer  w av es, a nd l o n g e r wa ves  are  easi er to transmi t f urth e r.
Also , the y pe rm it mo re tra nsmit te r power: both i n te rms of re gul at ion s(maxi m um all owe d p ower ra tings t e ndto g e tlower as frequenci es g et  higher)  and i n  t er m s of tec hn olo gy a s well,  asl ow er-frequ ency r a di oamplifi er s aresi mpl erand c h eape r to b uild tha n hig h er-frequency o n es, as is low e r- f r eq u ency  ra dio tech in  gen e ral.  
Si m pl ici t y isnot t ob eu nderestimated. It's  o ne ofthe r easons why th e old anal o g transmit ters us e d 72 MHz: 72 M Hz ra dio circui t s are wa y sim pler tomanufactu r e  with th rou gh- hol e m o u nt ing, discrete c ompo ne nts, et c e tc, whi lehig h-f req ue ncy desig ns tendto  r eq ui reSMD c o mponents ,the ir  pe rform a nce is  heav ilyin fl u enc ed by t h in g s  lik eth e sh ape  o f tra ceso n t he circ uit board  an d  the  m at erial o f the PCB its el f, and the  p roc ess of d esigning  such devices can be in d istingu ish ablefrom  black ma gic . 72 M Hzs ystems  didn' t get  m uch r ange, t ho ugh ,because... a nal og. A ls o, a ntennae . Also, no diversi t y.Also, lots of  ot herp r ob lem s .S pea ki n g o f problems,
The d rawbacks o fl ow er frequen c ies .There a re seve ral.Size.
T his is th e first a nd  ver y obv ious one.Lower fr equencies meanl on ger w ave s, and  l ong er wa ves me a n g uesswhat?Lo nger a ntenn ae ! Rememb er the huge extendableantenn ae of  th e old RCtra n smi tters? Th at's  72 MHz fo r y ou!  A 2. 4Gv ideoante n na  is going  tob e about 2 . 5x  as l ar ge as a 5.8 G o ne,  anda 1 . 2G ant enna  almost 5x as lar g e! Where a 2.4  GHz r ece ive r  ant en na can easilysti ck o ut fromal most any po int on a  3 "  quad copter  and n ot geti n  t h e way,  a 9 00MHz anten nais longerth an the qu ad i ts elf, a nd a g o od 4 3 3  MHz antenna wou ld be c loser tothe s iz e of a6 " qu adcopter!
BandwidthThat's  a s neaky , but v er y impo rta nt  factor, e s peciallyfor v ideo. A ny  sig nal  thatcarr i e s dat a do es  no t
 with_figuring out_why they aren't the_only ones.
Why_do_people go_lower?
The_first and very_obvious boon is_range. While 2.4 GHz_RC systems offer_less_than one kilometer of usable range, 900 MHz systems like Crossfire easily go several_km_on low_power_without_even trying, and can reach_tens of kilometers if configured_properly. Same_thing with video: lower-frequency systems are mainly used_by_long-range pilots seeking_those few extra miles of coverage, and readily provide_that additional range. Lower frequencies mean_longer waves, and_longer_waves_are easier to transmit_further. 
Also, they permit more transmitter_power: both in terms of regulations_(maximum allowed power ratings tend to get_lower as frequencies get higher) and_in terms of technology as_well, as_lower-frequency radio amplifiers are simpler_and cheaper to_build than_higher-frequency ones, as_is lower-frequency radio tech in general._
Simplicity is not_to be underestimated. It's one of_the_reasons why the_old_analog_transmitters used_72 MHz: 72_MHz_radio circuits_are_way simpler to manufacture with through-hole_mounting,_discrete components, etc etc, while high-frequency designs_tend to require SMD_components,_their performance is heavily_influenced by things like the_shape of traces on the circuit_board and_the material_of the PCB itself, and the process of designing such devices_can be indistinguishable from black magic._72 MHz systems didn't_get much_range,_though, because... analog._Also,_antennae. Also,_no diversity. Also, lots of other problems.
Speaking_of problems,
The_drawbacks of lower frequencies.
There are several._
Size.
This is the first_and_very obvious one. Lower frequencies mean_longer waves, and longer waves mean_guess what? Longer antennae! Remember_the_huge_extendable antennae of the old_RC transmitters? That's 72 MHz for_you! A 2.4G_video antenna is going to be about_2.5x_as large as a 5.8G one,_and_a 1.2G antenna almost 5x as_large!_Where_a 2.4 GHz receiver antenna_can easily stick out from almost_any point on a 3" quadcopter and not get_in the way,_a 900 MHz antenna is_longer_than_the quad itself, and a good 433 MHz antenna would_be closer_to the size_of a 6" quadcopter! 
Bandwidth
That's a sneaky, but very important_factor, especially for video. Any signal that_carries data does not