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Question about old FM radios vs new radios

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Old 12-20-2013, 06:50 AM
  #26
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Just to add the counter argument...

2.4 GHz is not a panacea. People do have problems with their 2.4 GHz systems, just like people used to have problems with their 72 MHz systems. 2.4 GHz systems have the important advantage of eliminating frequency conflicts, but the use of 2.4 GHz presents some radio engineering difficulties that require complex solutions in order to make the systems work. 2.4 GHz systems are significantly more complex than 72 MHz and there is arguably more to go wrong.

My point is that the OP should not feel compelled to change his stuff to 2.4 unless he personally desires to make the change. 72 MHz works well and is arguably just as reliable as 2.4 GHz, provided that frequency conflicts are not a problem at his flying site.

Last edited by JPMacG; 12-20-2013 at 06:52 AM.
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Old 12-20-2013, 07:00 AM
  #27
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One thing with FrSky is when performing a range test make sure that you take it off of low power mode before flying. Ask me how I know. It is not like other systems where you have to hold a button down to keep it in range test. After my crash I no longer perform range tests daily. I only do it a few times when the model is new and after that no more. My new DX 18 has built in telemetry so I can view the report about how the link performed after every flight. That is a nice feature to see if there are any issues among the 4 sattelites.
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Old 12-20-2013, 07:53 AM
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Quote:
Originally Posted by JPMacG View Post
Just to add the counter argument...

2.4 GHz is not a panacea. People do have problems with their 2.4 GHz systems, just like people used to have problems with their 72 MHz systems. 2.4 GHz systems have the important advantage of eliminating frequency conflicts, but the use of 2.4 GHz presents some radio engineering difficulties that require complex solutions in order to make the systems work. 2.4 GHz systems are significantly more complex than 72 MHz and there is arguably more to go wrong.

My point is that the OP should not feel compelled to change his stuff to 2.4 unless he personally desires to make the change. 72 MHz works well and is arguably just as reliable as 2.4 GHz, provided that frequency conflicts are not a problem at his flying site.
I disagree.
2.4 is far more reliable than 72. The transmitting protocol is much more complex but that has been worked out years ago and is buried in the chip where its not an issue.
2.4 relieves you of the possibility of being shot down by your buddy.
2.4 contains no fragile crystals or IF transformers.
The processor gain of the spread spectrum system results in a considerable increase in receiver sensitivity. -100 DBM is normally achieved.
The higher frequency makes it nearly immune to local interference such as metal to metal sparks.
The antennas are much smaller and can be easily made redundant
The receivers are much less expensive. There is one available for less tha $8
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Old 12-20-2013, 08:13 AM
  #29
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Go with anything name brand, all of them are good. The cheap chinese stuff has no product support basically, if it breaks or doesn't work you are pretty much out the money you spent on it.
If they were available from "real" hobby shops I would seriously look at one. A radio is not something I'd buy online without at least seeing how it felt in my hands.
Plus as I said above you are paying your money and taking your chances, take a long look at some of the threads regarding these radios, there are some issues with some of them like sticking buttons, bind issues etc.
I'm also not sure if any of them come with the "good" software installed or if everybody has to download and install better software.
Sorry but without some local support/purchasing options I won't touch one.
Cue up the fanboys with the stories about how great theirs is....do yourself a favor and read up as much as possible before you make a choice, then decide.
I'm not against saving money, but I have to actually believe in the product, and sorry to say there are a lot of threads where people are having issues, entirely what keeps me away. Not saying my name brand stuff can't have problems, but I KNOW a resolution is a short drive away where I bought it. Plus I know the company that makes my brand has amazing service, hear about how great it is quite often even though I've never required it. Many threads about free repairs or replacements from the company.
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Old 12-20-2013, 08:59 AM
  #30
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I disagree when it comes to FrSky. There stuff has pretty much been proven and there are very few failures that I am aware of. Everyone seems to love that new Taranis Tx they developed. That and the Turnigy 9X have some pretty loyal followers. Not only that but there are advantages with the open source software they use if you are a tinkerer. You are correct about product support and it is dismal but fortunately none of the FrSky products I purchased ever had a single issue. RC model Reviews did a great test on the FrSky frequency hopping protocol and it appears to be a very robust link. My only issue (and Tx related crash) was when I left it in range test mode for my flight. I saw it going in and out of fail safe mode until it lost all control. Realized about 5 seconds after it hit the ground what I did. DOH!
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Old 12-20-2013, 09:05 AM
  #31
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Default Futaba 9C

I will never give up my 9C super.Am the only one at the field using 72mhz.Use Hitec and Futaba receivers,Love it
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Old 12-20-2013, 09:16 AM
  #32
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My channel 16 Futaba 9C still works perfect and with many people using 2.4, my pin is always free.
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Old 12-20-2013, 09:24 AM
  #33
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Very easy to keep on using a radio such as the 9Cs and move over to 2.4Ghz with a conversion module.
As far as the advantages of 2.4Ghz over xxMhz, Dirtybird pretty much nailed it
Just because your pin is always free at your flying field, does not always mean that your "channel" is free!!
Many of those old 72Mhz radios your buddies ditched can pop up at a school yard near your field. It's happened at our field
Pete
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Old 12-20-2013, 09:24 AM
  #34
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I fly using my Futabe 8U (PCM) more than my new Futaba 12.(2.4 Ghz). But that's because I don't plan to change out the gear in my old planes and the radio always works. In fact, my new 12 bugged out on my first flight of my Raptor and dumped it in from a low hover pretty hard.

I isolated the problem to the receiver and sent it in. They said they couldn't find anything wrong with it but sent me a new one anyway. Honestly, for an almost $1,000 radio, I already don't trust it. My 8U is still solid.
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Old 12-20-2013, 09:30 AM
  #35
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FRSKY has local dealers that stand behind their products. The one I have bought my radio from is Aloft Hobbies. On my radio one stick was a problem. It did not return to the same position every time. Aloft provided new sticks for both positions that are excellent. I did not even have to return the old sticks.
No matter what you think, the Chinese are making excellent products and stand behind them.
I had a RCGF engine that froze on the first run. The needle bearings on the crank came apart. . I contacted the factory and they directed me to a distributor He gave me a new motor .Its an excellent motor
I don't deal with HK too much but their covering is better than monocoat and it costs 1/2 monocoat.
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Old 12-20-2013, 09:43 AM
  #36
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Quote:
Originally Posted by Muttdog View Post
I disagree when it comes to FrSky. There stuff has pretty much been proven and there are very few failures that I am aware of. Everyone seems to love that new Taranis Tx they developed. That and the Turnigy 9X have some pretty loyal followers. Not only that but there are advantages with the open source software they use if you are a tinkerer. You are correct about product support and it is dismal but fortunately none of the FrSky products I purchased ever had a single issue. RC model Reviews did a great test on the FrSky frequency hopping protocol and it appears to be a very robust link. My only issue (and Tx related crash) was when I left it in range test mode for my flight. I saw it going in and out of fail safe mode until it lost all control. Realized about 5 seconds after it hit the ground what I did. DOH!
One of the advantages of Taranis or the 9x is you can contact the operating system designers and get an alarm set so it lets you know you are in range check mode. Try that with Futaba.
I think You could program it so it beeps when in that mode. Ask Scott.
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Old 12-20-2013, 09:47 AM
  #37
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2.4 GHz wavelength has much higher incurred losses then 72MHz wavelength.
Therefore, when it comes to range, the 100mW RF output on 2.4 GHz radio is no match
to a 750mW RF output on 72MHz radio. When out of range, error correction, unique GUID code,
and the "robust" digital pulse train will do no good.
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Old 12-20-2013, 10:53 AM
  #38
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Quote:
Originally Posted by Dave View Post
2.4 GHz wavelength has much higher incurred losses then 72MHz wavelength.
Therefore, when it comes to range, the 100mW RF output on 2.4 GHz radio is no match
to a 750mW RF output on 72MHz radio. When out of range, error correction, unique GUID code,
and the "robust" digital pulse train will do no good.
The truth be told however it falls on death ears.
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Old 12-20-2013, 11:24 AM
  #39
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Path loss is proportional to frequency squared. (2400 / 72)^2 = 1111. You would have to transmit 1111 times (yes, over one thousand times) more power at 2.4 GHz than you would at 72 MHz to create the same signal strength at the terminals of the receive antenna. This is not a dissipative loss; it is related to the physical versus electrical length of the antennas. It is a basic concept of antenna theory and there is no getting around it.

This difference is made up using spread spectrum processing gain, diversity reception (mutliple receive antennas), more sensitive receivers, and so on.

Anyway, sorry for the distraction. 2.4 GHz systems do work and work well. So do 72 MHz systems.

Last edited by JPMacG; 12-20-2013 at 11:26 AM.
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Old 12-20-2013, 11:37 AM
  #40
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Quote:
Originally Posted by Dave View Post
2.4 GHz wavelength has much higher incurred losses then 72MHz wavelength.
Therefore, when it comes to range, the 100mW RF output on 2.4 GHz radio is no match
to a 750mW RF output on 72MHz radio. When out of range, error correction, unique GUID code,
and the "robust" digital pulse train will do no good.
The receiver sensitivity of a 2.4 system is at least 6db better due to SS processor gain. Each 3db is the same as doubling the transmitter power. This means the 2.4 system is putting out 600 mw equivalent. If you do a link analysis you will find very little difference in the range capability of the two systems.
There are some chips advertized at -110db sensitivity. This would make the 2.4 system far better. i don't know it such chips have made it into our equipment though
PCM systems have some processor gain that will make it better but those systems suffer from high latency due to the low bandwidth available on 72.
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Old 12-20-2013, 11:50 AM
  #41
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Quote:
Originally Posted by JPMacG View Post
Path loss is proportional to frequency squared. (2400 / 72)^2 = 1111. You would have to transmit 1111 times (yes, over one thousand times) more power at 2.4 GHz than you would at 72 MHz to create the same signal strength at the terminals of the receive antenna. This is not a dissipative loss; it is related to the physical versus electrical length of the antennas. It is a basic concept of antenna theory and there is no getting around it.

This difference is made up using spread spectrum processing gain, diversity reception (mutliple receive antennas), more sensitive receivers, and so on.

Anyway, sorry for the distraction. 2.4 GHz systems do work and work well. So do 72 MHz systems.
Can you provide a reference for statement?
If true the 2.4 system processor gain would have to be at least 30db to even work at all.
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Old 12-20-2013, 12:34 PM
  #42
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Most any antenna engineering textbook covers this subject. Some examples are:

Antennas by John Kraus
Antenna Theory, Analysis and Design by Constatine Balanis
Electromagnetic Waves and Radiating Systems by Jordan
Antenna Theory and Design by Stutzman and Thiele
Antenna Engineering Handbook by John Volakis
Antenna Engineering Handbook by Johnson and Jasik

Also, Wikipedia has an article on path loss:
http://en.wikipedia.org/wiki/Path_loss

Although Wikipedia does not relate it to frequency in a direct manner. You would have to do some manipulation of their equations.

I'm at home and my library is at work, so I can't give specific page references. I will do it when I return to work on Jan 2 if you like.

Last edited by JPMacG; 12-20-2013 at 12:39 PM.
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Old 12-20-2013, 12:50 PM
  #43
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Quote:
Originally Posted by dirtybird View Post
Can you provide a reference for statement?
If true the 2.4 system processor gain would have to be at least 30db to even work at all.
Processor gain certainly helps, but I think there is more to it than processor gain. Atmospheric and man-made noise is lower at 2.4 than at 72, so the receiver can operate at lower signal levels. The diversity receive antennas help a lot I suspect. 2.4 GHz receiver sensitivities may be better. And the 2.4 GHz antennas are probably better matched than the 72 MHz antennas we use where one side of the antenna is made up of the transmitter case or the cables inside the airplane.
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Old 12-20-2013, 01:04 PM
  #44
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Good discussion, but off topic...
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Old 12-20-2013, 01:19 PM
  #45
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Excuse me, it is not off topic. It is entirely germane to the topic. Go back and read the OPs first post.
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Old 12-20-2013, 01:48 PM
  #46
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Hi Guy, I'm using a futaba 9c and an 8u, both upgraded to2.4 using the hitec conversion, works great, unbelievable range,
and all receivers all come with receiver battery telemetry,standard! If the planes rx battery gets low the transmitter modular beeps warning you. I am also using eneloop 2000ma transmitter batteries,from Batteries America, last up to 8 hours,and still have 9.8 volts.If you end up having allot of planes like me, 25 get the 64k chip from Hansen hobbies$36 and you will have 32 models in your 9c futaba radio. Love it, thanks Ed
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Old 12-20-2013, 02:48 PM
  #47
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9 Cap beeats almost all radios out there and if U want to go 2.4 U can buy a module from HiTec or Futaba and God forbid from JR or Spectrum and then U have the Best of all worlds. Don't give up on your 9 CAP it a better radio than 90% of the cheep spectrum junk out there and 2.4 is only the RF the programing is what's important not the RF except when it comes to the spectrum Brand as a brand then be ware ... U've got a large investment in your old receivers and such go with a module. I personally went with the HiTec RCD 2.4 module and 2 9 channel receivers for around $200 then Because I wanted to check out the Telemetry stuff offered I later purchaced an Aroura 9 system then 2 because I found one used on RCU cheep $175 with an extra module and receiver.. Good luck with what ever U do but U'll probably never find anyone on your Frequency Just remember to take the PIN.
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Old 12-20-2013, 03:07 PM
  #48
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I have two 9 Caps. One with a Futaba TM-8 module FASST 2.4 conversion and the other on steel antenna 72 using PCM recievers. Have had wonderful reliability & performance from both. Welcome back to this super fun world of RC.
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Old 12-20-2013, 03:09 PM
  #49
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I have several 2.4 Futaba transmitters and several of their receivers and several FrSky receivers. They work great, never a hit or glitch. I can't say that with some of the older FM stuff I have used. I was told that we were secondary users on the FM band. That there were 4 mobile ground channels available between each of our FM channels. Maybe that has something to do with it. I don't know. I just know I switched over and I have never had a hit since.
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Old 12-20-2013, 03:22 PM
  #50
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You are correct. I went to
http://www.siversima.com/rf-calculat...ss-calculator/
for 1 km the path loss for 72mhz is 69.2
for 1km at 2.4ghz its 100.5 db. A difference of 30db
I had heard the you could get 40DB processor gain but I thought it was optimistic.
It must be so or they wouldn't work at all.
The XPS receivers I have are 1/4 wave just like the old 72.
There is plenty of noise on 2.4ghz.
I spent a year checking out the ground receivers for Lunar Orbitor. (3.0ghz)
There was a 30 db difference between pointing the antenna at the horizon or Zenith.
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