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Home✈️Aircraft🚁HelicopterHelicopter Main Discussion › Transmitter Power Output
06-02-2016 11:03 AM  4 years ago
rcnut

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Rockford, Illinois

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What about the Jeti radios?Team Miniature Aircraft
"I love the smell of Nitro in the morning!"
...Citizen 654!
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06-02-2016 11:35 AM  4 years ago
Heli_Splatter

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USA

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Interpreting Results.
I would respectfully advise anyone following this thread that the results are based on a rather inexpensive device (<$200).

The results are biased in that any individual radio might not be tuned properly and performing to max specification due to any number of factors. I would not base a purchasing decision on what is found here in this thread. I am sure the OP has every good intention and I like what he has done.

Though we will probably never see it; a group like consumers reports with a fantastic electronics lab could do a proper comparison.

Full disclosure would have me say that I own and use JR and Spektrum radios. I know that other brands are of equal (or better?) quality and think brand choice is a personal preference.

No matter what your choice, read and learn how to use your system properly. It is more than turning the switch on.
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06-02-2016 02:01 PM  4 years ago
Four Stroker

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Atlanta

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Yes indeed. This thread is about maintenance and NOT design. The cheap spectrum analyzer is perfectly valid +/- 3 dB or so. Note that there are huge differences within the same brand and type.

As I said, I attribute the low output to aging of the chips or fiddling with the antennas.

IF you want to know how much power your transmitter puts out NEW,
go to the FCC website and put in the number on the back of your radio in the first two boxes:

https://apps.fcc.gov/oetcf/eas/repo...nericSearch.cfm

and read the report.

Note that twice the power is 3 dB and does not matter at all in a link budget. Even 10 dB is probably not important unless you fly a long long way off. Phil Kraft pointed out long ago that you need 40 dB margin to account for pointing the transmitter antenna at an airplane flying away so that it's antenna was pointing at you.

My point is that transmitters with very low power are flying all over the place and the average modeler has no way of knowing. I think every club should have one of these cheap spectrum analyzers and check everyone's transmitter once in a while. I ain't got it ! is still valid sometimes.

The differences in power output for a NEW transmitter is NOT any reason at all to pick a brand. They are all about the same.
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06-02-2016 04:08 PM  4 years ago
AirWolfRC

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FYI,
The 2.4 - 2.4835 GHz is part of the ISM band (Industrial, Scientific and Medical) and where we operate. This is also where WiFi, Bluetooth, cordless phones and microwave ovens operate.

In the USA, it is limited to 1000 miliwatts (30db) output power. In Europe it is limited to 10 miliwatts (10db). (0dbm = 1 miliwatt, 10dbm = 10 miliwatt)

The back channel operations (video, RPM, engine temp and other telemetry) will use a lot less power for practical reasons more than regulatory reasons.

And all this is digital and I question how good a low cost spectrum analyzer is at quantifying a fast moving digital signal.

I will say that it is useful when relatively comparing multiple transmitters.
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06-02-2016 04:11 PM  4 years ago
Four Stroker

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Atlanta

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Frequency hopping Futaba, DSMX, etc. can use 100 mW in the EU and Japan. I know of no 10 mW radios sold in the EU.

Edit: The proposed update in 2015 allowed for 100 mW only if you "listen before you talk". Otherwise it was 10 mW. There may be some systems limited to 10 mW because they don't listen.
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06-02-2016 04:15 PM  4 years ago
AirWolfRC

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You may want to read this over,
http://www.ti.com/lit/an/swra048/swra048.pdf

and if that's not confusing enough,
http://www.itu.int/en/ITU-R/study-g...20of%20SRDs.pdf
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06-02-2016 04:17 PM  4 years ago
Four Stroker

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Atlanta

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Do you have a link to the actual 2015 EU regulations ? I don't know how RC manufacturers comply. I believe DMSS and FASSTest comply by listening before they talk but I don't have any info. on this.
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06-02-2016 04:27 PM  4 years ago
AirWolfRC

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The common line in the regulations here is "must tolerate interference".
Nothing about "listen before transmitting".

Spektrum does the "listen before transmit" when selecting a frequency pair to operate on at power up.
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06-02-2016 04:36 PM  4 years ago
Four Stroker

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Atlanta

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Too much for me to read at ETSI. I haven't looked into this in a couple of years when I worked for a company that was going to market world wide.

Looks like 10 mW for practically anything. This would be fine if the hopping was good. I don't see any mention of the "listen before you talk". This may have been thrown out of the proposal.

Are you suggesting that some of these transmitters were designed for EU and that accounts for the low power ? Could be true ?

And also when if ever are these harmonized rules going into effect ?

BUT some of these modules were built 10 years or more ago before any of these new rules were considered and appear in the FCC with ~50 mW which they don't seem to have anymore.
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06-02-2016 04:52 PM  4 years ago
Four Stroker

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06-02-2016 04:54 PM  4 years ago
teamdavey2001

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My understanding of the Euro regs is that 100 mw is OK if you do lbt OR have media utilization factor less than some value.
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06-02-2016 06:38 PM  4 years ago
Four Stroker

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TeamDavey does this stuff for a living.

We are getting off track. TeamDavey how do you account for the great variations among the same brand and protocol ? i.e. Futaba FASST goes from -35 dB to -52 dB ? That is a power factor of 50 !
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06-02-2016 07:37 PM  4 years ago
teamdavey2001

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well - I am semi retired, and this stuff is more of an (interesting) sideline to what I really get paid to do, but anyway....

I wish I could give a clear answer but....

Based on some field strength "sniffing" at the field I have seen quite wide variations between txs from the same brand and between brands. I can't equate those "sniffs" quantitatively to your dB measurements for obvious reasons, but they do confirm that large variations seem to exist. I would love to get a representative sample to do more engineering testing.

Among the collection of Txs I own - all Spektrum/JR with one Orange module for fun I see little variation in dB terms when measured at constant distance using another "cheap spectrum analyser". Note that all of the Spektrum/JR radios are single antenna early RF modules - I do not have any of the later FCC ID units or any of the dual antenna types to play with at home.

I'll try to get some better data if I can talk friends into putting up with me making the measurements

One thing is for sure - there is a lot of margin in most systems today, so the average user may never know that his Tx is "limp".
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06-02-2016 08:01 PM  4 years ago
Four Stroker

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I believe it was you ? and I who both measured the range test mode of Futaba at 23 dB down. The guy had a real Agilent spectrum analyzer. I have seen guys take off happy as hell if they got 100 feet - in range test mode. Now the worst of my test bunch can't be more than 6 dB above that. One guy crashed several weeks in a row. We range tested his Spektrum and got about 100 feet. We full power tested his Spektrum and got 100 feet. Range test mode is not reliable.
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06-02-2016 08:16 PM  4 years ago
teamdavey2001

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Spektrum has semi-officially admitted that range test mode is not a 100% test since it does not rely on the PA working.

There are those of us who use a microwave leakage tester as a go/no go test for transmitters since there is no other way of knowing that the PA and antenna a actually doing anything!

It wasn't me that measured the range test mode on a Futaba. I have on Spektrum and it's a reduction of 30 dB - actually a bit over on my measurement but likely intended to be 30. Again that is on older hardware.
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06-02-2016 08:18 PM  4 years ago
Four Stroker

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The JR DMSS is 35 dB down in range test mode.
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06-02-2016 09:35 PM  4 years ago
teamdavey2001

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Thanks - I'll add that to my mental data base.

Regards
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06-09-2016 01:51 PM  4 years ago
Four Stroker

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Atlanta

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Tested an original Spectrum module with the wire running up to the antenna Wed. It was down 30 dB from a new DX8. Pilot was not concerned. Wiggling the antenna changed the output by 10's of dB.

My conclusion is that manufacturers should put fixed antennas OR internal antennas (Futaba 10J) OR patch antennas (German Graupner) on our transmitters. If I had a transmitter with a replaceable antenna like the 28X, I would replace it once a year !

I am out of here.
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06-09-2016 02:23 PM  4 years ago
icanfly

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ontario

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I read the max legal ma output in the west is 100ma while the JR and DX7 should put out 120ma (dx7 does),

I have a DX7 and an AR7200bx with sat on my nitro Shuttle, did a paces measurement of signal and went 60 paces before the signal cut, that was twice the distance of a single 6100 with two antenna. The AR7200bx and sat antenna wires are positioned 90/90/90 with the two 7200 wires 90° and the sat 90° to them.

Yeah manufacurers been weakening the output progressively hoping more people would crash and contribute to the economy with new parts/helis orders because it's a big conspiracy to keep cash registers, c-card charges flowing in the name of stock market margins and tax, bankers pulling all the strings so they can stay fat like swine to the slaughter and/or boost their ego among their peers, the world is one big conspiracy to evade truth and right in the sight of gawd, lol.

Higher - db means less signal? probably. What was the estimated per foot range of the first line tx's? the jr and dx7 (designed by jr). What about Jeti and frsky?

You could reason that with a dsm2 signal there should be more power to make sure of a strong uninterrupted signal whereas dsmx may not need much power to do it's job safely and accurately within los.

Ever see the vid of a guy flying a quad for 25 minutes out of los maybe about 10mi from his position with a reflector on his antenna? English guy.

Reading about that "listen before you talk" aspect it would prove how many guys have not maximized the antennas on their helis rx's for maximum reception, while cf, lipo, motor proximity/blocking reduces signal by nothing advertised. There is where rx/sat positioning can make the difference in reception, but no one reads up until it's too late and they end up asking what happened while paying the price of just plain ignorance, placing rx antennas in all the wrong places on the heli. That guy in SA who flew a Goby700 into hydro wires a year and a half ago had only one sat as rx, lesson learned as he got schooled hard core $ with $2k reduced to ashes in a matter of minutes, smart guys.
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06-10-2016 03:02 AM  4 years ago
Gearhead

rrMaster

Vt

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if this helps tell you how well these things work,

some 6 or 7 years ago (at the field) I was flying my 63" plane on my 9303, PCM of course, well the plane was out some 300 feet, I figure a foot ball field away, I started into my turn when I hear from behind me "hey Jim, you going-na pull out your antenna",,, me "oooops"

I Emailed Horizon and told them about it, I was boasting , and my reply back to me said "you were lucky",, never the less I was lucky, but I did the same thing a 2nd time a couple weeks later,,,,,, oooops
Jim
Buzz Buzz Buzz
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