XJet

(also posted to RC Radios - Receivers - Servos )

Today I compared the sensitivity of three RC receivers: The Hitec RCD3500, the Hitec 555, the FMA M5

In each case, the receiver was attached to a freshly charged 600mA 4.8V receiver pack and a single non-digital servo.

It was mounted 30 inches above the ground and the antena wire was run horizontally (at right angles to the direction of the test transmitter) for 2/3 its length, then vertically for 1/3 its length.

The transmitter was a Hitec Eclipse with Spectra module.

All receivers were on Channel 23 (72.250MHz).

During the testing, the transmitter voltage remained between 9.6V and 9.8V and the antenna was kept fully collapsed. The transmitter was also kept at the same height above the ground and at the same orientation to the receiver throughout the testing.

The tests were conducted at a distance of more than 200 yards from any structure, underground or overhead wiring or other factors likely to influence the results.

Here's how they stacked up:

Hitec RCD3500: max range - 101 yards
Hitec 555: max range - 94 yards
FMA M5: max range - 65 yards

Notes:

The servo response degraded gradually with both Hitec receivers as they approached the limits of their operating range. Significant servo twitching was noted some 10-15 yards before all control was lost.

The FMA M5 stopped abruptly at the limit of its operating range with no twitching. A small amount of slugishness was noticed 5-6 yards before all control was lost.

Summary:

The FMA M5 has "S.M.A.R.T" decoding designed to reject corrupt data frames and this facility clearly works as advertised when the signal level drops to the point where noise impinges on the received signal.

However, I was disappointed that the FMA M5 has only 65% of the range offered by the Hitec receivers.

I was contemplating using the M5 in a large model but now I'm not too sure. Certainly it's a huge advance on the "park flyer" single-conversion receivers and their limited range and given it's ultra-light weight and small size would make a great alternative to these.

I have subsiquently flown the FMA M5 and noticed no problems, albeit this was in a small plane that ventured no more than 200 yards from the transmitter with its antenna fully extended.

The next round of testing involves subjecting all three receivers to burts of impulse noise, off-band signals and frequencies designed to produce 2IM and 3IM products.

BMatthews

This will be an interesting test. Thanks very much for sharing. It's not often we can see real world, real people results like this in direct comparison.

Andrew

Thanks for your efforts -- it is always nice to get personal experiences as compared to advertising hype.

I can understand implementing S.M.A.R.T. decoding for corrupt frame rejection with the FMA, but stopping with no twitching does not seem too advantageous to me. I would rather have glitching before losing signal rather than an abrupt loss -- at least with glitching, I would have some indication that something is amiss and have an opportunity to reduce the distance and get back on the ground (in a large piece [8D]).

the "other" Andrew

jboy381-RCU

have you tried it with the antenna all the way out???i wonder what would happen then???i don't know anyone that's flys with the antenna closed...

john

XJet

Unfortunately, testing over the ranges required with the antenna fully extended is problematic -- two-way radios or some other form of communication is required to relay the information between each end (and these transmitters may affect the results somewhat).

It's not so much the absolute range achieved with the antenna down which is important as the relative ranges.

In these tests it's pretty obvious that the FMA M5 has just 65% the sensitivity of the Hitec receivers. It would be reasonable to assume that the range with the transmitter antenna fully extended would still find the FMA-M5 having just 65% the range of the others.

In reality this likely means that the FMA may only have a range of mile 1,100 yards while the Hitec units work out to a mile or more. In practical terms the difference is academic, since it's pretty damned hard to see an average sized model at over 1,000 yards anyway.

However, the extra range offered by the Hitec units does provide a good amount of headroom when it comes to the dramatic changes in signal strength that accompany a model's constantly varying distance and orientation to the transmitter.

MarkD

I wonder if what you're seeing is the result of the FMA's M5 front end sensitivity, or an artifact of the SMART system?

If you take a radio with a "squelch" function ( like some Ham radios and CB's) the reciever still "hears" the signal, but no audio is output unless the received signal exceeds the squelch level. Maybe that is what is going on- the M5 has a "high" squelch setting because of the SMART system. The signal is still there and still strong enough to control the servos, but the SMART system's threshold is set tight.

Also, I wonder if ground relections are coming into play. Maybe the SMART system is hyper sensitive to out of phase signals and going into lockdown.

Several M5's and Extereme 5's are in use here, with the antenns bent into a "U" shape inside the right wing panels. They have been flown to slant ranges of at least 1500 feet without a glitch.

This is very interresting- thanks for taking the time and effort to try this XJet!

Mark D

XJet

There did appear to be a degree of hysteresis with the M5's decoder -- ie: during testing, once the servo stopped responding, the transmitter had to be moved several yards closer to the receiver before it would start working again. At that stage the distance could be increased by several paces again until it tripped into failsafe mode.

This was not unexpected and is a reasonable way to handle the situation.

I would say that 1,500 feet of range is well within the capabilities of the M5 -- I *estimate* that when used with a typical RC transmitter it probably has a range of at least 2,500 feet which should be more than adequate for any model airplane use (and three or four times that offered by similarly sized Park-Flyer single-conversion receivers).

John C

This is still good information for us that fly sailplanes. I have an M5 in a small Kelly and Hitec 555s in larger planes. I have had all of them go out of sight on me, and recovered by spinning them down until regaining visual contact.

That said, I'll not put the F5 in a large sailplane where the range capability could be problematic