Norcim rc electronics club page 5……

This page is dedicated to the late Dave McQue. Senior Radio Electronics Engineer at the Bletchley Park code breaking establishment during the Second World War. Dave’s interest in Model Radio control spanned his lifetime. He contributed to the specifications of R/C transmitters for use on the 35MHz FM band and added to BMFA discussions on receiver testing.

We are aware that the following listed receiver notes are now well out of date (new receivers not listed) but they are recorded for the method that was used by Dave McQue to arrive at the results.

Another norcim web page covering some intriguing test data of many commercial radio control receivers. If you are into technical facts and figures of R/C systems, then this page begins to show just how ‘technically good’ various makes of receivers are. The following test data investigates probably the most important quality of a model radio control receiver, that of ‘sensitivity’. This determines how far away the receiver can operate a model without loss of the radio link.

IN THE DISTANT PAST! When micron sold radio control kits for a living, samples of the kits used to be tested and compared with commercially available units of the day. One of the primary tests, involved comparing the range of different units, which in turn gave a degree of satisfaction when the kit samples were up there with the best at that time! As there was a field at the rear of the workshop, range testing was very practical. With a nicad, receiver and servo in a plastic box, the number of paces away from the Tx (antenna collapsed) before servo ‘noise’ from the box could be heard. (non visible jitter) This was noted. Then a further number of paces were taken to loose transmitter control altogether, this was also noted. These tests were ongoing as new circuitry was tried and new commercial equipment became available to compare. All our kits were PPM type so little notice was given to the PCM equipment that was evolving. Looking back, this kind of testing invariably took place on hot summer days with little wind! I wonder why? (said he, carrying a model and can of fuel!).

RADIO CONTROL RECEIVER TESTING DATA  D. McQue

Purpose :- To measure the various receivers’ sensitivity using a Signal generator and dummy antenna.

Apparatus :-

Panasonic Signal Generator VP819A modulated by the “Buddy Box’’ output from a Futaba T8UPS with its RF output switched off. Or JR X-3810 for JR PCM RX tests.

Regulated Power supply set to 5 Volts.  500 mA analogue meter.

Dummy antenna to terminate the 50-Ohm cable from the Signal generator and simulate a 1m-model antenna. Made from a 47R Ohm resistor in series with a 3.9-Ohm resistor. The output taken from the junction, via a 4.7 pf capacitor to the RX ant input with its wire antenna disconnected. (as shown in Fig 7a)

A Hitec HS-615 servo was plugged into the Aileron Channel.

Results :-

Note the signal level for control is where servo twitching is just apparent for PPM receivers. At this point there is a large servo current draw of more than 250mA.

Abbreviations :-  SC = Single Conversion, DC= Dual Conversion.  PPM=Pulse Position Modulation, PCM=Pulse Code Modulation

MAKE/MODEL OF RECEIVER	CONVERSION TYPE	MODULATION TYPE	MIN SIGNAL LEVEL FOR <20 MA SERVO CURRENT (uV)	MIN SIGNAL LEVEL FOR CONTROL OF SERVOS (uV)
DALASY
MINI/NANO	SC	PPM	350	35
FUTABA
FP-R138DF	DC	PPM	79	7.9
R149DP	DC	PCM	2.5	2.5
R116IIP	SC	PCM	2.5	2.5
GWS
GWRD-8	DC	PPM	350	35
HITEC
FEATHER	SC	PPM	350	35
HFS-04 MG	SC	PPM	50	2.5
ELECTRON 6	DC	PPM	20	2 *
JETI
REX4 PLUS	SC	PPM	28	3.5 **
REX5	SC	PPM	35	5 **
JR
NER-326X	SC	PPM	55	10
NER-D940S	DC	PCM	1.8	1.8
MICRON
FET-7	DC	PPM	176	17.6
MINI-3371	SC	PPM	45	4.5
STD-3361	SC	PPM	176	17.6
FET-7 DSP	DC	PPM	14	7
MULTIPLEX
MINI DS-IPD	DC	PPM	8.8	2.8
P SUNG
SR4F	SC	PPM	700	88
SANWA
RX515	SC	PPM	8.85	1.24
RX611	SC	PPM	27.9	3.9
ACT	DC	PPM	442	44.2
SHULTZE
ALPHA 840S	SC	PPM	28	2.8
WEBRA
NANO S6 (1)	SC	PPM	620	62 (SAMPLE 1)
NANO S6 (2)	SC	PPM	350	35 (SAMPLE 2)

Notes Re above table:- *Electron 6 receiver DC Xtals are 10.7 MHz higher than chan freq. **These Jeti receivers are fitted with half size 50 cm Antennas.

COMMENTS :- (McQue).

Of interest is the lack of servo ‘Noise’ current for the PCM sets where the servo only drew current when it was commanded to move. In the case of PPM sets, the signal had to be as much as 20 dB stronger than that where servo twitching could be seen for the idle servo current, due to noise, to be less than 20 milliamps.

The Sanwa RX515 is the most sensitive receiver while the Multiplex and Shultze are the next most sensitive PPM Rx. Their signal processing provides considerable reduction of the servo ‘Noise’ current on weak signals in the range below 8.8uV for the Multiplex and 28uV for the Shultze. Whereas, they are completely eliminated with all the PCM receivers.

GWS admitted that the RD8 antenna matching was set for the 72 MHz band.

The local model shop gave the P Sung SRF/35 to me as nobody wanted it.

Webra claim 2 uV sensitivity for the Nano S6 so I must have bought a poor sample. (sample 1) Note the improved result shown was after careful re-tuning.

Al’s Hobbies provided later versions of the Webra nano S6 (Webra sample 2) and the Dalasy mini/nano for test.

While the performance of the average PPM system has proved adequate for most users, those with more demanding requirements will be satisfied with nothing less than Dual Conversion PCM gear.

Micron’s New FET-7 DSP Receiver Except for the slowing of servo response on weak signals it is the best of the processed PPM I have come across so far. Being able to set fail-safe positions in the air is another useful novelty.

Update D. McQue

THE ABOVE RECEIVER SENSITIVITY TESTS by Dave McQue are real interesting for the following reasons:-

They show that:

(1)There are huge differences in receiver sensitivity values of recognised commercial R/C receivers. (some receivers are over thirty times more sensitive!) All of these receivers sell by the thousand and are obviously completely suitable for model control. Till now, most R/C manufacturers have quoted receiver sensitivity values of around 2 to 3 microvolts.

(2)Dual Conversion PPM receivers appear to give little advantage (simply in terms of sensitivity!).

(3)Some PPM receivers have advanced decoder processing that ‘smoothes out’ servo jitter at range. (this is a definite technical advantage for PPM receivers) (but see note (7). (see also footnote).

(4) PCM receivers will work without servo jitter, with a transmitter signal up to ten times weaker! than a PPM receiver.

(5)Servos of PPM systems could be consuming up to a quarter of an amp per servo during severe jitter at extreme range or during sudden mild interference, (this could exhaust the receiver battery quickly, with catastrophic results).

(6)If you’re into long duration flying, then your receiver battery will last much longer between charges using a PCM system.

(7)Because of the inherent servo ‘jitter’ before complete loss of range with a PPM system, it could be argued that this will ‘warn’ the pilot before complete loss of signal. (Experienced pilots would bring the model closer to the Tx).

(8)There is no warning of range loss with a PCM system. (Say with sudden mild interference). Edge of range condition occurs immediately and if the model is moving away from the transmitter, it is unlikely that the radio link with the transmitter would be restored.

WITH R/C TRANSMITTER output power, now controlled by ‘Type Approval’, the maximum range of an R/C system is completely dependant upon the receiver sensitivity. For large model aircraft use in particular, a receiver with good sensitivity is imperative. (Other qualities of a ‘good’ receiver include, rejection of other R/C transmitters, rejection of strong out of band transmissions, performance with electric motors, temperature stability, vibration, size, weight, cost etc.)

FOOTNOTE RE: NOTE (3) ABOVE. Servo jitter occurs at range, with all PPM receivers. Often well before maximum range is reached. The data shows that the signal strength needed to ‘just’ prevent servo jitter is normally 10 times the signal strength of that at the end of range. (a ‘signal ratio’ of 10 to 1).

SOME PPM RECEIVERS however, use better decoding processing circuitry. This allows a much greater receiver range before servo jitter begins. Such receivers may only need, say 5 times the ‘edge of range’ signal strength, to keep the servos quiet. This is a technical advantage for a PPM receiver, as battery consumption is greatly reduced under extreme range and/or interference conditions. (a ‘signal ratio’ of 5 to 1).

THE SIGNAL RATIO is the uV value in the yellow column divided by the uV value in the red column. The lower this ratio is, then the better the PPM receiver decoder processing is. (giving lower battery consumption under extreme conditions).

The Micron FET-7 DSP now has the best signal decoding of all the PPM receivers tested to date with a signal ratio of 2 to 1 which best approaches that of PCM type performance.

The Multiplex Mini DS-IPD is the next best decoding of all the PPM receivers tested, with a signal ratio of 3 to 1 and also approaches PCM type performance. The JR NER-326X follows with a ratio of just over 5 to 1. The Jeti REX5 and Sanwa RX515 are close behind.

NOTE THAT ALL PCM receivers give the maximum ‘signal ratio’ of 1 to 1 and as such, do not compromise battery consumption under any extreme condition.

Thanks for reading!