FMA Direct : FAQs

FAQS | RECEIVERS

Are there software upgrades for FS Receivers?

Flight System receivers began shipping June 20, 2003 as the FS5. The first software version for the FS5 was V1.28. You can verify the software version that you have by looking on the cover of your manual. The manual version numbers correlate to the software version in your unit. From the direct results of customer feedback and further testing by FMA Direct, there will be continued improvements to software and/or hardware as time progresses. FMA Direct will offer continued support for product in the field in the form of free software upgrades and new manuals to any customer who sees a need to upgrade. We will not be able to upgrade hardware and the software updates that will be available may or may not apply to future hardware plans. Any software and/or hardware changes that are made will be catalogued below. Should you elect to upgrade your software, simply indicate this in a note and return the unit to customer service postage paid. FMA Direct will charge the normal shipping and handling fee of $8.00 to return the reprogrammed devices and include a free manual that corresponds to your new software version.

Is the range of the FS8 Receiver on 50Mhz slightly less than on 72Mhz? Is there something that can be done to improve the range?

The range is shortened somewhat on any 50 MHz receiver. It's not easy to establish how much shorter. It depends on several factors including transmitter output, length of the transmitter antenna, etc. All other things equal, the range reduction can be contributed entirely to antenna length. The 1/4 wavelength of a 72 MHz antenna is around 40". The 1/4 wavelength of a 50 MHz antenna is close to 5 ft. Of course, it is not practical to use a 5 ft long antenna on the TX or RX. So in R/C it isn't practical to take advantage of the full range capability of the electronics. If one were to attach 5 ft long antennas to the TX and/or RX, the range would be greater than 72 MHz due to increase antenna capture. But some of the range reduction at 50 MHz is made up for by the fact that transistor amplifiers are more efficient at lower frequencies. By design, all other things equal, 50 MHz TX should have higher power output and RX should be slightly more sensitive.

But even with range reduction, there is still great margin built into these systems. Ground range checks with TX antenna collapsed will be visibly noticable to a customer. But once the antenna on the TX is extended, one can still fly a model airplane further than visible range without loss of signal. When we test FMA equipment, we collapse the antenna on the TX and fly the airplane out until it is a tiny spec in the sky. Even in these tests, which equate to about 1/10 power output on the TX, we do not experience any visible loss of control. Part of this comes from the fact that line of sight ground range is usually at least tripled when the aircraft is aloft.

The only time customers will experience real range issues with an FMA receiver is if his transmitter is off frequency by more than +/- 1 KHz. In this case, if customer returns the RX with his TX, we will align the transmitter for no charge except return shipping. This is a service we provide to support our sales efforts.

What's different about the V 1.29 code for FS5?

V1.29 Code began shipping on 09/30/03. This code includes the following changes from V1.28 and is available to all customers with hardware shipped since 06/20/03:

1) Raised the startup delay timer. This should fix the "EEPROM READ FAIL ONE TIME" error on the viewer

2) Removed servo centering in setup mode to and made the servo always track the stick position. This prevents certain ESC's from arming in setup mode which may cause the propeller to turn in setup mode on electric aircraft.

3) Lowered FS Programming stick movement threshold from 12 to 6 - this allows low rate programmed channels to enter failsafe programming mode.

4) Lowered TX Startup frames from 25 to 20 frames. This allows quicker startup.

5) Raised the FS Setup Factory Reset button hold time from 3 to 10 seconds. You have to hold the button down 10 sec. to reset all channels to "last frame hold"

Can I cut the antenna length down on my receiver?

Yes. As spelled out in many of the FMA Direct receiver operations manuals, you can cut the antenna length down successfully without de-tuning the receiver. Be aware that your range will be reduced. The best technique is to cut off small pieces and range test to make sure you have enough range for your requirements.

Can I use a base loaded antenna on an Extreme 5 receiver. I have 2 of them and they are great but the antenna is too long for some of my slow flyers.

The antenna on any FMA receiver can be cut to as short as half-length without retuning the receiver because FMA uses a 50 ohm impedance match in all receivers. The reduction in range will be the same as if you used a base loaded antenna. For example, whether you use a base loaded that is 18 inches, or cut the antenna to 18 inches, you lose 1/2=3 db of sensitivity. This means the margin needed for solid operation is reduced by 3 db; however, since the margin is as much as 30 db at normal flying range, this has no impact. The base loaded is the only way you can shorten the antennna on other manufacturers receivers because the base load attempts to give a match with the unknowwn impedance of the front end so the receiver does not detune. Cut the FMA antenna down to as short as 18 inches; but do be sure to do a range check. There should be a good match with range and the distance you can see the small model. That is, you should have a ground range at least equal to the distance you could see to fly the model. That means that air range will be about 1 1/2 times the max ground range. When FMA qualifies a new receiver design, as a matter of practice, we fly it in a six-foot span Senior Falcon to the max altitude that eagle-eye Howard Matos can see it. This is way beyond what most of us can see the airplane. We then collapse the transmitter antenna and fly as you normally would fly.

Will your receivers operate with my Futaba 9ZS or other Futaba synthesized transmitter?

Currently, the only receivers we manufacture that is compatible with the Futaba synthesized equipment is our Fortress series receivers (201FM72 and 202FM72). For an explanation, please read the following:

1) Frequency synthesis is the method whereby a transmitter can be "programmed" to work on any R/C channel; not just one like normal transmitters.

2) With some synthesized systems, the circuit that "locks" on to a frequency does not, by nature, like to change frequencies.

3) When you have FM type transmitters, the very nature of FM modulation means the frequency is constantly shifting back and forth.

4) A PCM system will spend equal amounts of time above and below the center frequency when it is modulating.

5) A PPM system (normal FM like our receivers), spends half as much time above the center frequency as it does below.

6) If the synthesized circuitry for Futaba transmitters is modulated by PCM it will run on frequency. If it then receives PPM data, it might not run on frequency.

7) Our understanding of the technical issues regarding the Futaba synthesized transmitters leads us to believe that Futaba modified the standard PPM modulation scheme defined in the late 60's so that it would spend equal amounts of time above and below center frequency.

8) When the output from these transmitters is fed into a normal PPM receiver, the receiver cannot properly "decode" the altered signal unless either extra componentry is added, or the normal PPM receiver circuitry is fine-tuned to work with the Futaba synthesized output.

If a fixed frequency module is installed into the Futaba transmitters, it outputs normal PPM data and will work with all of our receivers. In our attempts to satisfy the market with smaller and smaller equipment, we have felt it is not beneficial to design our equipment to work with this peculiar transmitter. The FMA Fortress series receivers do operate normally with the Futaba synthesized transmitters, but they are larger and more costly to manufacture.

Will FMA receiver(s) work with my o.e.m. transmitter?

With rare exceptions, FMA Direct receivers are available to be compatible with any transmitter manufactured over the past 25 or so years. The specific exceptions are one each model transmitter manufactured by Futaba, Airtronics, and JR when they first introduced the so-called PCM encoding format in the early 1980s. Those three transmitters can not be switched to PPM. You must confirm that your PCM transmitter has the capability to be switched or programmed for PPM encoding. The FMA Model 202AM is about the only AM receiver available on airplane frequencies. The FCC requires transmitters at 72 MHz and 75 MHz to be within approximately 1500 Hz of the specified frequency. We often find brand new transmitters that are off by 1500 Hz or more. The original equipment receiver works with that transmitter, although not in optimum fashion. However, it generally works because it is has a relatively broad band pass and doesn’t see the difference in frequency. Of course, that means it is more susceptible to adjacent channel interference, particularly if the adjacent channel transmitter is off frequency in the direction of your receiver. FMA receivers have very narrow band pass to reduce the susceptibility to adjacent channel interference. If interfaced with a transmitter that is off by 1000 or more Hz, the FMA receiver may reject the transmitter. We offer a service to check the tuning of your transmitter if you bought our receiver and it will not listen to your transmitter. Don’t worry, if you instruct FMA Technicians to re-tune your transmitter, it will still work with your existing equipment.

Why does FMA Have So Many Receivers?

We try to meet the specialized needs of our consumers up to a point. Some look for the lightest, smallest receiver, so we did the 6 and 8 channel Quantum without the added circuitry, space, and weight imposed by automatic shift. You have to specify which type you need and it can not readily be changed. The Magnum is 6 or 8 channels and has automatic shift so you can use it with either type transmitter without concern for the shift. They are larger and about 3 grams heavier than Quantum. In recognition that few slow/park flyers or hand-launch gliders need more than 5 channels, we did the Extreme 5. We had just completed the design of our IR system at that time and that produced an excellent, tiny decoder based on a PIC chip, so that was incorporated to give you the smallest, lightest dual conversion receiver available. It adds the bonus of having the microprocessor decoder check each frame and hold off any bad frame so you can fly through a glitch and never know it. We do continue to carry the Fortress 2000 as there are many customers who want a plastic case and who like to have all eight channels available without having to use a Y-block for battery. The durable fortress micro is stocked for use in the RAZOR and also is the only receiver available from anyone as AM at 72 MHz.

What is PPM?

PPM stands for Pulse Position Modulation and is a term describing the concept for encoding using the scheme that came into being in the early 1960’s. The concept is the encoding scheme itself; not to be confused with modulation. The only form of modulation permitted for R/C systems in those days was Amplitude Modulation (AM). PPM in communications is based on taking a signal (Voice, music, et al) and operating on the continuously variable analog signal at sampling intervals with a voltage-to-pulse generator. The higher the amplitude of the signal, the closer the pulses are together and the higher the frequency of that variation, the faster the variations in pulse position occur. At the receiving end, whether by wire or radio, you can pass the pulse train through an integrator and reconstitute the original analog wave. The R/C decoder, instead, sorts out the variation from one pulse to the next in a very specific frame of pulses. It then converts a serial stream of data pulses into parallel servo output control pulses to drive the individual servos connected. The specifications of these pulses that have come to be pretty well standardized at 1.5 ms with the control position carried in continuous variation of the decoded pulse width by + and - 0.5 ms, maximum.

What is PCM?

PCM stands for Pulse Code Modulation. PCM in R/C is actually no closer to an accurate description than PPM! PCM is another encoding scheme, not a modulation scheme. By 1981, before PCM was introduced, we modelers were permitted to use Frequency Modulation as well as AM. The FM R/C system actually uses FM/FSK where FSK stands for Frequency Shift Keying. FM/FSK is also used for PPM encoding. This simply means that, for each modulation pulse, the frequency of the transmitted signal is shifted about 3KHz; from 1.5 KHz above to 1.5 KHz below the center frequency. The other variant is that some manufacturers shift from low-to-high vs. high-to-low just to be different from the competition. True PCM in the normal communications lexicon means that an analog signal is sampled periodically and its amplitude is converted to a digital word of a certain length; i.e., the greater the amplitude, the higher the digital number. Several channels can be multiplexed and merged with a ”start bit” and “end bit” to describe the start and end of a message segment. There is considerable controversy as to whether PCM as an encoding scheme offers any unique advantage.

Do you sell a PCM receiver?

No. Every manufacturer has a different code for their PCM and in different radio systems manufactured by the same manufacturer. It is not practical to have an after market receiver to accommodate such a wide array of different codes. Fortunately, just one generation of PCM-only transmitters was produced. The first one to come out with a transmitter that could be switched to PPM put an end to that! As far as we know, every PCM transmitter today can be switched or programmed to operate as PPM. Check the manual for your transmitter to find out. If it can be operated PPM, our receivers will afford better performance than the O.E.M. (Original Equipment Manufacturer) receiver whether PPM or PCM.

What is DSR?

DSR stands for Digital Signature Recognition and is the latest technology for secure receiver decoding. Developed and implemented exclusively in FMA Flight System receiver products, DSR works with any standard FM transmitter, is affordable, and provides interference rejection far beyond any other method of decoding used in the R/C industry to date. On startup, Flight System receivers check for valid data. DSR locks on to your unique transmitter characteristics such as FM shift, channel count, pulse widths, and frame length. During flight, DSR compares the received data against stored DSR variables. If an anomoly is encoutered, DSR invokes 4 levels of error correction that can actually repair damaged data and re-construct frame information. This approach is only possible through the advancement of powerful microcomputers used in Flight System receivers. The method is faster and smarter than PCM or any other method for secure data decoding. In addition, all DSR based receivers from FMA support fully programmable failsafe on all channels. Failsafe is simple to setup and uses the controlling transmitter as an interface during the process. Enter failsafe setup mode by holding down the programming button as you apply receiver power. Move the transmitter channel you wish to program. Put the servo where you want it for failsafe condition and press the button again. That's all there is to it. You can read more about DSR technology by visiting the support section of the FMA Direct website and downloading the "FMA Flight System White Paper".

What is the difference between a single conversion and a dual conversion receiver?

ALSO SEE THE SUPPORT SECTION FOR A TUTORIAL REGARDING SINGLE AND DUAL CONVERSION. The single conversion receiver uses a single Local Oscillator at 455 kHz removed from the transmitter frequency to achieve narrow band and high sensitivity. A dual conversion receiver has two local oscillators. The first L.O. is 10.7 MHz removed from the transmitter frequency to overcome the one weakness of single conversion; i.e., the lack of rejection at the image frequency. Image for single conversion is only 910 kHz removed from the transmitted frequency while, for dual conversion, it is 21.4 MHz from transmitted frequency and much easier to filter. The 2nd IF allows the rejection of adjacent channels more readily.

Is there a problem with single conversion receivers?

There is one situation where any single conversion receiver is open to interference that a dual conversion is not and that is at image frequency. JR and FMA have both had highly successful single conversion receivers for many years. Most car receivers have been single conversion over the years because the 75 MHz band is only 500 KHz wide; not enough to have the image frequency inside the band of interest. Since the 72 MHz band is 1 MHz wide, an improperly placed LO can permit image interference within the band. ( i.e., 455 KHz X 2= 910 MHz)

Does FMA make dual conversion receivers?

The Intermediate Frequency (IF) for our Dual Conversion (DC) model receivers has always been 10.7 MHz which means our dual conversion receivers have image rejection of 60 db or better. FMA introduced in Y2K, a new series of Dual Conversion receivers in two models: Magnum and Quantum. The Magnum is available as six or eight channels and automatically handles the FSK shift for all FM transmitters. The Quantum is also available as 6 or 8 channels and specific to a given transmitter so that we can make it as small and light as possible. Weight is 15 grams or less for any model, but all are full performance and can be flown in a quarter scale aircraft if you want. The NEW Extreme four and Extreme 5 receivers are the smallest, lightest dual conversion receivers available.

When will a single conversion receiver be bothered?

When transmitters are operated in close proximity to each other, they generate intermodulation with each other that is re-amplified by the transmitter output transistor. This intermod can fill the spectrum well beyond the image frequency and can interfere with a single conversion receiver. The solution is to keep transmitters separated by 20 ft or so or use a dual conversion receiver in your application.

Will a Futaba, JR, or Airtronics crystal work in my FMA receiver?

No. The only crystals that work in FMA receivers are FMA crystals with the following exceptions:

Dual conversion crystals from Hitec and DAD will work in FMA dual conversion receivers; i.e., Interceptor, micro 2000, Fortress series, Quantum series, and Magnum series.

Tetra single conversion, low profile crystals are not interchangeable with any FMA dual conversion receivers.

Will my standard height or new low profile dual conversion crystal work in my Tetra receiver?

No. Only low profile, single conversion Tetra series crystals work in the Tetra receiver.