JLB

My Feedback: (2)

Danny,

I have flown JR equipment for many years and have the utmost confidence
in it. For that reason I have never really considered running dual receivers
in my 35% and 40% aircraft but like a lot of modelers the urge to experiment
is always there. I have heard stories about 2 receivers "talking" to each other
and reduced range etc etc etc. I would like to hear your comments/suggestions
on this subject please. Also curious if one were to try this, would it make any
difference if they used dual conversion or standard receivers. Thanks for
for your input.

dsnyder

It is possible that when using two receivers, that the range of the aircraft may be lowered due to antenna interference. Generally there is at least a slight loss in range, in other installations the reduced range can be significant. For these reasons, we do not recommend dual receiver set ups. Using single vs. dual should not make much difference in a dual receiver set up.

Dennis Mitchell

Danny:

I am building the Nick Ziroli B-25(101) and using the 10X system. It has been recommended that some form of back-up system be utilized, in case the receiver fails. This bird has twin G-26 engines, spit-flaps, ailerons, elevator, twin rudders, dual kill switches, retracts, and airborne cameras. If a second receiver is not recommended, what do you suggest? I am considering Electro-Dynaics opto-isolation on eight channels.

This is because the fuselage is 79" long and will require some very long servo extensions.

dsnyder

The likelyhood of running dual receivers helping save a plane is very slim. The two most suceptable components of a receiver for failure are the crystal and the crystal filter, these fail through vibration or shock. If you keep the receiver well installed with good vibration protection the risk of failure is extremely slim. Adding another receiver however doubles your chances of having a failure. And since range can be reduced with two receivers, your chances of getting holds is increased.

There are a few options, I've heard of people having great success with the opto-isolators that you mention. Other things you can use to improve the set up is to use filters on the leads from the batteries to the receiver, the throttle servo to the receiver, and any leads over 36" long. (JRPA028 and JRPA029) Also running dual batteries and dual switches will increase your redundancy.

Dennis Mitchell

Thanks Danny:

I have been working on this one for a while. I am taking classes in composites technology and building the firewalls out of NOMEX/carbon fiber sandwich with aluminum expanded metal for the spacer between the engine mount and firewall. I am looking at the Zenoah G-26 or equivalent glow engine. Two stroke glow is 1.20 and I believe a four-stroke alternative is 1.80 - 2.00. The "scale" prop should be 19.875"; however, 18-6 should be pretty close.

Have a good week.

dsnyder

Sounds like an awesome project! Good luck with it!

Dangerous Dan

My Feedback: (1)

I know this is an old thread but can somebody explain the theory behind two receivers causing reduced range.

Is the range reduced more with crystaled or synthasized receivers?

Does the receivers locally transmit theit IF(intermidiate or mixing frequency?)


How does synth receivers work without crystals?

If the recievers only receive and do not transmit anything, I can not see how two receivers can cause reduced range. People have said that the two anteannas interfer with each other, but if a receiver does not transmit anything.

So that is the difference between an extra antenna and a metal pull-pull cable as far as reduced range is concerned?

Mac_Man_UK

Inside a receiver there is a local oscillator whose frequency is determined by the plug in xtal. Although it is a low power oscillator, it will radiate some RF and this will be picked up by the other receiver and will raise the noise floor at the front end, and de-sensitize the receiver.

Synth receivers do still have a crystal (or 2 id a Dual Conversion) but this is the CPU crystal. When a scan is inititated, the PLL oscillator will start stepping down in channel frequency. When a signal is detected on that channel it causes the CPU to stop the step down. If the synth receiver happens to be a PCM receiver, the CPU looks at the inbound signal and compares it against its internal coding. If it is not a SPCM signal then it starts to flash the blue light slowly to advise you of this. Vice versa for the PPM receiver...

If the signal is valid then the CPU will memorise the step value so each time you switch on the receiver, it will load the step value into the PLL so that you are at the same frquency as lasttime.

(Edited due to missing word !)