FASST receiver distance apart
 

Hey All,

Wondering if I could get some advice.
I am installing 3ch FASST receivers for the first time and was planning on installing them close together like shown below.
Has anyone experienced issues having them next to each other like this?
I will orientate coax ends at 90 degrees to each other.

Paul.
http://www.rcuniverse.com/forum/atta...mentid=2189100

Paul

I have had a number of planes with twin FAAST receivers installed. Never had any issues with them. Never had a problem with the receivers being positioned like you have. Using twin receivers gives you the opportunity to have the uncovered ends of the coax wire orientated in different directions. The ends should as you say, be at 90 deg from each other. You can now get 3 axis reception with one pointing up, one pointing to the front and one to the side.

John

Paul,

I would suggest, the very reason for multiple receivers, is to improve the potential quality of the signal received. Therefor placing them next to each other like that (even orientating the antenna as you say) will give you limited exposure. At least position them opposing each other and have the antenna exposed to both sides of the model.

Just my 2c.

Jan

Agree with Jan,
having twin (redundancy) receivers and then placing them "at the same spot" removes much of the benefit. Place one aft in the plane and one in the front in two completely different locations, that way if one is in "shadow" the other is probably not. The SBUS wires can be up to 3 meters long for this.

Thanks All,

Great advice!!

Carsten I didnt realise you could have such a long lead from receiver to powerbox..good to know.
John I will do what you recommend and have 1 of the pairs in a vertical orientation.
Jan you make a good point... I like the look of them next to each other and will have to come to terms with their separation :)

Regards,

Paul.

Hi Carsten,

I thought I read somewhere in the futaba literature that the leads should be no longer than 30-40 cm.....or maybe I was told that by our local futaba agent?

SBus is intended to be able to drive servos in the tail with a single cable while the receiver is in the front of the fuselage so it needs to be able to drive cables at least as long as the typical fuselage. It wouldn't be of much use if it could only be used to connect servos within 40cm of the receiver. Connecting between receiver and powerbox is the same as between receiver and servos..

Futaba sells longer antennas that would allow you to keep your receivers where they are and just run the longer antenna leads. Futaba part number -HSP79766 ANT 400MM. You can also purchase a cable that can be used for 2.4 antenna from Digikey http://www.digikey.com/product-detai...554-ND/1657749 they would need to be cut to the length you need and the shielding cut back on the tip. These antennas are coax cables on most Futaba receivers and just plug into the receiver.

Hi Wayne,

I was was speaking of the leads from receiver to powerbox, not sbus lines to servos. They quite obviously can be very long.

If it's a Futaba receiver I was assuming a serial (SBus) connection between the receiver and powerbox. If that isn't the case then sorry for the confusion. If the receiver does connect using SBus that is a serial, digital protocol and the Powerbox uses the same signals/data as an SBus servo and should be able to use similar cable lengths.

Those longer antenna cables and antenna extension cables (even the Futaba ones) come with an associated and not insignificant signal loss. Its much better to move the receiver to a location where the antennas are more clear than to extend the antenna cables...

Bob

Craig,
assuming you are using a "decent" cable between the powerbox and the receiver, you can (according to PowerBox/Emmerich) use up to 3 meters of cable. (And as other writes, the SBUS signal can travel even further, this is the same signal that can be routed around in your plane driving Futaba SBUS servos directly.) Just keep in mind that the cable from the powerbox to the SBUS(2) output on the receiver is up to the job (the receivers can pull up to 200 mA). I use 0.5mm2 cable between "powerboxes" and receivers. The 0.5mm2 is to keep the voltage drop over the 3 meter cable to a minimum.

Hi Carsten,

It must be different for powerbox products; thanks for clarification. I found this reference in the robbe pss2018 instructions which is what had stuck in my mind:

"S-BUS receivers are connected to the PSS2018 by patch cables (Part Nr. 4090,4093 or 4096 – depending on length). See print RX1 and RX2 on housing. Patchcables can be up to 50 cm / 20". This allows for long distances in-between themand therefore for optimal positioning of the antennas. "

Futaba does not warn against using longer antennas. I have seen competition sailplanes (they fly long distances riding thermals) using the 400mm length with no problem. Can you send me a link to information regarding the signal loss data?

Having the longer antenna is definitely better than having the antenna inside a carbon fiber fuselage, but all coax cable has losses, so the longer the cable, the higher the losses. I've seen suggestions that the loss from the coax used on Futaba antennas is around 1.4 dB/foot

Bob

Signal loss for the cable (not sure if it is this exact type, diameter is a close match though (1.13mm). The loss of that is 3.73 dB/meter of cable (at 3 Ghz), so the difference from the "standard" antenna of approx 10 cm length (excluding the "antenna" itself) to a 400 mm long one (40 cm) is:

Extra length is 30 cm. So the extra loss due to the longer antenna is around 1.2 dB. This is insignificant in most of our cases. The change in signal strength will be many dB just moving the plane a little (easily in the order of 10 to 15 dB) and certainly MUCH less than the penalty of bringing the antenna inside the fuse

UFL/cable data: http://www.mouser.com/ds/2/185/U.FL_catalog-939761.pdf