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Homemade On board telemetry System

Discussion about Tx, Rx, Servo's, Batteries, Chargers, and all the other things we like to talk about..
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jimbo
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Re: Homemade On board telemetry System

Post by jimbo »

I think barry won't be happy until I buy a taranis (which I won't lol ).
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Barry_Cole
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Re: Homemade On board telemetry System

Post by Barry_Cole »

jimbo wrote:I think barry won't be happy until I buy a taranis (which I won't lol ).
In the end you will.......

BC
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jimbo
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Re: Homemade On board telemetry System

Post by jimbo »

I finally got round to testing this out in the swift. Winds light 8mph so ideal. The range is excellent right above my head. I probably up to 300 to 400ft. However once I s started to fly away the signal was quickly . Obviously as you fly away the distance increases for the same height, ie trig.. so I flew low and farther out, signal still lost even though distance was less than 300ft.
Pity, it's usable but as mentioned you'd need to fly overhead to get a reading. Better than landing I suppose. Gonna put one together with a nano, for the asw 20.
:D
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Peter Balcombe
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Re: Homemade On board telemetry System

Post by Peter Balcombe »

Jimbo,
Remember that the radiation pattern of your aerials will be doughnut shaped, with maximum radiation/receive sensitivity at right angles to the length axis of the wire, with minimum out the ends of the wire core centreline.
Thus, if both your aerials are in the horizontal plane, you will get maximum range with the receiver above you (aircraft aerial axis at right angles to your ground aerial axis, but as the aircraft goes directly away from you, your position relative to it will reduce from 90 degrees with respect to its antenna wire length axis, to near end on, thus into the minimum strength area.
If you fly the model across the slope, or in a circle around you, you should be able to replicate the overhead range.

In practice, I would have thought you are doing pretty well to get 300ft with the simple low power modules.
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jimbo
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Re: Homemade On board telemetry System

Post by jimbo »

Yes, come to think of it i did have the RX wire laid flat on the ground. So some sort of freestanding item is probably needed, would somthing like this improve reception.
http://www.ebay.co.uk/itm/Antenna-433Mh ... SwSgJXNwRg
I was surprised the range in the outward plane, ie forwards with the aerial flat was extremely poor compared to the striaght up range. I mean like less than 50ft.
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Barry_Cole
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Re: Homemade On board telemetry System

Post by Barry_Cole »

Taranis!!!!!!

BC
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jimbo
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Re: Homemade On board telemetry System

Post by jimbo »

@Barry - Behave!!

These nanos are seriously power in tiny packet, with a 2s mini lipo, whole lot will fit in a matchbox.
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Peter Balcombe
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Re: Homemade On board telemetry System

Post by Peter Balcombe »

Jimbo,
I was forgetting that you had the Tx in the plane & Rx on the ground, but the antenna radiation pattern info is still relevant.
I am no antenna man, but I don't think you really want the Rx antenna right on the ground, but at least a couple of feet or more above it.
As I said before, you need the two aerials to be parallel to each other (either both horizontal, vertical, or the same angle in between) for best range.

The main difficulty you will have with fitting any commercial antenna, is the lack of a good 50 ohm impedance connection to your board(s). You really need a matching SMA connector & in order to achieve good impedance matching (& therefore avoid sensitivity loss) you also need a 50 ohm RF connection to this. If you just cut off the cable connector then you are likely to get an impedance mismatch of some kind, hence losing efficiency. Note that the 50 ohms is an AC impedance at 433MHz, not a DC resistance!!
A point to note with commercial antennae is that not all will give you what you might expect.
This tends to be the case with 'rubber duck' types which are shorter than a 1/4 wavelength. The shorter length is often achieved by winding part of the aerial as a coil (similar to that in link picture) although hidden inside a plastic casing which, whilst using a 1/4 wavelength long wire, usually trades off antenna efficiency for compactness and robustness.
The linked antenna states a +3dB gain, but relative to what?
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Peter Balcombe
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Re: Homemade On board telemetry System

Post by Peter Balcombe »

[quote="Peter Balcombe"]Jimbo,
Remember that the radiation pattern of your aerials will be doughnut shaped, with maximum radiation/receive sensitivity at right angles to the length axis of the wire, with minimum out the ends of the wire core centreline. ..........
If you fly the model across the slope, or in a circle around you, you should be able to replicate the overhead range.[/quote]

Correction:
Forget the flying in a circle bit as you should only get good range in two areas (say directly in front or directly behind) when the two antennae are parallel to each other! Worst range likely to be at 90 degrees to those points, when looking at ends of antennae.
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Peter Balcombe
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Re: Homemade On board telemetry System

Post by Peter Balcombe »

Jimbo,
An update on 433MHz module range tests.
I have achieved approx. 300m with RFM69CW transceivers (20mW output) and 900m with the 'CW' replaced by a RFM69HW (100mW output) at the sending end.
Measurements were conducted with a simple 1/2 wave dipole at each end, operating at 433.0MHz, sending 10 byte data packets at 9600 baud data rate. Both antennae in horizontal polarisation and in clear line of sight with each other.
Range will obviously be less in each case with a shorter monopole antenna.
The RFM69 modules are only about 30mm square, so the antenna is the largest component at 165mm long for a monopole & 330mm for a centre fed (non folded) dipole.
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