Doppler Shift

  
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Doppler Shift

Postby RichardGold » Tue Sep 30, 2014 11:38 am

Hi everyone,

For a project I have to simulate the effect of a Doppler shift of 1kHz on a receiver. I have the ERA400TRS Modules and dev kit. I was planning on setting a difference of 1kHz between the channel's such as 434.175 kHz on the transmitter and 434.075kHz on the receiver then configuring the bandwidth as a high enough setting to still receive the signal. However I've attempted this and had no luck using easyRadio Companion's communication test. I'm new to using radio modules so any advice would be much appreciated.

Thanks in advance,
Rich
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Re: Doppler Shift

Postby WirelessMike » Thu Oct 02, 2014 11:53 am

The setting of eRA device operating frequency is best done in the Companion Software 'Advanced ERA Frequency Settings' tab.

This generally follows a channelized 'bandplan' that works with the base frequency, the prescribed channels and the bandwidth selected.

We would suggest that you plug in the first module , set the base frequency to 434.1750 MHz an then program the module

Then plug in the second module and set the base frequency to 434.1740 MHz (-1kHz) and then program this second module.

(The absolute transmit and receive frequencies should be within 100Hz of the set frequency)

Then attempt the communications test

I am not sure anyway how useful this will be as the successful reception and decoding of the signal will also depend on the absolute received signal strength.

I assume this is for some sort of satellite telemetry system ?
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Re: Doppler Shift

Postby RichardGold » Thu Oct 02, 2014 1:34 pm

Okay I'll have a go at that, I missed the Advanced ERA Frequency tab.

Yes this is for the design of a free-falling unit that's being ejected for a sounding rocket.

Are there any more details for the receivers on the maximum frequency mismatches?

Many thanks
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Re: Doppler Shift

Postby WirelessMike » Thu Oct 02, 2014 3:26 pm

It might be worth you having a read of the TI CC1101 datasheet ? This gives more information on receive bandwidth sensitivity.

For best range performance you would normally tend to more narrow bandwidth and lower data rates.

In your case it may be worth experimenting with wider bandwidths which will tolerate larger frequency offsets
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Re: Doppler Shift

Postby RichardGold » Tue Oct 07, 2014 10:55 am

Thanks for the help so far,

Like you suggested I've been trying to use the Advanced ERA Frequency settings to simulate the Doppler shift by offsets in the base frequency. However even when I set the base frequencies the same with the same bandwidth, program the module and then try the communications test, no connection is established. I've tried resetting modules after being programmed and am setting both modules to the user defined bandplan "b4" but still had no luck in connecting.

Am I doing something wrong when using these custom bandplans?
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Re: Doppler Shift

Postby RichardGold » Tue Oct 07, 2014 12:57 pm

Just updated the firmware and now works fine, problem solved.
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Re: Doppler Shift

Postby radiomadeeasy » Wed Oct 08, 2014 1:06 pm

Hi RichardGold,

Glad your problem is now fixed. Please let us know if you experience any further issues.

Many thanks.
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