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Interferometer using AD8302 board update
¿ªÔÆÌåÓýI think I'm a step towards sorting this out - new AD8302 phase comparator board. Taken much of stuck off old layout and starting as simply as possible. Found I had stabilised 5V power supply in shack - very convenient.
Labjack U3 and Radio Sky Pipe II software used for these tests and my Dell Inspiron laptop.
Started with nothing attached to either RF input not even dummy load, as per advice from Jan Lustrup (thanks Jan for your advice!) Also didn't bother with any case for these first tests.
So, firstly confirmed that both signal outputs (phase and total power) are 0.96 V or thereabouts compared to ground, consistent with the bias voltage known to be on these lines.
I then added a RF signal generator to the RF lines - used a power Splitter so same signal to both RF inputs to AD8302. Total power went up, phase stayed same.
Added Attenuator between power Splitter and AD8302 - changing attenuation changes power detected on PC.
Changing frequency from 1420MHz to 420MHz on RF signal generator made no difference.?
Now took out power Splitter and added 2nd RF signal generator to 2nd RF input on AD8302. Turning one or other of the signal generators changes total power and power on phase lines in ways I don't understand. Changing RF frequency
on one of RF signal generators eg by 2MHz seems to make little or no difference. No interference fringes seen.
I don't understand the last set of findings. If anyone can help me it?would be greatly appreciated.
Andy
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Hi Andrew.
Those results look good.
To understand the final test (different frequencies in the two arms of the phase detector) it is better to think of a phase detector as an RF mixer. The device will output the sum and difference frequencies, these?will be 2MHz and 2842MHz (plus many other harmonically related frequencies). ? However because of the intended use of a phase detector these high frequencies are filtered out so you don't see any output in your test.
To work it will expect to see the same frequency (1420MHz) on both arms. If you put in two signals differing by 1Hz you would see a 1Hz sine wave on the output, but this is very difficult to achieve with the stability of typical amateur signal sources.
In use, the output from the two antennas is at the same frequency and as the relative phase of the signals changes you see a change in the DC output. So to test this connect the same source to both inputs and record the dc output. Then change the length of the cable to one arm This will change the relative phase of the two signals and you should see a change in the output.?
Let us know how you get on. Melvyn
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¿ªÔÆÌåÓýThanks Melvyn ? From: [email protected] <[email protected]>
On Behalf Of melvyn.jones via groups.io
Sent: 08 January 2024 17:04 To: [email protected] Subject: Re: [baa-rag] Interferometer using AD8302 board update ? Hi Andrew. Those results look good. To understand the final test (different frequencies in the two arms of the phase detector) it is better to think of a phase detector as an RF mixer. The device will output the sum and difference frequencies, these?will be 2MHz and 2842MHz (plus many other harmonically related frequencies). ? However because of the intended use of a phase detector these high frequencies are filtered out so you don't see any output in your test. To work it will expect to see the same frequency (1420MHz) on both arms. If you put in two signals differing by 1Hz you would see a 1Hz sine wave on the output, but this is very difficult to achieve with the stability of typical amateur signal sources. In use, the output from the two antennas is at the same frequency and as the relative phase of the signals changes you see a change in the DC output. So to test
this connect the same source to both inputs and record the dc output. Then change the length of the cable to one arm This will change the relative phase of the two signals and you should see a change in the output.? Melvyn |