Picaxe for Hams

Can the Picaxe analogue input accept a rectified rf input voltage to control a motorized variable capacitor to bring down an SWR on an antenna tuner ??

malti said:

Can the Picaxe analogue input accept a rectified rf input voltage to control a motorized variable capacitor to bring down an SWR on an antenna tuner ??

Click to expand...

Malti.

A ham will provide a much better answer, but, I'm assuming
that you might be “tapping” the analogue voltage from a
SWR meter?
If so, what voltage range?

e

You cant just put a rectified signal from the antenna into a PICAXE and expect it to read the SWR, for a PICAXE to read the SWR you will have to have some external arrangement of capacitors and inductors to produce a voltage the PICAXE and read and get so get the SWR.

Look here for a PIC based SWR meter, you can just use the analogue front end.

http://products.foxdelta.com/swr-vhf.htm

Thanks Mbrej.
Your post reminded me that I'd seen a Picaxe version,

http://www.users.on.net/~endsodds/analsr.htm

http://www.scarc.org.au/

e

The swr voltage is tapped throu a bridge circuit consisting of a diode and r bridge diagram here : http://web.telia.com/~u85920178/use/swrpwr.gif

malti said:

The swr voltage is tapped throu a bridge circuit consisting of a diode and r bridge diagram here : http://web.telia.com/~u85920178/use/swrpwr.gif

Click to expand...

OK, fine.

What's the maximum voltage across the SWR meter?

e

malti said:

Can the Picaxe analogue input accept a rectified rf input voltage to control a motorized variable capacitor to bring down an SWR on an antenna tuner ??

Click to expand...

Yes, as long as the voltage is in the range of 0 to +5vdc. If it's higher then a resistor divider would be needed to scale the range to fit in 0-5 volts.

Lefty WA6TKD

Thanks all fer info

I tried to put a variable dc in to an 18x, but it could not trigger the outpin at 0 volts. The 18x is supposed to be high resolution analogue in

9H1FQ

Posting your code and exact schematic would help.
Have you checked at ADC-in with a multimeter?

Yes I did measure with a dmm o fcourse. The 18x was triggering the output pins at 0.5 volts and not at 0 volts as programmed

@malti

Please post your code.
Please post the circuit.

e

malti said:

Yes I did measure with a dmm o fcourse. The 18x was triggering the output pins at 0.5 volts and not at 0 volts as programmed

Click to expand...

Can you please explain in DETAIL what you mean by that.
What is triggered? How? What output pins?
What is your power supply. This will affect the ADC reading.
On a 5v supply, the ADC will read around 102 assuming you're using it in 10-bit mode. About 26 in 8-bit mode.

What's your source impedance? Using enhanced download circuit?

As requested by Dippy & eclectic, please provide circuit and code.
Otherwise, we can only guess.

sorry guys I did not finish my swr meter project yet. I am thinking of using an AD8307 logarithmic amplifier as a feed between the swr bridge and the adc picaxe input

Malti,

I can recommend the Tandem Match as a means of separating forward and reverse power. Your suggestion of the AD8307 log amp is a very good one and SWR/power meters using one or more of these ICs have been described – either the ARRL handbook or the excellent "Experimental Methods in RF Design" (or possibly both) and you could also check out the web site of N8LP. I have used the AD8307 as a detector to plot the output of IF filters using a PICAXE-controlled DDS synthesiser to sweep the frequency band.

For any Forum members who are not familiar with log amps such as the AD8307, this is an IC that takes an RF input and which gives a DC output voltage that is related to the log of the RF amplitude. The AD8307 is scaled to give 25mV/dB. Dynamic range is of the order of 70dB. Common applications are in spectrum analyser and radar receiver IF strips. For more information take a look at the Analog Devices web site.

Richard