radio-ham autotuner for magloops

Benjie

Senior Member
For those interested, I built an automatic tuner for magnetic loop antennas.
Using a 28X1 it drives a DC motor moving the high voltage tuning capacitor on the antenna until it gets to the SWR minimum. By storing the previously tuned frequency and the new frequency it drives the motor in the right direction so that it can be used with large value tuning capacitors covering more than one band.
To anyone interested, I can e-mail all data, code and pcb layout.

IZ3BGJ
 

KMoffett

Senior Member
To anyone interested, I can e-mail all data, code and pcb layout.

IZ3BGJ
Benjie,

The concept of a forums is to share your designs with the people here now, and those who are looking for ideas in the future. Please "post" your design concepts, schematics, and code here. :)

Ken
 

Benjie

Senior Member
You are right,
attached is the schematic and here the code; hope you can copy it.

Code:
init:
symbol mot1=6 		'motor wire 1
symbol mot2=7		'motor wire 2
symbol imp=0		'pwm drive 	
symbol green=2		'green "tuned" led
symbol red=5		'red led
symbol yel=3		'yellow led
symbol newfreq=w1			
symbol oldfreq=w0
symbol auto=pin0	'auto switch
symbol rf=pin5		'RF carrier detector
symbol tunecmd=pin2	'"tune" push button	
symbol manl=pin1	'manual low speed switch
symbol newswr=b8
symbol oldswr=b7
symbol imph=b5
symbol impl=w7
setfreq em16

'at power-on ensure that the antenna is tuned via 
'MANUAL operation:blink all leds if auto switch was left to AUTO 

do 
high red:high yel:high green:pause 300
low red:low yel:low green:pause 300
loop while auto=1 

main:

'set pwm as function of operating band
do
	high red:pause 300
	low red:pause 300
loop while rf=0	
	
manual:
high imp:high yel
if manl=1 then
	do
		high imp:high yel:pause 50
		low imp:low yel:pause 300 
	loop while manl=1
endif
if auto=0 then goto manual
do loop while rf=0 or tunecmd=0
	count 4,400,oldfreq:high green
wait 2
adjust:
if auto=0 then goto manual
do loop while rf=0 or tunecmd=0
high red
		count 4,400,newfreq
		'if newfreq=oldfreq then goto adjust
		if newfreq>oldfreq then high mot1:low mot2:endif
		if newfreq<oldfreq then high mot2:low mot1:endif

	do
		readadc 3,oldswr
		if oldfreq<2000 then 
			let imph=oldswr*2+10 max 254 	
			let	impl=255-oldswr
		endif
		if oldfreq>2000 then
			imph=oldswr max 254
			impl=700-oldswr
		endif
		low yel
		high imp:pause imph:high yel
		low imp:pause impl:low yel
		readadc 3,newswr
			'pause 300
	loop while newswr<oldswr or newswr>30
low mot1:low mot2
oldfreq=newfreq
low red:high green
if auto=0 then goto manual
goto adjust
 

Attachments

MPep

Senior Member
Cool project. You forgot to close with a [/code].
What did you use for the sensing system? Coil around the feed-wire? Ffrequency range?
 

Benjie

Senior Member
This is the second unit that I make. In the first one I used a small iron oxide core on the transmission line with few turns, in the second that I posted here I use a 6" RG174 coax connected as per the diagram. This last one is easier to calibrate; it is essential that the sensing unit is well screened from the rest of the circuit because of its high RF content.
I forgot a detail: so far it operates correctly on the 80m and 40m amateur bands. The antenna loop in use is a 1.5m diameter Aluminum pipe of 1" diameter with a 750pF vacuum capacitor.
Sorry for the [/code].
For additional details you can get my data in www.qrz.com call sign IZ3BGJ.
 

malti

New Member
Re Picaxe ATU

Benjie,

I am very much interested in your Picaxe controlled ATU. However I cannot find details how to calibrate/adjust the 1 k variable at the coax bread, and the 47k on the MC33072P. Help please

Paul
 

john2051

New Member
Hi, what an intriguing project. As I have yet to install an hf antenna, ive always been fon of the magloop.
Just one thing concerns me about your cct diagram.
What happens if you press the manual up or down button, which grounds the motor
and the output of the uln2003. I take it theres no chance of a significant short.
I'm really looking forward to this, as ive seen how much less noise there is on a loop
compared to a dipole.

Mank thanks john M0ERS
 

Benjie

Senior Member
Hi malti,
sorry for the late reply, I had many inquiries.
the 1K variable trimmer has to be adjusted for zero SWR signal at the diode cathode when the SWR is 1:1. The 47K on the MC33072 has to be adjusted for 4.5V when SWR is very high...says 20:1.
The SWR detector is the most critical part of the system. I may suggest to make it external and feed its low voltage via a short screened cable to the input of the MC33072 network.

Anselmo
 

Benjie

Senior Member
Hi John, sorry for the late reply.
The outputs of the ULN2803 are open collector darlington transistors and there is no harm in shortening them to ground whichever is their status.
 

Qtext

New Member
automatic tuner for magnetic loop antennas

For those interested, I built an automatic tuner for magnetic loop antennas.
Using a 28X1 it drives a DC motor moving the high voltage tuning capacitor on the antenna until it gets to the SWR minimum. By storing the previously tuned frequency and the new frequency it drives the motor in the right direction so that it can be used with large value tuning capacitors covering more than one band.
To anyone interested, I can e-mail all data, code and pcb layout.

IZ3BGJ
Hi there,
I'm interested!
Thanks in advancd.
Gadi Alon - 4Z7ADA
gadi.alon@gmail.com
 
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