I did some more random measurements on my BPF today as I was not happy with the earlier results. Although previously I had tuned all the coils such that a definite band pass was obtained for each of the bands, the insertion loss in most cases seemed to be higher than I had expected, As the tuning of the coils had remained untouched I decided to repeat some of the measurements on the higher bands again but with the BPF reversed. To my surprise with the noteable exception of the 12 and 10 Meter Bands the results in brackets shown as (*) for comparative purposes were quite different. Two thoughts came to mind, had I made an error whilst reading the range setting on one of the channels on my oscilloscope whilst taking some of the previous measurements (10 mV/cm rather than 20 mV/cm which would make an immediate difference of 6 dB) or is my tuning technique somehow to blame. So I need to take a deep breath and think about this some more and perhaps repeat all the measurements again before I start altering any core settings.
80 Meter Band
KHz Vin mV pp Vout mV pp Loss dB
3,500 720 230 9.9
3,600 590 300 5.8
3,700 550 320 4.7
3,800 660 230 9.1
40 Meter Band
KHz Vin mV pp Vout mV pp Loss dB
7,000 800 250 10.2
7,100 710 320 6.9
7,200 680 320 6.6
7,300 760 240 9.9
30 Meter Band
KHz Vin mV pp Vout mV pp Loss dB
10,000 800 190 12.4
10,100 630 210 9.6
10,200 570 130 12.8
20 Meter Band
KHz Vin mV pp Vout mV pp Loss dB
13,900 (1100) (270) (12)
14,000 860 (1060) 510 (340) 4.6 (9.9)
14,100 790 (980) 600 (430) 2.4 (7.1)
14,200 800 (940) 620 (510) 2.2 (5.4)
14,300 860 (1000) 550 (460) 3.9 (6.7)
14,400 900 (1060) 450 (350) 6.0 (9.6)
14,500 (1100) (260) (12.4)
17 Meter Band
KHz Vin mV pp Vout mV pp Loss dB
17,900 (1040) (170) (15.9)
18,000 580 (960) 380 (220) 3.6 (12.8)
18,100 640 (960) 360 (210) 5.0 (13.2)
18,200 660 (1000) 300 (160) 6.9 (15.9)
15 Meter Band
KHz Vin mV pp Vout mV pp Loss dB
21,000 480 (880) 190 (130) 8.0 (16.5)
21,100 430 (880) 230 (130) 5.5 (16.5)
21,200 440 (760) 250 (190) 4.9 (12)
21,300 480 (760) 240 (170) 6.0 (13.2)
21,400 500 (820) 200 (140) 8.0 (15.4)
21.500 480 (840) 160 (110) 9.6 (17.7)
12 Meter Band
KHz Vin mV pp Vout mV pp Loss dB
24,800 280 (260) 195 (190) 3.1 (2.7)
24,900 290 (240) 200 (190) 3.2 (2)
25,000 275 (260) 205 (190) 2.5 (2.7)
25,100 350 190 5.4
10 Meter Band
KHz Vin mV pp Vout mV pp Loss dB
28,000 325 150 6.7
28,500 215 190 1.1
28,700 (250) (210) (1.5)
29,000 270 215 1.9
29,500 365 180 6.2
29,700 365 150 7.7
Wednesday, 30 March 2011
Monday, 28 March 2011
Picture of the Test Setup used for my earlier BPF Measurements
I have added the picture above to show the test setup used for obtaining the measurements detailed in my previous blog. The picture was taken whilst testing the response of the BPF at 7.1 MHz. A crocodile clip supplying 5 volts to the 40 Meter BPF PCB Band Select Pin can be seen temporarily connected to activate the appropriate switching diodes for this purpose. Two terminating resistors (I cheated and used 47 ohm rather than ideally 50 ohm !) can be seen temporarily soldered to the input and output ports of the BPF on the underside of the PCB. The oscilloscope probes set at x10 are shown connected to and monitoring the voltage across these resistors on the two channels of the oscilloscope which are both set to display at 10mV / cm. The larger trace on the oscilloscope therefore represents an actual input signal voltage of 710 mV peak to peak and the smaller trace an output signal voltage of 320 mV peak to peak going to and coming from the BPF when connected to the DDS which is shown set to deliver a CW output of 7.100000 MHz. The insertion loss of the filter when measured under these conditions thus appears to be approx 6.9 dB. Also note the 180 degree phase reversal which has occured to the signal during its passage through the BPF.
G6LBQ 9 Band BPF Project
This project is based on a design by Andy G6LBQ and employs a prototype PCB supplied by Sunil VU3SUA and Inductors supplied by Spectrum Communications in the UK and is primarily intended for use in the G6LBQ Multi Band BITX but could be used in conjunction with any ham band receiver or transceiver where a diode switched BPF is required.
I received the prototype PCB kindly donated by Sunil from India during thr first week of March 2012. As I had earlier already purchased the coils in a joint buy with Andy from Spectrum Communications in anticipation of the PCB being produced, I was quickly able to confirm that all coils and components I had on hand fitted perfectly to the PCB.
The special BA243 PIN diodes and NPO ceramic capacitors required to complete the build were then procured from local UK distributors and Ebay auctions using the values that had been computed by Andy and checked earlier by myself. These were delivered and fitted without difficulty to the board the following week. The PCB is laid out to accomodate 0.2 inch (5mm) spaced capacitors throughout and I used Ceramic NPO Disc capacitors for the lower filter values and Ceramic Multilayer NPO capacitors for the higher filter values and Ceramic Multilayer Y5V capacitors for coupling and de-coupling purposes.
Rather than use the 470 ohm and 390 ohm resistor value combination to forward bias the PIN diodes as recommended in Andy's BOM based on operation from 12 volts I chose instead to use 100 ohms and 330 ohms so that I could still operate and switch them at 10 mA from 5 volts provided by the output band switch control PIC utilised in my recently completed VU3CNS DDS.
Apart from fitting the coils used for 160 meters, my BPF PCB assembly is now complete and I have carried out some provisional tests this weekend using my VU3CNS DDS as a signal generator and Tektronix Model 465 Oscilloscope to align and evaluate it's performance as a stand alone unit.
To do this I terminated both input and output ports of the BPF with 50 ohm resistors and across each resistor connected x10 probes which in turn are connected to each of the 2 channel inputs of my scope. I then connected the output of my DDS set to 3.5 MHz to the input port of the BPF and applied a 5 volt DC signal to the 80 meter Band Selector Port and observed the resultant traces on the oscilloscope whilst adjusting each of the corresponding band coil cores for maximum output from the BPF. I repeated the procedure several times using signals up to 3.8 MHz from the DDS until a compromise was reached whereby the reponse of the BPF was as uniform as possible and attenuation least between the edges of the band.
The remaining bands were then aligned similarly.
Whilst performing this alignment I noticed interaction between all three of the band coils, adjustment of the centre coil seemed to have most effect on the output amplitude. However near resonance the input voltage amplitude of the BPF was also found to be notably more diminished and this was also found to be most effected by adjustment of the core nearest to the input, presumably both effects being as a result of loading on the DDS output due to the input impedance of the BPF becoming lower at resonance than that provided solely by the 50 ohms fixed resistor when the BPF is not near resonance.
I have taken this into account when computing the attenuation loss in the BPF for all the Bands aligned in this manner and the results are as follows.
80 Meter Band
KHz Vin mV pp Vout mV pp Loss dB
3,500 720 230 9.9
3,600 590 300 5.8
3,700 550 320 4.7
3,800 660 230 9.1
40 Meter Band
KHz Vin mV pp Vout mV pp Loss dB
7,000 800 250 10.2
7,100 710 320 6.9
7,200 680 320 6.6
7,300 760 240 9.9
30 Meter Band
KHz Vin mV pp Vout mV pp Loss dB
10,000 800 190 12.4
10,100 630 210 9.6
10,200 570 130 12.8
20 Meter Band
KHz Vin mV pp Vout mV pp Loss dB
14,000 860 510 4.6
14,100 790 600 2.4
14,200 800 620 2.2
14,300 860 550 3.9
14,400 900 450 6.0
17 Meter Band
KHz Vin mV pp Vout mV pp Loss dB
18,000 580 380 3.6
18,100 640 360 5.0
18,200 660 300 6.9
15 Meter Band
KHz Vin mV pp Vout mV pp Loss dB
21,000 480 190 8.0
21,100 430 230 5.5
21,200 440 250 4.9
21,300 480 240 6.0
21,400 500 200 8.0
21.500 480 160 9.6
12 Meter Band
KHz Vin mV pp Vout mV pp Loss dB
24,800 280 195 3.1
24,900 290 200 3.2
25,000 275 205 2.5
25,100 350 190 5.4
10 Meter Band
KHz Vin mV pp Vout mV pp Loss dB
28,000 325 150 6.7
28,500 215 190 1.1
29,000 270 215 1.9
29,500 365 180 6.2
29,700 365 150 7.7
The losses for some of the above bands seem to be higher than I would have expected whilst in other cases they seem to be lower, so I am open to any suggestions as to why this might or appear to be so and any comments regarding the validity of my measurement and alignment techniques would be appreciated.
The reason why I have not fitted the 160 Meter coils as yet is because according to theory ideally the windings on the coupling coils should each have an extra 3 turns as they are lacking on the standard coils chosen from those currently available from Spectrum Communications. Since these particular coils do not have screening cans fitted it would be comparitively easy to add the extra turns before the coils are fitted if later should I decide to do so.
In the meantime I would like to try in the next day or so to use the BPF in conjunction with an antenna and my G6LBQ transceiver PCB assembly and VU3CNS DDS to access it's performance in practice.
Finally a big thank you to Andy and Sunil without whose help this project would not have been possible.
I received the prototype PCB kindly donated by Sunil from India during thr first week of March 2012. As I had earlier already purchased the coils in a joint buy with Andy from Spectrum Communications in anticipation of the PCB being produced, I was quickly able to confirm that all coils and components I had on hand fitted perfectly to the PCB.
The special BA243 PIN diodes and NPO ceramic capacitors required to complete the build were then procured from local UK distributors and Ebay auctions using the values that had been computed by Andy and checked earlier by myself. These were delivered and fitted without difficulty to the board the following week. The PCB is laid out to accomodate 0.2 inch (5mm) spaced capacitors throughout and I used Ceramic NPO Disc capacitors for the lower filter values and Ceramic Multilayer NPO capacitors for the higher filter values and Ceramic Multilayer Y5V capacitors for coupling and de-coupling purposes.
Rather than use the 470 ohm and 390 ohm resistor value combination to forward bias the PIN diodes as recommended in Andy's BOM based on operation from 12 volts I chose instead to use 100 ohms and 330 ohms so that I could still operate and switch them at 10 mA from 5 volts provided by the output band switch control PIC utilised in my recently completed VU3CNS DDS.
Apart from fitting the coils used for 160 meters, my BPF PCB assembly is now complete and I have carried out some provisional tests this weekend using my VU3CNS DDS as a signal generator and Tektronix Model 465 Oscilloscope to align and evaluate it's performance as a stand alone unit.
To do this I terminated both input and output ports of the BPF with 50 ohm resistors and across each resistor connected x10 probes which in turn are connected to each of the 2 channel inputs of my scope. I then connected the output of my DDS set to 3.5 MHz to the input port of the BPF and applied a 5 volt DC signal to the 80 meter Band Selector Port and observed the resultant traces on the oscilloscope whilst adjusting each of the corresponding band coil cores for maximum output from the BPF. I repeated the procedure several times using signals up to 3.8 MHz from the DDS until a compromise was reached whereby the reponse of the BPF was as uniform as possible and attenuation least between the edges of the band.
The remaining bands were then aligned similarly.
Whilst performing this alignment I noticed interaction between all three of the band coils, adjustment of the centre coil seemed to have most effect on the output amplitude. However near resonance the input voltage amplitude of the BPF was also found to be notably more diminished and this was also found to be most effected by adjustment of the core nearest to the input, presumably both effects being as a result of loading on the DDS output due to the input impedance of the BPF becoming lower at resonance than that provided solely by the 50 ohms fixed resistor when the BPF is not near resonance.
I have taken this into account when computing the attenuation loss in the BPF for all the Bands aligned in this manner and the results are as follows.
80 Meter Band
KHz Vin mV pp Vout mV pp Loss dB
3,500 720 230 9.9
3,600 590 300 5.8
3,700 550 320 4.7
3,800 660 230 9.1
40 Meter Band
KHz Vin mV pp Vout mV pp Loss dB
7,000 800 250 10.2
7,100 710 320 6.9
7,200 680 320 6.6
7,300 760 240 9.9
30 Meter Band
KHz Vin mV pp Vout mV pp Loss dB
10,000 800 190 12.4
10,100 630 210 9.6
10,200 570 130 12.8
20 Meter Band
KHz Vin mV pp Vout mV pp Loss dB
14,000 860 510 4.6
14,100 790 600 2.4
14,200 800 620 2.2
14,300 860 550 3.9
14,400 900 450 6.0
17 Meter Band
KHz Vin mV pp Vout mV pp Loss dB
18,000 580 380 3.6
18,100 640 360 5.0
18,200 660 300 6.9
15 Meter Band
KHz Vin mV pp Vout mV pp Loss dB
21,000 480 190 8.0
21,100 430 230 5.5
21,200 440 250 4.9
21,300 480 240 6.0
21,400 500 200 8.0
21.500 480 160 9.6
12 Meter Band
KHz Vin mV pp Vout mV pp Loss dB
24,800 280 195 3.1
24,900 290 200 3.2
25,000 275 205 2.5
25,100 350 190 5.4
10 Meter Band
KHz Vin mV pp Vout mV pp Loss dB
28,000 325 150 6.7
28,500 215 190 1.1
29,000 270 215 1.9
29,500 365 180 6.2
29,700 365 150 7.7
The losses for some of the above bands seem to be higher than I would have expected whilst in other cases they seem to be lower, so I am open to any suggestions as to why this might or appear to be so and any comments regarding the validity of my measurement and alignment techniques would be appreciated.
The reason why I have not fitted the 160 Meter coils as yet is because according to theory ideally the windings on the coupling coils should each have an extra 3 turns as they are lacking on the standard coils chosen from those currently available from Spectrum Communications. Since these particular coils do not have screening cans fitted it would be comparitively easy to add the extra turns before the coils are fitted if later should I decide to do so.
In the meantime I would like to try in the next day or so to use the BPF in conjunction with an antenna and my G6LBQ transceiver PCB assembly and VU3CNS DDS to access it's performance in practice.
Finally a big thank you to Andy and Sunil without whose help this project would not have been possible.
Saturday, 19 March 2011
DDS project
I have created this blog to record and illustrate various stages in the construction of my latest DDS project which is based on an Analogue Devices AD9851 controlled by PIC16F628A microcontrollers with firmware created by VU3CNS and PCBs supplied by Sunil VU3SUA.
The following picture shows test signals from the part assembled PCBs being observed and measured on my kitchen table in late January 2011.
The following picture shows test signals from the part assembled PCBs being observed and measured on my kitchen table in late January 2011.
The PICs were programmed using my Picket3 clone and the keypad used in the tests was taken from a scrapped telephone and the LCD module was bought new on Ebay from a supplier in Hong Kong.
Once it was established that this lashup functioned ok it was time to think about a suitable enclosure and how best to package up all the parts.
It was my intention to eventually use this DDS as a VFO for a multiband BITX project based on either the 2E0ZHN smd or a G6LBQ version both of which I have already built and tested earlier using a N3ZI DDS but which lacked an output to automatically switch BPFs or LPFs.
As I previously had some experience in using the Aluminium cases supplied by Maplin I decided that their box type AB13 order code LF14Q measuring 6 x 4 x 2 inches would be suitable, so on that basis before I did any serious metal bashing I made up a mockup of what I had in mind to get an idea of part placements using PCB spacers and Blutack to assist in locating and affixing all of them.
The photos above show the mockups. Note in order to squeeze the PCBs into the standard Maplin case, about 1/8 inch of the flanges needed to be removed from the top of the end sides of the lower half of the case, but otherwise it is a perfect candidate for the job.
The mockup D Sub Connector housing shown attached to the rear of the box is how and through which all the output and input control lines for the BPFs and LPFs will be routed. I realised early on that although this DDS provides positive 5 volt signals for this purpose they are limited by the PICs to 25 mA maximum and therefore in order to drive relays for LPFs etc some level changing would need to be employed eventually. This I reckoned could be best done externally and most neatly utilising a ULN2803 Darlington Driver Array as an add on module built into a D sub connector housing to suit individual interface circumstances as they arose.
The next job was to mark out and hand drill and file all the holes and apertures required for mounting the parts. All this work was done using hand tools on the kitchen table during late February and early March 2011.
The aluminium box was washed and cleaned ready for a trial fit of all chassis and panel parts and sub assemblies. Miniature LEDS used to display the Band selected were mounted on a piece of perf board and connected to the D Sub 25 way connector which in turn connects to the main DDS PCBs using Molex connectors.
The main PCBs were then stacked using metal and nylon spacers ready for connecting to the subassemblies and final installation inside the case.
The photos below show the DDS finally assembled, powered up and working.
DDS tuned to 28.000000 MHz
Scope display of output of DDS tuned to 28.000000 MHz
Scope display of output of DDS tuned to 7.000000 MHz
DDS tuned to 7.000000 MHz showing the LED for the 40 Meter Band illuminated
DDS tuned to 14.000000 MHz showing the LED for the 20 Meter Band illuminated
My next job is to use this DDS as a signal generator to align and test a prototype G6LBQ Multiband BITX BPF PCB which I recently received this month from Sunil and which I have since populated and assembled and am now ready to test.
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