The Si570 is a combined silicon oscillator, that has come to fame in amateur radio circles through its adoption in the SoftRock series of SDRs (or should it really be SDxs)
Silicon oscillators have the property that they are stable, but cannot be manufactures to a precise frequency in the way that quartz can. The Si570 however has an integral frequency synthesizer and so in a tiny package provides oscillator with a computer controlled output frequency.
G4EOP has several interesting pages on the Si570 including some PIC code.
http://g4oep.110mb.com/channels/channels.htm
Saturday, January 29, 2011
Some Si570 Circuits
Monday, January 17, 2011
Crawley Microwave Table - Sunday, September 12, 2010
The Crawley Amateur Radio Club hosted another very successful and enjoyable Microwave Table on September 12th, when yet again we were favoured with good weather and a good attendance which encouraged participants as in previous years to spill out during the informal sessions into the open air on to the forest area immediately surrounding the Clubhouse for ‘eyeball’ chats or outside demonstrations etc.This event is one of several organised each year at different venues in conjunction with the UK uWave Group and we again had visitors from a wide area of the South and South-east, Oxfordshire and East Anglia with a total attendance of around 45 including CARC members which meant that we had pretty well a full house for the formal technical presentations in the afternoon session.
The general format was similar to that of previous years with an informal session in the morning with tables laid out for the ‘bring and buy’ sale in parallel with an exhibition of home constructed equipment being entered into the competition for the annual G3VVB trophy.
For those not familiar with the history of the trophy, it is awarded annually in memory of Cyril, G3VVB by the judges who in their opinion, entered the best made piece of home construction in the contest. The actual trophy is a beautifully engineered microwave power amplifier cavity in manufactured in highly polished brass intended to accept a ceramic 2C39 valve representative of the many that Cyril used to make each year for the amateur fraternity which enabled many would-be “microwavers” to get on air on 23cm or in the case of your scribe, on 13cm with the moderately high power level for those days of 35W SSB before the days of an affordable solid state PA! 
After the lunch break, the results of the constructional contest are usually announced followed by the presentation of the trophy to the winner and then the main technical session with several technical talks until the close at around 16-30pm.This year the doors opened at 10-00am as usual and by the nominal start time of 10-30am, the tables were almost full of a wide variety of items being offered for sale and the Coffee bar was in full swing with cups tea and bacon butties etc. disappearing at a rate of knots to satisfy the pangs of hunger of the early starters. As usual our two stalwarts Ted Macdonald G4TTY and Dick Lupton M0RXZ manning the coffee were kept pretty busy
Meantime, the informal chat session was well under way with old friends meeting up again and bargains on offer being picked over, - this being a good place to pick up microwave bits not readily available through main dealers.
Around a dozen exhibits were entered into the constructional display with again some excellent examples of home brew in the microwave field on display for the Judges including the trophy itself. Covering a wide range of complexity, the items being judged ranged from a nicely made Mini VNA network analyser through to a magnificent 500W 23cm MOSFET linear amplifier for masthead mounting with a remote a control unit and calibrated power meter.
During the lunch break Ted and Dick were again kept busy in serving their famous burgers and bacon rolls etc. after which the result of the G3VVB constructional contest was announced by the chairman of the judges Allan Wyatt, G8LSD and the trophy presented to the overall winner of the competition, John G3XDY for his 23cm amplifier.
There were three technical papers presented in the afternoon session. The first of these was entitled “What To Do With a Big Dish” by Mike Willis who works at the Rutherford-Appleton Research Laboratory and who described how he made the most of an unusual opportunity recently in having access to one of RAL’s large steerable microwave dishes to use on the amateur microwave bands for a weekend and some the results of the troposcatter and EME signal paths he explored .
The second paper was given by Sam Jewell, G4DDK describing the latest modifications to fine tune the design of his ultra-low noise 23cm preamplifier design which uses a MGF4919G HEMT device in the input stage to achieve a remarkably low repeatable noise figure of around 0.25 dB with an associated overall gain figure around 36dB.
The mounting of the input HEMT device is unusual in that rather than the source leads being soldered directly to the PCB earth plane in order to obtain minimum inductance, the leads are raised up above the PCB with small inductances connected to ground to provide some series negative feedback which optimise the noise figure. There are also small inductances in the gate input circuit to improve the input match and in the drain lead to optimise the output match. The profile of the HEMT looks rather like a small praying mantis insect sitting on the PCB!
Sam reported some impressive repeatability statistics for noise figure varying from a minimum of 0.2dB to a maximum of 0.3dB over a sample size of 25 units. Sample measurements have been verified with NF measurements taken at various EME conferences.
More information is available on Sam’s website at www.g4ddk.com
The final paper was delivered by Brian Colemore, G3NNS who described some of the more recent weak signal modes such as WSJT and JT65 etc. now available for use via a PC and sound card for the enhancement of weak signals. These modes employ DSP techniques and waterfall displays for Troposcatter or EME or JT6M for Meteor Scatter which will reliably decode data signals many decibels below the noise floor and use multi-tone encoding with FEC or forward error correction. These methods allow decoding even when the signal is so weak that it cannot be distinguished by ear alone.
Earlier weak signal modes developed for VLF using very slow morse (QRSS) do not cope with the slowly changing propagation effects experienced such as with EME or with burst-mode propagation as with meteor scatter.
The Round Table formally closed at around 17-00 and judging by the closing comments made by the departing participants, was felt to be an enjoyable and successful event.
One piece of post-meeting feedback was that unfortunately there had been major accident eastbound on the M23/M25 causing long tailbacks and several hours delay for our guests starting from almost immediately after their exit from the Club.
Fortunately for your scribe, realising that the A23 was already blocked northbound from Cheals roundabout, my driver managed to turn immediately right at the Football Stadium roundabout and went up through the town thus avoiding all the local blockage!
Note: the date for the 2011 Roundtable has already been provisionally set for Sunday 11th Sept 2011- Put it in your Diary.
73, de G3GRO
Friday, January 14, 2011
CARC PROGRAMME SECRETARY
I feel privileged to have been the CARC Programme Secretary for the past eight years, however I feel that with the start of the new year and a forthcoming AGM that it is time for a fresh pair of eyes and ears, and a fresh brain to take over.
Anyone who is interested should be prepared to keep a close eye on what speakers are doing the rounds locally (Radcom and other club’s newsletters are good sources), in order to contact them by email or phone. To increase the chances of netting a new speaker you need to be planning ahead by several months so as to give room for manoeuvre on both sides. I have had success with speakers in the Sussex, Surrey, Kent, Hants and London areas, and occasionally further afield. And not forgetting that we have some excellent home-grown speakers from within the club, so there is a need to know who is doing what among our esteemed membership.
Another objective is trying to achieve a balanced programme of events, so a timetable of technical based and operating or Dxpedition type talks seems a good mix. I have always tried - not always with success - to have the event timetable running 3-5 months in advance.
Each month the RSGB needs to be notified of future speakers or events so that it can be published in Radcom and given out over the air in their weekly news broadcasts. This helps us to attract visitors, and very important, potentially new members for CARC.
A prompt email or letter of thanks to a speaker after a meeting is an important final courtesy, and furthermore helps your case if you need them to come back in a year or so’s time.
The above may sound quite demanding but in fact it is not difficult or too arduous and it is fun to do. You will also have the satisfaction of knowing that you have contributed in a major way to the successful operation of our great club and the satisfaction of your fellow members.
So, if you are interested in taking over as CARC Programme Secretary please put your name forward for nomination, ideally before the forthcoming Annual General Meeting on 26th January. If you are potentially interested but need more information please don’t hesitate to give me a call on 01342 714402 or email me at
John Longhurst G3VLH
Programme Secretary 2002-2010
Crawley Amateur Radio Club
Tuesday, January 4, 2011
News of Others
Hon. President, Derek G3GRO reports exchange of greetings over the festive season with long-term CARC DX members Ron, VK6RV in Perth WA; Peter,VA3PJ in Ottawa; Ray, G3LNM near Norwich; and Ken, G3JKF in Seaford who all send their best wishes to the Club.
Ray and Ken both said that they look forward to reading the CARC on-line Newsletter and keeping track of what we had been up to.
Ken reported that he has like several of us more locally, been experimenting with WSPR and has been getting kitted up to carry out some serious comparison of an OCF wire antenna (160m to 10m) and small loops. (sounds familiar!)
Peter in Ottawa has never managed to get up his antenna tower since he moved QTH but has acquired a TS2000 and is QRV on VHF and has a built a transverter for the 900Mhz band available in Canada and the US. - Peter had been very active on 432and 1296Mhz from his previous site nearer in to Stittsville.
Ron and Eileen have unfortunately both been experiencing serious health problems and Ron, like your scribe, is not very mobile these days as a result of an infection picked up after a knee replacement operation!! He reports that he now has a poor site and like many of us he had been experiencing increasing local noise levels. He had been more or less QRT but has recently acquired an Icom IC7600 transceiver and due largely to its impressive digital noise suppression capability has recently had his first QSO on 20m in 6 years.
de : Derek, G3GRO
Ray and Ken both said that they look forward to reading the CARC on-line Newsletter and keeping track of what we had been up to.
Ken reported that he has like several of us more locally, been experimenting with WSPR and has been getting kitted up to carry out some serious comparison of an OCF wire antenna (160m to 10m) and small loops. (sounds familiar!)
Peter in Ottawa has never managed to get up his antenna tower since he moved QTH but has acquired a TS2000 and is QRV on VHF and has a built a transverter for the 900Mhz band available in Canada and the US. - Peter had been very active on 432and 1296Mhz from his previous site nearer in to Stittsville.
Ron and Eileen have unfortunately both been experiencing serious health problems and Ron, like your scribe, is not very mobile these days as a result of an infection picked up after a knee replacement operation!! He reports that he now has a poor site and like many of us he had been experiencing increasing local noise levels. He had been more or less QRT but has recently acquired an Icom IC7600 transceiver and due largely to its impressive digital noise suppression capability has recently had his first QSO on 20m in 6 years.
de : Derek, G3GRO
Monday, January 3, 2011
Single Cell Ni-MH Amp-hour Measurement
Cells are subjected to a measured discharge to find out their storage capacity.This can be done by discharging at a constant current and measuring the time it takes for the cell voltage to fall to what is deemed to be end-of-useful voltage, such as 0.9V for a Ni-MH cell.Time multiplied by the amps, or by mA, provides the AH or mAH figure.
A constant current discharge can be arranged electronically, as can the voltage monitoring which stops the clock when the end voltage is reached.Such circuits can be completed with an 8-pin dual op-amp type LM358NS and a few other components.
The measurement of capacity is often based on a 10-hour discharge rate.To increase the discharge current further will usually result in less recovered capacity.
Time indication could employ a digital display and a small processor, such as a PIC, but there is a fair amount of time needed for the software development and the construction.I side stepped that by using a small AA powered clock. The battery was removed and it was powered from the voltage monitor so as to stop when the end voltage was reached.
Such an analogue display is less than ideal because of the limitations of the 12 hour display.That is unlikely to be a problem when testing AAA cells, using a discharge current of 100mA, which were the main interest here.
The discharge current could be increased to avoid exceeding 12 hours with larger cells, but also the circuit could include a small xtal counter to light an LED after 12 hours so as to extend the unambiguous time period to 24 hours. Something for later, perhaps.
The Ni-MH AAA cell has seen a big increase in its capacity over recent years and it is now in much use in small equipments like phones and radio earphones.That was what inspired this design.
The two main elements of the present design are firstly the cell voltage monitor that provides the clock supply and secondly the constant current discharge circuit.
A basic cell voltage monitor is shown in figure 1. It operates as a comparator.The end-voltage indication level is set by VR1 and is supplied to pin 2 .The actual cell voltage Vb is applied to pin 3.While pin 3 voltage exceeds pin 2 voltage the output of the LM358 at pin 1 is a high of typically 5.4 volts.That voltage is used both to light a green LED and to provide about 1.5 volts for the clock.
The other half of the LM358 is used to control the FET current discharge, figure 2. A small resistor, R5, in the FET source produces a voltage proportional to current flow.That voltage is compared with the voltage set by VR2 and the output of the comparator drives the FET gate to make those two voltages equal.
The complete circuit is shown in Fig. 3 and uses only about 14 mA from a nominal 12 volt supply.An adequately stabilized working voltage of 6.8V for the circuit is provided by a simple 6V8 Zener diode.Text on the diagram indicates settings.
The battery voltage monitor is substantially as previously described, except for some positive feedback that uses R4 and R1 to add 50mV to the battery voltage via feedback from the high output so as to ensure a clean snap-off action when the battery voltage falls to 0.9V. If you use the voltage at pin 2 to set up a correct working, that voltage is set 50mV higher than the 0.9V battery voltage.
With the battery voltage above the minimum, IC1 output at pin 1 is typically +5.4V and is used to turn on the green LED D2. It also supplies the 1.5 volt, or so, clock supply that is derived across the 3 forward biased diodes D4, D5 and D6.The 220uF, across those diodes, provides sufficient impulse power for the clock pulses that occur each second and enables the clock supply to need only 1mA current feed to the diodes via R12.
A red LED is used to indicate the circuit is powered
Battery discharge
The battery is discharged by a V10LNF FET, Q1.In its source is the 3.3 ohms resistor R5 and with a 100mA flowing it has 330mV across it.That voltage is fed to pin 6 via R7 but, due to the current via R14 flowing through R7, another 50mV is added to the 330mV, for reasons to be explained later.
The FET current flow is set by VR2 which varies the voltage on pin 5 and so determines the FET gate bias.If the setting is made while monitoring the voltage at pin 5, that should be set to 50mV more than the wanted voltage across R5. But you can also just set for a 100mA discharge by the voltage across R5 being 330mV whilst discharging a cell.
There are two options for connecting the upper end of R9.Link 1 connects it to the 6V8 zener supply. Link 2 connects it to the output voltage provided by pin 1 of the LM358.
The first option sets the discharge current to continue indefinitely after the clock stops when the cell voltage falls to 0.9V -- or whatever other end point you care to set.
The second option causes the discharge to depend on whether the cell voltage is above 0.9V when pin1 output voltage will be high (5.4 volts).It was the reason that 50mV was added to pin 6 so that IC2 would turn the FET off properly.
However, in practice, when the discharge current is switched off the cell voltage recovers somewhat and the voltage rises up by more than 50mV such that the battery has a 100mA discharge again for a short period.That process repeats at a frequency that has been found to vary from about once every 3 seconds to as quick as 10 times per second, depending on how a particular battery recovers.Even if you increase the 50mV to 100mV it still happens, but at a lower frequency.
Mostly the clock either does not run during that oscillation or, if it does, the time increases by only a few minutes.The mode, as yet, is somewhat experimental.
I used it when I wanted to obtain a battery shortly after it had reached its 0.9V level, to see what a cheap, red/green, battery tester would indicate.
FET suitability
In order that the FET will maintain the 100mA discharge down to a cell voltage of 0.9V, the discharge loop resistance, which includes R5, must be sufficiently low and R5 was restricted to 3.3 ohms.More resistance is in the FET.According to the data sheet the FET has a typical resistance of 4 ohms with a maximum of 7 ohms.Thus a typical loop resistance will be 7.3 ohms total needing a cell voltage of not less than 0.73V.Which is OK for our 0.9V minimum.
However, a 7 ohms FET will require 1.03 volts and is not OK.
There is a choice here in what to do. Either use two FETs in parallel as one, which will always be OK for 100mA,or riskhaving to change the FET. If you want to be economical, make a circuit to take two, use one to start with and test it.
FET Test
The FET test is fairly simple to do.First set up the pre-sets to discharge a fully charged cell (1.2 volts or so) at 100mA and then remove the cell and apply just above the minimum 0.9 volts in its place and measure the FET gate voltage to see that it is still being controlled.One of the link options switches the FET off at the 0.9V minimum.
A test like that on the prototype, using a single FET, showed a gate voltage of 3.4V with a fully charge cell which rose to 3.8V with 0.9V cell voltage.The 3.8V is healthily less than the control voltage maximum of 5.4V and so no problem is expected.
In general you should perhaps change the FET if the gate voltage needed is more than about 4.5V.
For the design to be able to discharge at 200 mA it needs more FETs in parallel and also the 3.3 ohm R5 should be reduced to half that (1.65 ohms).The pre-set settings will be much the same as now.You could have two FETs each using 3.3 ohms, and switch the second gate on for the higher current.But be careful not to damage the gate which is static sensitive.
=========================
Why anLM35
The LM358 has inputs that go down to zero volts and so it is able to monitor the 330 mV across the 3.3 ohm.Its output voltage ranges between 0.7V and 5.4V when powered with the 6V8 supply voltage.
The output will actually go down to 0V but it is not practical to use that because even 1mA was found to cause an 0.7V minimum.
Test Results
So far 12 Ni-MH cells have been tested.A 500mAH cell taken from each of two 4 year old house phones lasted just 10 minutes.Several 2 year old900mAH cells that had seen small use showed only 600mAH.More recent versions of those cells by the same manufacturer, with the same type number, but having a different colour sleeve, and now claiming 850mAH, returned figures of 800mAH.Had I discharged them at 85mA quite possibly they would have produced the claimed 850 figure.
Ken Holford (G1ACH)
A constant current discharge can be arranged electronically, as can the voltage monitoring which stops the clock when the end voltage is reached.Such circuits can be completed with an 8-pin dual op-amp type LM358NS and a few other components.
The measurement of capacity is often based on a 10-hour discharge rate.To increase the discharge current further will usually result in less recovered capacity.
Time indication could employ a digital display and a small processor, such as a PIC, but there is a fair amount of time needed for the software development and the construction.I side stepped that by using a small AA powered clock. The battery was removed and it was powered from the voltage monitor so as to stop when the end voltage was reached.
Such an analogue display is less than ideal because of the limitations of the 12 hour display.That is unlikely to be a problem when testing AAA cells, using a discharge current of 100mA, which were the main interest here.
The discharge current could be increased to avoid exceeding 12 hours with larger cells, but also the circuit could include a small xtal counter to light an LED after 12 hours so as to extend the unambiguous time period to 24 hours. Something for later, perhaps.
The Ni-MH AAA cell has seen a big increase in its capacity over recent years and it is now in much use in small equipments like phones and radio earphones.That was what inspired this design.
The two main elements of the present design are firstly the cell voltage monitor that provides the clock supply and secondly the constant current discharge circuit.
A basic cell voltage monitor is shown in figure 1. It operates as a comparator.The end-voltage indication level is set by VR1 and is supplied to pin 2 .The actual cell voltage Vb is applied to pin 3.While pin 3 voltage exceeds pin 2 voltage the output of the LM358 at pin 1 is a high of typically 5.4 volts.That voltage is used both to light a green LED and to provide about 1.5 volts for the clock.
The other half of the LM358 is used to control the FET current discharge, figure 2. A small resistor, R5, in the FET source produces a voltage proportional to current flow.That voltage is compared with the voltage set by VR2 and the output of the comparator drives the FET gate to make those two voltages equal.
The complete circuit is shown in Fig. 3 and uses only about 14 mA from a nominal 12 volt supply.An adequately stabilized working voltage of 6.8V for the circuit is provided by a simple 6V8 Zener diode.Text on the diagram indicates settings.
The battery voltage monitor is substantially as previously described, except for some positive feedback that uses R4 and R1 to add 50mV to the battery voltage via feedback from the high output so as to ensure a clean snap-off action when the battery voltage falls to 0.9V. If you use the voltage at pin 2 to set up a correct working, that voltage is set 50mV higher than the 0.9V battery voltage.
With the battery voltage above the minimum, IC1 output at pin 1 is typically +5.4V and is used to turn on the green LED D2. It also supplies the 1.5 volt, or so, clock supply that is derived across the 3 forward biased diodes D4, D5 and D6.The 220uF, across those diodes, provides sufficient impulse power for the clock pulses that occur each second and enables the clock supply to need only 1mA current feed to the diodes via R12.
A red LED is used to indicate the circuit is powered
Battery discharge
The battery is discharged by a V10LNF FET, Q1.In its source is the 3.3 ohms resistor R5 and with a 100mA flowing it has 330mV across it.That voltage is fed to pin 6 via R7 but, due to the current via R14 flowing through R7, another 50mV is added to the 330mV, for reasons to be explained later.
The FET current flow is set by VR2 which varies the voltage on pin 5 and so determines the FET gate bias.If the setting is made while monitoring the voltage at pin 5, that should be set to 50mV more than the wanted voltage across R5. But you can also just set for a 100mA discharge by the voltage across R5 being 330mV whilst discharging a cell.
There are two options for connecting the upper end of R9.Link 1 connects it to the 6V8 zener supply. Link 2 connects it to the output voltage provided by pin 1 of the LM358.
The first option sets the discharge current to continue indefinitely after the clock stops when the cell voltage falls to 0.9V -- or whatever other end point you care to set.
The second option causes the discharge to depend on whether the cell voltage is above 0.9V when pin1 output voltage will be high (5.4 volts).It was the reason that 50mV was added to pin 6 so that IC2 would turn the FET off properly.
However, in practice, when the discharge current is switched off the cell voltage recovers somewhat and the voltage rises up by more than 50mV such that the battery has a 100mA discharge again for a short period.That process repeats at a frequency that has been found to vary from about once every 3 seconds to as quick as 10 times per second, depending on how a particular battery recovers.Even if you increase the 50mV to 100mV it still happens, but at a lower frequency.
Mostly the clock either does not run during that oscillation or, if it does, the time increases by only a few minutes.The mode, as yet, is somewhat experimental.
I used it when I wanted to obtain a battery shortly after it had reached its 0.9V level, to see what a cheap, red/green, battery tester would indicate.
FET suitability
In order that the FET will maintain the 100mA discharge down to a cell voltage of 0.9V, the discharge loop resistance, which includes R5, must be sufficiently low and R5 was restricted to 3.3 ohms.More resistance is in the FET.According to the data sheet the FET has a typical resistance of 4 ohms with a maximum of 7 ohms.Thus a typical loop resistance will be 7.3 ohms total needing a cell voltage of not less than 0.73V.Which is OK for our 0.9V minimum.
However, a 7 ohms FET will require 1.03 volts and is not OK.
There is a choice here in what to do. Either use two FETs in parallel as one, which will always be OK for 100mA,or riskhaving to change the FET. If you want to be economical, make a circuit to take two, use one to start with and test it.
FET Test
The FET test is fairly simple to do.First set up the pre-sets to discharge a fully charged cell (1.2 volts or so) at 100mA and then remove the cell and apply just above the minimum 0.9 volts in its place and measure the FET gate voltage to see that it is still being controlled.One of the link options switches the FET off at the 0.9V minimum.
A test like that on the prototype, using a single FET, showed a gate voltage of 3.4V with a fully charge cell which rose to 3.8V with 0.9V cell voltage.The 3.8V is healthily less than the control voltage maximum of 5.4V and so no problem is expected.
In general you should perhaps change the FET if the gate voltage needed is more than about 4.5V.
For the design to be able to discharge at 200 mA it needs more FETs in parallel and also the 3.3 ohm R5 should be reduced to half that (1.65 ohms).The pre-set settings will be much the same as now.You could have two FETs each using 3.3 ohms, and switch the second gate on for the higher current.But be careful not to damage the gate which is static sensitive.
=========================
Why anLM35
The LM358 has inputs that go down to zero volts and so it is able to monitor the 330 mV across the 3.3 ohm.Its output voltage ranges between 0.7V and 5.4V when powered with the 6V8 supply voltage.
The output will actually go down to 0V but it is not practical to use that because even 1mA was found to cause an 0.7V minimum.
Test Results
So far 12 Ni-MH cells have been tested.A 500mAH cell taken from each of two 4 year old house phones lasted just 10 minutes.Several 2 year old900mAH cells that had seen small use showed only 600mAH.More recent versions of those cells by the same manufacturer, with the same type number, but having a different colour sleeve, and now claiming 850mAH, returned figures of 800mAH.Had I discharged them at 85mA quite possibly they would have produced the claimed 850 figure.
Ken Holford (G1ACH)
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