2013 John Moyle Field Day

Hi all,

The John Moyle Field Day is a Amateur Radio contest conducted once a year. It, along with the VHF/UHF field days represent the four major line of sight frequencies based contests in Australia. The John Moyle field days (JMFD) also have a substantial HF component that is not present at all on the VHF/UHF field days, and while it also allows activity right into the mm bands, typically operators are exiting stage left at 23cm or 13cm.

It’s a good contest for backpack portable because of the 6 hour section. It also rewards repeat contacts on CW and Digital modes, unlike the VHF/UHF field days. I am finding that I am able to operate chasing contacts nearly the whole 6 hours rather than lots of CQ’ing.

Mt Torbreck VK3/VN-001

Last year I participated in the JMFD from here, and I decided to do the same again this year. Mt Torbreck is the closest 10 point SOTA summit to Melbourne. It has no commercial radio equipment on the summit and is not accessible by road. There is only slight obstruction into Melbourne, so with a reasonable antenna, one can work HT stations on 2 and 70cm. The JMFD has a distance component, and Mt Torbreck is a good distance away to get many Melbourne contacts into the higher point distance bands. A number of JMFD stations also head southwest and west from Melbourne for the field day and this means that those contacts are high value. The EMDRC normally activate Mt Cowley as VK3ER for this contest and Mt Torbreck has LOS to Mt Cowley, about 222km away. Incidentially Mt Cowley is VK3/VC-022, but VK3ER drive to the top and use generators for their high powered station, so they are not a SOTA contact.

Mt Torbreck is accessible by a 2km walking track which climbs about 300m from the car park to the west of the summit. The walking track is steep and good shoes or boots are a plus. It takes about 50 minutes to climb up and 40 back + extra if carrying a lot of weight. I was carrying a lot of weight on this trip.

Equipment

I normally plan to make two trips up because I have too much stuff for one trip. The stuff to be carried up includes:

  • Yeasu FT-897 all mode rig
  • Yeasu FT-817 all mode QRP rig
  • 2 squid poles for a 2m and 70cm colinear antennas
  • 6 1.5m al segments to make 3 times 3 metre poles for various antennas
  • A turnstile antenna for 6m. This uses four 72cm M10 al segments with M8 taps to screw in 4 more 75cm segments to form two dipoles that are perpendicular horizontal polorization. There is an effective ugly balun for 6m near the feedpoint with a female UHF connector
  • A quadruple quad antenna for 2m, which comprises of 10 al segments. There are two fiberglass poles about 50cm long to mount at the bottom and the top. This goes through a 2 PVC pipes that join together so that they are just over 2m long. This is mounted on the pole by a small al segment to offset it, and a bit of sticky tape to provide a shunt to ensure that the PVC remains vertical
  • A similar setup on 70cm but here I have two quadruple quads
  • 12 Turngy 3S 5000mAh LiPos. I put 3 in parallel x 2 in series when using them, so I effectively have two rounds of this
  • A 12V down DC-DC converter sitting on the output of the LiPo array
  • 3 Turngy 3S 2.2mAh LiPo packs to power the computer for a while
  • A laptop with a supply that takes a 12V input
  • 12 18650 lithum ion cells in 4 lots of 3 in series. Each one can be used to power the FT-817 for a while – my typical SOTA power setup
  • A pile of Anderson Pole terminated power cables, including four 1 to 3 Y cables
  • A collection of LMR195 and LMR400 cables. The 195 cables have either BNC or UHF connectors. The LMR400 are all N connectors. I also brought up a pile of converters. I typically use UHF on 6m and BNC/N on 2 and 70. The FT-897 has a UHF connector for HF/6 and an N connector for 2/70. The FT-817 has a UHF and a BNC connector which can be configured through the menus
  • A one man tent to keep me out of the sun and the forecast showers
  • A MiniVNAPRO and the extender to do some tests on the antennas to ensure all is ok
  • Some plyers, shifters and other misc equipment to do any small repairs to equipment if that proves necessary
  • A collection of HT radios for 2 and 70. The idea being to use these for FM on 2 and 70 for at least some of the contacts to save power
  • Some headphones
  • A CW touchkeyer
  • A Signalink USB for digital modes, plus my Phone/Digital interface for a backup if required

For those who follow my SOTA activations, you would realise that this is far more than I normally take. You may realise why two trips are needed. Practically this means walking UP then DOWN then UP the mountain before the start of the contest, then DOWN then UP then DOWN at the end.

The setup

Upon arrival after the first accent, I put up the tent and piled the stuff in. Carrying all that LMR400 cable, the FT-897 and the 12 LiPOs certainly was a lot of weight and it took 1:10 to get up. I headed back down and got the remainder of the stuff, and it took 40 min down and 50 min up. First was getting the squid poles up. My 2m colinear has seen a lot of SOTA action, and a little stub I made up for 144.1 works well. Very low SWR – nice one. I use it without the stub on 146.5, with SWR around 2. With the stub for 144.1, 146.5 has a SWR around 3.

The 70cm colinear is short, with the good oil around 455MHz. I planned a stub for this to get 439 at least in the game, but I was not successful. There will be more about this in another blog post in the future, but for now I could not effectively use this colinear – what a shame because this was going to be the main game on 70cm vertical. I put up one of my whip antennas on the squid pole about half way up and fed it LMR400 cable back to the radio.

Next up was the 6m turnstile. This is pretty quick to put up. This is not a gain antenna, but it is enough to put me in the game on 6m and it can break up quickly to go in a pack. It gives an SWR below 1.5 at both 50.15 and 52.15

Here’s a pic of the 6m antenna in the foreground with the two squidpoles in the background, plus the operating tent. You can see the trig point to the right in the trees:

Operating location at Mt Torbreck with a 6m turnstile, plus 2 & 70cm colinears on squid poles

6m turnstile, plus 2 & 70cm colinears

The 2m quadruple quad was next. Last year I had two of these in an array, but they were too phyisically heavy to put up, so I jury-rigged up one. This year I did not bother with an array, just going for one with some work to mount it more effectively. There’s a pic below. It was well below 1.5 SWR at 144.1 and around 1.7 at 146.5.

2m quadruple quad at Mt Torbreck

2m quadruple quad at Mt Torbreck

I had thought of trying a longer pole but I would need to use stronger materials. Another idea is to mount it on a squid pole. I’ll think about this for next year, but this will be asking a lot more of the squid pole than a wire inverted V, end fed or a vertical on HF. Why a quadruple quad? Because it is roughly equivalent to a 15 element yagi, especially if I can get it off the ground a bit more.

Finally it was the 70cm quad-quad array. Here’s the pic:

Array of 70cm quadruple quads on Mt Torbreck

Array of 70cm quadruple quads

One of the quads didn’t work so well, and time was running short, so I simply used the other one. Their feedpoint impedance is reported low at about 25 ohms. I’ll need to look into this some more, but I wanted to get operating at around 1:30 to 1:45pm so off I went.

The contest

It started lightly raining about 12pm, so I was a little reluctant to keep the MiniVNAPRO out in the elements. A few mad dashes and doing some analysis on the computer. My plan with the computer was to run it on the three 2.2Ah LiPOs directly until they were flat and then run it on the main supply for an hour. I could then run the computer on its own batteries for the rest of the time without them running out by the end. This worked well, but the 2.2Ah LiPOs gave me more time than expected. Nice to get more than you expect! When the LiPO monitors were reporting individual cells on the 2.2Ah batteries down to 3.55V, I pulled the computer out.

The whole 6 hours of operating was quite fast and furious. Most of the action was on phone, but VK3ER had a digital setup, at least on 6 and 2. They also had CW on 6/20/70 so there was some good triple dipping. I used Fldigi for PSK, and was more comfortable using it in the end in my one man tent lying on my side trying to type on a computer with the pouring rain outside than what I was in the middle.

I was also glad I brought the headphones, because the rain was very loud in that small tent. During the worst periods, I would mainly use the vertical antennas, which the main gun was the 2m colinear. The little whip at the end of the LMR400 cable on 70 was just no match for the 2m colinear. I need to get that 70cm colinear going for next year, these babies are just too good to ignore. The colinear being omnidirectional on the horizontal plane was good during the pouring rain because I did not need to get out of the tent to adjust anything. Same goes for the 6m turnstile (although it’s not a gain antenna). Gain on 6m might be a little hard to do given it needs to fit in a backpack along with everything else.

There was a 2 hour sunny period during the middle of the contest. This allowed me to get a bit more relaxed and I made more use of the quadruple quads. Towards the end it was raining again, but I really wanted some nice juicy contacts north into VK2, and my 2m q-quad was able to get them.

As for power, I already mentioned that the 2.2Ah LiPOs powered the computer well. I ended up not even using half of the 5Ah LiPOs, the first set of 6 were only 80% used at the end, with cell voltages around 3.75V. The “knee” on these is at 3.65V where the voltages start to fall away more quickly. I was hammering away with FM at 50 watts on 2m, but the LiPOs and the 12V regulator powering everything were stone cold. Not even lukewarm. This was a contrast to last year because my old 100 array of 18650 cells could not handle it. The LiPOs are just so much better for this usage.

Come 7:30pm it was finish time. I ended up not even turning on the HT’s. I barely used the FT-817, which is a major change from last year, where because of power constraints, I made most FM contacts on the HTs, and used the FT-817 for a fair amount of the rest. This year, the FT-897 was used for every scoring QSO. Did I mention that half of my big LiPO’s were not even touched? đŸ™‚ I just had to make sure that at least 4 QSOs were at 5 watts so I could keep my QRP SOTA activator’s endorsement intact.

Packing up

So contest finished, and it was time to go home. Too much stuff there to just leave it – although the thought did cross my mind as to what would happen if I just walked down the mountain with all that stuff still up there! It was raining again and it took about an hour to pull down all the antennas. With all the wet conditions, I needed to be careful getting the fragile computer back down the mountain, so I thought I’ll go easy on the weight on the first trip, but still enough to hopefully not have a tonne of weight on the second. One thing I’ll need to make sure of next time is to split up some of the LMR400 cable on the trips because this stuff is heavy.

I left on the first trip down at 8:30, left the car to go back up at 9:20, packed up the tent and did my final checks to make sure nothing was being left and departed Mt Torbreck at 10:20pm for the last time. I arrived at the car at 11:15. It was slow the last time with the heavy pack and the slippy wet conditions on the way down. At least it had stopped raining. I was very tired for the drive home and needed a 15 min powernap in Healesville to keep things safe. My wife thinks arriving home at 2:30am is crazy but it was a very good day with 92 contacts and over 1440 JMFD points.

Regards, 73, Wayne VK3WAM

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Activation of Point Nepean NP

Hi all,

This is a quick post about my Keith Roget Memorial National Parks Award activation down at Point Nepean National Park. I set up near Observation Point, about 500m from the Gunners Range car park. I worked: vk3pf/p, vk3hra/p, vk3up, vk3azz, vk3fd, vk3asd, vk3hy, Vk7or/2, vk3byd/p, vk3afw, vk2agr. The last three were on CW, the rest on SSB. vk3afw was a suprising CW contact on 20m, but all the rest were on 40m.

One little nice bonus was vk3byd/p on vk3/ve-004, which is in the Alpine National Park. While it was not a SOTA activation for me, it was nice to at least chase SOTA, especially on CW. I have not yet been bold enough to do a SOTA activation relying only on CW, the SSB mic has always been there!

I also had another try at PSK31, but there were no takers. I am aware that I have a bit of splatter myself, it looks like the audio input levels on the FT-817 need to be lower than the FT-897.

I’ve updated my Keith Roget map. While VK3PF, VK3ZPF, VK3VTH and likely even VK3HRA are well ahead of me, I still intend to eventually activate all 45 parks over time.

Regards, Wayne Merry VK3WAM

Three summits before the rain

Hi all,

It’s taken a few days to put this posting up, but it is always nice to revisit activations.

VK3/VW-013 West of England Range

I was up in Ballarat staying with the inlaws for most of the Melbourne Cup long weekend. I have generally taken advantage of getting away during one of the days of these trips to get a few activations, and there are many SOTA summits within a reasonable driving distance of Ballarat to choose from. At this stage I have not yet activated them all, so I can add to my SOTA uniques count. It will be interesting to see what happens after Jan 1 when points for previously activated summits become available for activators again.

The West of England Range is a north south range which is mostly protected by the St Arnaud Range National Park. It is at the northern end of the Victorian Pyrenees. This range is named after the Pyrenees in France/Spain/Andorra for some supposed likeness that I have yet failed to see…..

Anyway, there is a 4WD track that heads north south along the range. Parts are 2WD. I accessed the summit from Redbank using the Barkly-Redbank Rd which is quite passable in a 2WD. I turned onto Centre Rd, but could only go about 100m before needing to park the car and continue on foot. There was about 200m of overall climbing, counting a few ups and downs to continue north along Centre Rd to get to the summit. Here is a look near the operating location:
Near operating location at VK3/VW-013

During operation, I had a 4WD go past, plus some dirt bikes. Conditions were actually quite poor, but I did not have too much difficulty getting the required contacts. It was getting gloomy and a sharp rain shower started, so it was time to pack up. On the way back to the car, a convey of 10 4WD vehicles went by. Obviously a popular spot.

VK3/VW-016 West of England Fire Tower

After heading back to Redbank, I headed up to Stewart Mill and used Teddington Rd to access Centre Rd again, south of the summit. Centre Rd is still quite rough for a 2WD, but I was able to get about half way to the summit, and walked the rest. I was a little closer than what I was at VK3/VW-013 earlier in the day. I operated about 50m NW from the fire tower:
West of England fire tower

Here is the operating gear:
Operating location at West of England fire tower

I had line of sight to the Grampians from here and Allen VK3HRA was activating VK3/VW-002. He was armchair copy with a HT on 146.5FM. Conditions on 40m had improved significantly from what they were at VK3/VW-013, aside from S7 QRN from a noise floor around S1, S2.

I also gave my phone radio interface a go on both 40m and 20m while I was here. It seems to work well on 40m, but it is having a little difficulty holding the PTT open on 20m. Interesting that it is band dependent. My tests on 2m at home showed no problems. I think I will change a few component values to increase the current at the base on Q2, the PTT grounding transistor. This should fix this problem.

After this, it was back to the car for a trip to Mt Moliagul for the third activation of the day. This would involve more unsealed roads, so the car was going to get dirty again.

VK3/VN-024 Mt Moliagul

After travelling for about 45 min, I arrived at the road heading up the mountain. The Google map is a little inaccurate, with the road heading up the mountain a little east of where marked on the map. After sorting this out, I headed up. The road is a little rough, but quite passable in a 2WD in dry conditions. The public road goes all the way to the top, but I parked at a flat section about 40 or so vertical metres below the top, safely out of the activation zone. From there it was just a short walk up to the top where I found a nice spot to activate:
Activating Mt Moliagul

Conditions were similar here to VK3/VW-016. Good signals, but a high level of QRN. It was also getting windy, and a change was arriving when it was time to pack up. I struggled to hold the squid pole up in the wind while I was trying to retract it. Overall, I was quite pleased with the activation, plus the two earlier with 6 SOTA points in the bag when it was time to pack up and head back down. I had one last summit to try for, Mt Bealiba VK3/VN-026, but it had started to rain. We would need to see how this one goes.

VK3/VN-026 Mt Bealiba

This summit is in a Box Ironbark forest with a very open forest floor. I used a road branching off Goldsborough Rd, which got within about 1km of the summit. There are likely 4WD tracks that go all the way up. It would only be a 15 min dash across the very open forest to get up to the top, but given the rain and my lack of wet WX gear, I thought I might give this one a pass for today. Unfinished business for another time.

With that, it was time to head back to Ballarat. 3 out of 4 is better than 2 out of 3 and Meatloaf reckons that ain’t bad.

Regards/73, Wayne

FT-817 (& FT-897) Phone Audio interface part 3

Hi all,

This is a continuation of FT-817 Phone Audio interface part 2.

It has been a while since I have posted on this topic, and the principle reason for that is that I was patiently, and then not so patiently waiting for boards that I had ordered. They arrived while I was away on a series of SOTA activations, but I have populated one of these boards and tested. Apart from getting one of the cables wrong – which I needed to fix, everything works quite well. The markings of the rectifier diodes are wrong, but I already knew that upon ordering as that is a bug in the device files in my design software.

There is quite a lot of latitude with the potentiometer settings, both audio in to the phone and audio out. I ended up using a volume level about 2/3rds on the phone. There is going to need to be individual adjustment of these, as it is a function of the phone used, the digital mic setting on the radio and also the need to ensure that the signal is not being splattered. If you do not have access to two radios with one having an existing audio interface – eg a Signalink for testing, then you will require some on air reports to ensure that your audio is at a good level without causing splatter.

Here is a pic of both an unpopulated board and a populated board. For an Samsung Galaxy S2, I used a 12K resistor for R10. Apple devices might need a lower value, around 4.7K to raise the current that the interface draws. It seems like around 600uA is the threshold for Apple devices, but the Galaxy S2 is happy around 300uA.

FT-817 to phone interface

Populating the board is quite straightforward. Although most components are surface mount, they are either 1206 or 0805 size, and I did not even need to use a magnifying glass. I recommend using a temperature controlled iron with a fine tip.

I have a few spare boards, and can make these available for $12, or $25 with the parts, either $A or $US plus postage. Send me an email at vk3wam@gmail.com if you are interested.

It should be possible to adapt these boards for use with other radios as the connectors at each end are straight inline. On the phone side, most modern devices have ground on pin 3 and mic on pin 4, but many older non-Apple devices are the other way around, ground on pin 4, mic on pin 3. If you have such a device, then you’ll need to wire it that way. On the radio side, RX audio (phone in) TX audio, GND and a PTT grounded to TX signals are required and most radios should support these. The Yaesu radios provide a constant audio input on their data port, but some radios (I believe the Elecraft KX3 falls into this category) will change the output audio based on the AF gain (volume) setting.

73 de Wayne VK3WAM

Designing a 20/40 band CW rig – Part 2

Hi all,

This is a continuation of Designing a 20/40 band CW rig – Part 1.

Shown below is a schematic of the TX and initial RX parts of the rig. I have been successful in simulating all of these parts, and have a reasonable amount of flexibility if the real world performance of the components does not match the simulated performance.

Schematic of the TX and initial receive sections of the rig

TX Driving

This being a CW orientated rig, all that is needed is a oscillation on the desired TX frequency. CW merely turns it on and off. I did mention that I wanted to retain cabability of PSK and FSK modes. PSK needs the phase of the oscillation to be changeable, while FSK modes need the frequency to be changeable. An Analog Device AD9834 fits the bill. Steve KD1JV is using this in his Mountain Topper. This device is not a PLL and VCO combination, rather it generates the output digitally, and then feeds a DA convertor to generate the waveform. The output is needed for two things – it is the Local Oscillator for a mixer, and can be used directly for a TX frequency. The AD9834 has a number of capabilities that I plan to use, but this will be for another post.

Unlike Steve, I have decided to take the analog output of the AD9834. This output will drive the initial mixer, and the device selected has a 50ohm load. I’ll talk about this device on another post, but I will be using a different approach to the other designs I have seen because I want more dynamic range and better inter-modulation distortion performance.

The input to my driver is going to be taken off this output. The AD9834 can provide a balanced or unbalanced output. I need unbalanced. This signal is shown as OSC. It then feeds the base of a MMBR941, Q1. This is a RF BJT device in common emittor configuration. One of the nice aspects of BJT devices in common emitter is there is a fair degree of flexibility in setting the input impedance and the output impedance of the device. I decided on a 150ohm input impedance. I am also driving the device fairly hard, but not too close to device limits. The gain on the device is 26dB.

To save power when not TXing, I use Q2 as a switch. This 4401 device is being used as a current sink, switched on during TX, and off when not. It deprives Q1 of its DC ground, so no DC current will flow through the device. The bias network is shut down, but is still kept alive on AC so that the load presented to the AD9834 is not significantly changed. The effect of Q2 kills nearly all of the output power from the collector of Q1.

TX Power

My objective is to deliver 5W into a 50ohm load (antenna). There are quite a lot of choices to go about this, but I want to keep things as simple and as cheap as possible. I considered initially using another BJT in emitter follower mode, by using Q1 to deliver the desired peak to peak voltage AC signal and then the emittor follower would supply the current. I used an inductor on the emitter to improve the efficiency, but at the end of the day, it is still being used in Class A mode. This is a CW rig, so Class C amplifiers await!

The schematic shows three BS170s that are driven by the output of Q1 on their gates. These are N-channel MOSFETs that can dissipate about 800mW of power. If they are run 66% efficient, then that means that each one can deliver 1.6 watts. The efficiency is a function of the peak to peak voltage supplied by the MMR941, and what level the bias is set at. The bias mid point needs to be below the pinch off voltage on the BS170’s for Class C operation. The further away, the better the efficiency, but it cannot be set too far away, as there are limits to the peak to peak output I can get from the driving device. After a fair amount of experimentation, I set the bias level using a voltage divider resistor network. R9 and R10 (the R10 going to ground) form this network. (The other R10 nearby on the base of Q3 has a new identity as R18). This level ends up being around 1.2V, around a volt below the BS170 cutoff to ensure Class C operation.

The job of Q3 is to act as a switch, on during TX, so that R9 and R10 do their job as described. Off during RX, so R9 is taken out of the circuit, and R10 pulls the base of the BS170’s to ground so that they are cut off from doing anything. The BS170s then act as open circuits.

Presenting the output to the load

Class C waveforms have less than half of the initial sine wave present. The BS170s also present a changing load to Q1, so what it produces is not a great looking sine wave either. We actually have quite an ugly looking waveform on the output of the BS170s. This needs to be cleaned up. Also, the load is not 50 ohms. It can’t be if this circuit is going to operate off 12V. The best that can be hoped for, in terms of an output wave form is 24V peak to peak, due to the action of the inductor L2. I used the complex model of L2 in my simulators, rather than using a perfect inductor. The complex model output was practically indistinguishable from the ideal model. Coilcraft make some good inductors, and I plan to save builders of this rig from having to wind their own inductors, by using these Coilcraft chip inductors.

24V peak to peak really only allows for 12 ohms load impedance directly on the finals. This needs to be transformed to 50 ohms at the antenna connection. All rigs need to do this transformation. Steve’s Mountain Topper Radio provides a network for each band. The FT-817 provides one for each of its bands that it can TX on, and they are switched by relays. The FT-817 set of finals are operated in a push-pull configuration, but off a 8V rail. This means that the load impedance that these are driving will be lower than 12 ohms, perhaps about 9. I should analyse the inductor/capacitor networks for a given band that Yaesu have put in there. If you were to look at the circuit diagram, these matching networks take up most of the power board module schematic.

I reckon a bit of convenience is a good thing, so I am going to use a relay to switch between the two bands. This relay is K1. It is DPDT, so I can use the one relay for both ends of the matching network.

The match network has a LC tank which does most of the job of restoring a clean sine wave, and then a LC series, presenting a high impedance to remaining harmonics. This second LC series begins the process of impedance matching, where I only need two more capacitors to complete the job. This is per band of course.

Now reality bites, and there is the need to use real world components. Also, for these networks, X7R dialectic is not acceptable, but for cheap capacitors, 1nF or above tends to be X7R. So to get around this, I have paralleled up some caps to get the values I want, and to continue to use NP0 dialectic caps in 0805 SMT size. There was one cap where this approach was too long in the tooth, so I use a 3.3nF ATC cap that is 1111 size. It’s a much more expensive cap, but I’m only using one!

After these matching components, I have a sine wave output at 50 ohms supplied to the antenna. It is the job of the operator to take it from there.

Receiving

I have to receive as well, this is a transceiver after all! Now, approach 1 could take the signal straight off the antenna jack, but there is the matter of the TX output to deal with. At 50 ohms, this is not going to be a 20V peak to peak output any more. It is closer to 83V peak to peak. Of course, all of the caps need to have dialectics rated to 50V, as 83V gets 41.5V from ground, each side.

Now, I could use a relay to switch between RX and TX, to shut out the TX signal from going anywhere but out the antenna jack to the antenna. The FT-817 does. One problem – full break in on CW. It is not too good to have a relay clatter (twice) every time you send a dit or a dah. I want full break in capability on this rig, so this means using a transistor approach. A transistor is going to have to hold back this 83V, but that is too much.

Instead, I have taken a similar approach to Steve KD1JV, by putting a blocking circuit at the 12 ohm area. This cuts down the voltage that the blocking network needs to resist on TX. It also has the benefit of providing a filter through the same LC networks that dress the TX output for the antenna.

The main transistor to block is Q9, a N-channel MOSFET 2N7002. I have used a biasing network, that is assisted by BSS84 Q10 and a 4401 Q11.

Q11 is a current sink. When switched on, it takes the gates of both Q9 and Q10 to near ground. Q9 is a NMOSFET, so a ground on its gate will block any signal that is about 0V or higher. Near ground on Q10 is a PMOSFET, so it is switched on, there being nearly -12V between its gate and source. Q10 switched on takes R15 out of the circuit, leaving a voltage divider of R13 and R14, meaning Q9 is biased over 10V. The input signal is going to swing between 0V or so and 20V on the drain of Q9, with 0v at its gate. If something makes it to the source of Q9, it won’t be much below the gate, meaning Q9 should stay switched off, switching off TX signal from sensitive RX circuitry.

When wanting RX, Q11 is switched off. This then means the gates of Q9 and Q10 are pulled to 12V by R17. 12V on Q9 gate will tend to switch it on. Q10 will be switched off, meaning that the bias network is now R15+R13 against R14. The drain of Q9 will be biased at around 1V. There is 12V on the gate now, and around ground on the source. Q9 will be switched on as hard as I can make it, so get as much of the RX signal through.

Unfortunately, when TXing, quite a bit of the signal still makes it through Q9. Too much by itself to be safe. The transistor itself is ok, it is not being used anywhere near maximum limits, but the mixers awaiting later will not like what gets through. I want to block this signal, so I use another LC series resonant device to block the harmonics. This is because what does get through Q9 is horribly mangled with most of the power in the harmonics, not the fundamental. This cuts things down nicely. Also this network starts the process of impedance matching from 12 ohms back up to 50 as the mixer I want to use wants 50 ohms as a source impedance. Now this matching network is band specific, so this means a second relay. This relay, like the TX relay is only switched during band changes, so there will not be any relay clatter here. Q12 and Q13 are little helpers. They are switched on during TX to shunt away any TX signal that still makes it through this far, but because of the LC network, it ain’t much. The job of Q9 is also easier to block the TX signal when it is mostly high impedance sitting behind it.

Wrapping up

This about wraps up this post. Next up I will look at the audio processing part of the rig. The other major parts are the RX mixing and filtering and the microprocessor. I’ll look at these with later posts. My plan is to get one of these rigs built in about a month to two months as a prototype, and we’ll see how it goes from there.

Regards, 73, Wayne VK3WAM

This topic is continued at Designing a 20/40 band CW rig – Part 2.

FT-817 Phone Audio interface part 2

Hi all,

I have continued to work on the interface, described in Designing a Phone/Radio interface, and I think things are looking pretty good. I have changed some component values slightly to fit in with easily obtainable parts. One approach is to use thru-hole parts for everything, but this results in quite a big board. Now SMT does scare people. but if we stick to the larger part sizes, it should be easy enough. This does however means steering clear of 0402 and 0201 tiny sized components.

My first try at drawing a PCB used SMD capcitors while keeping everything else thru-hole. Using 1/4 watt thru-hole resistors ends up taking up a lot of space. I decided to change over to SMD resistors as well, but leaving the diodes, transistors and the trimmer potentiometers as thru-hole. This allowed me to get the board size at 2 inches by 1 inch. My resistors are generally 1206 size (this is .12 inches by 0.06 inches, or about 3 by 1.5mm. Most of the caps are 0805 (about 2mm by 1.2mm) size. These are reasonably easy to manage with tweezers.

People have asked what components are used for the transistors and diodes. I am using 2N4401’s for the BJTs and 1N5819 for the schottkies. Both these components should work very well.

In some of my simulations, I have tried quite “out there” scenarios. The circuit actually still works with a 1V power supply, especially with higher audio frequencies on the digital mode being used. It works with 8V, actually very well. I have not bothered higher voltages, perhaps I should give 12V a go, however no phone is going to be supplying that kind of voltage level. I suspect that they (i.e. the various phone manufacturers) are either stepping up the cell voltage output – typically a LiIon cell that will range from 4.2V down to 3.5V or so, and stepping it up to 5V, or just feeding it in unregulated, with a 5 to 10K resistor in series to current limit the supply on the microphone pin. Any of these scenarios will work with this circuit. If anything like a 3V or higher supply is involved, there will be over 50uA to drive the second transistor to sink 450uA of current on the PTT pin. Even if other radios to the FT-817 have different loads on their PTT pins, I can’t imagine it’s orders of magnitude!

On the radio side, there are clear variations. The FT-897 has a lower impedance output on the fixed audio, and a lower Vpp level. I still expect the circuit will work fine. I also had a look at the Elecraft KX3. This does not have a data port, but rather relies on the speaker output and microphone input. The speaker output will be at a higher level than what either the FT-817 or the FT-897 will drive this circuit. The trimmer potentiometer can be turned down to help. Also the radio audio control will change the voltages seen on the output. As for the input, again the potentiometer will have to be turned down, because the circuit is feeding something approaching a line level. Microphone is a good 15dB to 20dB down on that. I would presume that the KX3 would have some forgiveness about the input impedance, as cheap mics are high impedance (10K plus), while high quality mics can be as low as 100 ohs. I’ll need someone to investigate if there is any DC on the microphone input as well, as this could be there for the same reason that there is DC on the phone microphone input. If someone has a Oscilloscope and a KX3, it would be interesting to see the audio output levels, but you would also need to know what load resistor you used.

I have a picture of the circuit for you to enjoy below:

Phone Radio circuit board image

Btw, the diodes are back to front, and this is a consequence of whatever bug is in the schottky files used by GEDA. It is easier to just highlight it as an errata. The circuit will not work if the diodes are not correctly put in place.

I used the geda suite to design the circuit, using gschem to draw schematics, ngspice to do simulations, and PCB to draw the circuit art. These programs can be a little hacky and the help files are not for the uninitiated, but they certainly get the job done. I feel pretty comfortable with these, and I am now also looking to do a design for a bias tee and a preamp for 6m/2m/70cm. More about that later.

Send me an email at vk3wam (at) gmail (dot) com if you are interested in getting one of these interfaces. If people are interested, I could sell the boards at $10 US. I’ll need to look through the cost of the materials if people are interested in kits.

73 de Wayne VK3WAM

EDIT: Here is a slightly updated board design, optimised to remove some of the via holes, improve some spacing and comply with various production house design rules.
Phone to Radio interface board

Trans Tasman Contest

Saturday the 21st of June saw the Trans Tasman contest on 160m phone and 160/80m CW and digital on. It was a 6 hour contest with the best 5 hours to count.

The Eastern Mountain District Radio Club (EMDRC) was going to enter this, so I thought I would get involved doing CW and digital. I have a SignaLink USB on my FT-897 at home and so I put my hand up to focus on 80m.

Operating Station setup

I would have liked to have posted photos on this post, but I was busy contesting. Someone else took some photos, so hopefully they will show the station and I will edit this post at a future time.

My operating station consisted of my FT-897 brought in from home, a MFJ1025 noise canceller, a MFJ T-match manual tuner, a LDG ZPro-II auto tuner and the SingaLink USB. The antenna was an inverted-V full length for 80 metres. I had low SWR on the antenna without using the T-match, but found I had significantly less interference from 160m operations if I left the tuner in.

What was the ZPro doing? I had this tune a 20 metre beam for 80m to use as a noise sense antenna for the MFJ noise canceller. This seemed to work. The noise canceller was not able to lower the general noise floor, but what it was good for was getting rid of specific QRM that appeared throughout the night. The ZPro was affected by RF in the shack from 160m operations, so I had to put it in manual mode to not try to retune every time there was a 160m operation. I wonder what I was exposing myself to in the shack last night!

Anderson Poles

The EMDRC has been encouraging members to use Anderson poles There is nowhere in the shack to plug them in however, so lucky I brought a cable with rings on one end and Anderson Poles on the other. I still had to wedge these in to the power supply as it wanted lugs, but oh-well. It worked and I was able to use Anderson Poles for the rest. From the converter, I had a 3 way Y-plug, with the FT-897 plugged into this. I had a second 3 way y-plug, which was a little overkill, but plugged into this was the ZPro and the noise canceller. I could have easily plugged in 2 more things if required – so the setup is very flexible for use here at the EMDRC away from my own shack, and also for my QRO and QRP SOTA setups.

Digital observations

Digital modes that are AFSK based – i.e. all of them where a sound card is used to feed a SSB type mode on a typical rig – need the rig to stay as linear as possible. It is very important that there is no processor or ALC action. I had my rig showing ALC on its meter and increased TX level as much as possible, but not so much to activate the ALC. On the SignaLink, this ended up being around “10am” on the TX potentiometer. Other stations were transmitting with clear ALC action on their signal. This causes splatter. One station had so much splatter on their PSK31 signal that it was taking up nearly a full 1KHz for a signal that is supposed to only take 31Hz. This is multiple orders of intermodulation! I could not decode this signal – and sent them a message to turn down their TX! They did so, and while the splatter was still bad, it was at least then decode-able. A number had one order of splatter – giving a head and shoulders look. You want all of your TX energy in what is supposed to be there, and the shoulders are a waste of energy. A few stations had PSK-31 stations that had no observable splatter.

PSK31 does not tolerate almost any drift. Even on 80m there was one particular station that drifted 10Hz or so, and this was enough to cause decoding to stop until I re-clicked on the signal to move the decoding bars. This has implications for use of PSK on higher bands, especially VHF/UHF where this issue would be more critical. Some have suggested for this reason that PSK is not suitable for VHF work.

Contest Ops

In the end, I worked like a slave for the full 6 hours. My software was not that good at decoding CW, so lucky my brain can at least reasonably decode 20wpm. I operated the first 20 minutes or so of each hour CW, then the middle 20 minutes digital and the last 20 minutes CW again. The rules allowed for digital stations to be re-worked every half hour (once in the first half hour, and again in the second half hour), so I tried to take advantage of this – which mostly I was able to.

Most contest digital ops where PSK31. There was some RTTY near the start and occasionally later. One station was using Hell, but I had already worked them in that time slot. The key with Hell is to turn the software “squelch” all the way down. Hell is like reading a fax – the signal processing is in your brain.

In the end, contest activity was reasonably engaging. I found running got more contacts, so I spent about 75% of the time running. It was the first time ever that I had actually chased CW stations. This is because when I activate CW in SOTA, I am always the “running” station. I picked up the chaser caper without too much trouble. Of course in CW, one should not transmit on the running stations frequency, but offset 100Hz or so.

Having a narrow IF filter defiantly helps in both CW and digital. I would normally operate using the wide filter, but if something was happening 1KHz away that would affect the AGL, then I could quickly switch to the 300Hz Collins filter to get rid of it. The wide filter is good for seeing a broad picture on the waterfall when AGL action is not taking away the signal that I am interested in. I left the FT-897 menu on the selection where I could switch between the two filters with one press of the button.

In the end, it was an enjoyable contest. I had 87 non DUP contacts (1 DUP), so not too bad for a first effort.