Amateur Radio

Equipment Repairs

Kenwood TR751A – pot replacements

The Kenwood TR751A 25w multimode radio for 144 – 148 MHz is well regarded, with a sensitive receiver and good transmit quality. However the pots installed as dual concentric types for the AF Gain, RF Gain, Squelch and RIT functions have a reputation for failing. The manufacturer has discontinued supplying spare parts for these radios as they are now about 30 years old.

A source of replacements was identified in very similar pots stocked as spares for a Ranger CB radio at R&R Communications in the USA. This source was documented by members of the Yahoo Group for TR751 and TR851. (The group recently moved to

I ordered and received the replacement pots but had not installed them, the job waited on the back burner while I was preoccupied with other matters. With my interest in portable operations on 2m ssb/cw I realised that this radio could provide the additional power I sometimes wanted (additional over the FT817’s 5 watts) and could be a useful part of my portable operations. I am aware that the increase amounts to only 7dB but sometimes that makes the difference when using small antennas you’ve carried up to a summit and reassembled there.

After removing top and bottom covers, knobs and the front panel cover, I removed the two pots, unplugging the cables from their headers on the PCBs mounted on both pots. Desoldering the old pots from the boards was a long winded process and I found that my solder wick was not working as it should. I suspect the solder originally used has a different ratio of tin:lead and therefore needs slightly higher temperature than the 60:40 I usually use. Eventually the pots were off the boards and the new problem was to fit the replacement pots. The spacing between the three pins of the front pot section and the pins of the rear pot was quite different between old and new pots. I decided to put in small extensions for the pins of the rear pot. This was done using wire that was cut from resistors and capacitors after being soldered onto a PCB for a filter kit. Also the switch connections were different, requiring a jumper to be inserted between two pins on the PCB.

Following reassembly, the new pots appeared to protrude from the front panel much further than the originals did. I found this could be largely resolved by installing an extra nut on the control to effectively position the pot further behind the front panel. The pic following shows the result of this adjustment. A minimal amount of threaded shaft protrudes in front of the mounting panel. The limiting factor was the PCB visible here that is pushed against the assembly behind it, in fact I had to wind this pot a little bit forward because I couldn’t return the front panel assembly fully to its correct position without doing that.

Showing the two pots and their PCBs and wiring

Once back together the radio was tested ok and later I used it for a test on SSB from Black Mt, Canberra. I had a quite successful activation on 2m ssb, making contacts into Sydney (about 270 km) and to Nimmitabel (about 100km) using the TR751 and a loop antenna that had been lent to me by Andrew vk1ad. it was mounted on a short fibreglass pole.

During the testing of the radio I was pleased to see that its current drain on receive was 400 mA, which is slightly less than the FT817. On transmit full power it drew almost 6 amps. No problem for the LIFEPO4 battery normally used, which has a 20C rating, meaning it can provide 20 times its AH rating. 4.2 x 20 is 85 amps. the relatively low current drain on receive means this radio is a good option for using on battery powered activations. By comparison the IC706 or FT857 style radio would draw twice that current on receive. On transmit, the bias level of the final amplifier would double that current even before producing any RF. Turning the power level down on the higher power radio to its minimum of say 5 watts does not change that bias current, so running those higher powered radios at low power is very inefficient. It doesn’t matter if you only want 30 minutes of operation, but the same power consumed by the 706 in 30 minutes of reception would run the TR751 for at least double and possibly 4 times the 30 minutes.

Icom IC703 portable HF multimode transceiver

This rig was my primary HF rig for SOTA and parks activations. But it developed a problem in the VFO circuitry, behaving as though the dial was slipping. Turning the dial would normally result in the frequency changing continuously. However the fault was causing the frequency to freeze occasionally. I didn’t mind turning the dial a bit more but I thought that if some of the components in the encoder were faulty, maybe more would be faulty before too long and I should replace it.

I ordered the part from Icom Australia and it turned up after a predicted delay as it had been out of stock. I was told the part is used in multiple other radios including the recently released IC9700. It was reassuring to know the part was still in production.

The vfo encoder is located in the control panel for the radio. It just sends up and down signals back to the main unit. It is based on a set of LEDs and detectors, I assume light dependent resistors, arranged In a circular pattern at regular spacings around a central shaft. A circular disc with a set of holes or windows cut into it at specific positions corresponding to the LEDs allows light to pass through from the LED to the LDR. The vfo tuning direction is deduced from the timing of when light is first detected by each sensor, compared with a twin located slightly more or less than 180 degrees further around the circle. If the sequence of light detection is the sensor at 0 degrees followed by the sensor at 181 degrees, the dial must be turning clockwise so the frequency is required to move up. and vice versa when the dial is turned anti clockwise. Well, that’s how i understand it. The entire assembly is sealed into a small package looking like a potentiometer and has a cable terminated in a small plug.

The control panel for the IC 703 is very similar to that of the 706. I think it’s likely that the 706 front panel looks identical inside and this fix would apply to that radio series too.

The control panel after removing the vfo knob

Top right is the grey RJ series microphone connector, below that and behind the shield plate is the encoder. I unscrewed the nut on the encoder first. The PCB has to be lifted out of the case, a procedure I performed with a lot of care for fear of damaging the board or traces on it. Once the PCB is removed the encoder can be removed and the new one installed in its place. I removed the mike connector to get easier access to the encoder.

The PCB inside the control panel
The encoder with cable

After that I replaced the knob on the encoder shaft but it was loose and i couldn’t see how it was attached. Many knobs on Icom radios have a grub screw inside the knob, covered up by the rubberised section around the knob. Removing the rubber revealed nothing of the sort. Looking for help on the web I found reference to a small spring steel clip inside the knob. There was none inside mine. Then I found it on the workbench where it had fallen out when I originally removed the knob. A bit of careful work with tweezers put it back into the knob and the knob then went back onto the shaft and stayed there.

The spring holding the vfo knob to the shaft

Reassembled, the acid test was to turn it back on. Initially it appeared to be dead. I recalled a reset procedure and tried that without effect. Reading the manual page on the reset I found the correct procedure was to hold the up and down buttons then press power. Following that procedure the rig came alive, to my great relief, and I was able to tune in some broadcast stations using a 50cm piece of wire.

I now have to take the rig out for a field test to confirm it is back to normal.


Mt Rob Roy, VK1/AC-031 on 15th May 2020

I had been postponing a repeat visit to this summit ever since my only activation in 2013. The first 1km or so is very steep and is quite a challenge. However, with many of the VK1 summits inaccessible due to the Namadgi National Park closure, which followed the long running bush fire in the summer of 2019/20, I decided that this was my chance to revisit the summit.

Setting off from a laneway in the suburb of Banks at around 8:30 one frosty autumn morning I soon warmed up and had removed two layers by the end of the first kilometre.

The walk is about 5km, similar to the Bullen Range walk. It took me about 1 hr 40min this time.

Southern Tuggeranong suburbs of Canberra
After the first steep section
Starting out from Banks ACT
A turn to the left here
an intersection
Operator and trig point
On the air
This summit has one of the old wooden trig masts

After reaching the trig point, I set up the HF antenna and looked for contacts. There were plenty, mainly on 40m but some also worked on 80m and 20m. I did listen on 17m but signals were very low.

40m produced the most contacts, which were again mostly on CW, but with a few on SSB.

On 2m FM a few local contacts were made with Andrew VK1AD, Wade VK1MIC and another callsign who was new to me.

Weather: it was a fine day and was close to zero Celsius when I left the car. After the first 1km I had warmed up so much I removed my jacket and the fleece, leaving just a long sleeved cotton work shirt. That was enough until I had cooled off at the top of the climb, when I put the fleece back on. Sitting in the shade of a large tree I got cold after a while and was glad the sun moved enough to move the shade off to the east. By 11am it was about 10-12C, much more comfortable. No wind.

At 11 AM and after 22 contacts I was thinking of lunch so I packed up and returned to the car. Again it was well over an hour for the return leg of this summit activation.

On the way down I noticed I could see a number of SOTA summits to the north. Tuggeranong hill, Mt Taylor, Black Mt and Mts Ainslie and Majura in the far distance, about 25km away.

other SOTA summits visible from the Rob Roy access track

Overall I think this activation was a bit harder than I had expected despite having been here before, in 2013. After a 5km walk (each way) there is a certain amount of satisfaction in having made the summit and qualified it for the SOTA points.

Qualified the summit for SOTA using both CW and SSB. Contacts made on 80, 40 and 20m. Then also on 146.5 FM, local contacts using a 5w hand held radio and a half wave dipole antenna (flowerpot style). On HF my radio was an Elecraft KX3 and a ZS6BKW style 28m wire antenna, fed in the centre by a 11m length of 300 ohm tv ribbon. The feedline was connected to the KX3 via a home made 1:1 choke balun.

Mt Rob Roy is located to the east of the suburb of Banks in South Canberra. It is located inside the Rob Roy Nature Reserve which has a code in the WWFF award scheme. Access to it is open, though some of the walking path goes through grazing property so walkers are expected to close gates they open and keep to the path.

Amateur Radio

Bullen Range, vk1/ac-033, 9th May 2020

The walk up to the summit of Bullen Range is a 5km effort, with a few steep sections but mostly reasonably level walking along a fire trail. Access is from Tidbinbilla Road which connects the village of Tharwa with the Tidbinbilla Nature Reserve. Bullen Range is a few km west of the Tuggeranong Town Centre.

Bullen Range is west of the Tuggeranong Town Centre in southern Canberra. AC-033 is the highest point of the range.

The map above shows Tidbinbilla Road and the connection from the suburb of Gordon. The river shown is the Murrumbidgee. Crossing it at Point Hut Crossing and then turning right onto Tidbinbilla Road leads to a parking spot at a gate into the Bullen Range area just east of Paddy’s River.

There are six gates to pass and only one can be unlatched. You need to climb over the rest. The track goes to the west of Barnes Hill, then two right turns lead to an uphill climb to the ridge line. This 5km trip took me about 90 minutes this time.

After arriving onsite and making several quick contacts on 2m FM with locals, the HF antenna went up on the telescopic pole. A felled tree served as an operating table and a wood stump became a seat.

Just as the HF contacts started, the rain started. It had come from the west where my view was obscured by trees. The tarp I usually sit on was hastily set up as a rain shelter.

The radio and other gear was sheltered from the rain by a tarp. Photo extracted from video clip
in the original photo some raindrops were visible but they have vanished in the conversion from video

After the radio contacts dried up, and while the rain was still light, I packed away and set off back to the car.

Rain visible to the west on the return trip

After reaching the car and stowing the gear in the back, I sent a message to my WhatsApp group reporting that I was back in the car and en route home.


Travel distance to parking position. About 10 km from Tuggeranong town centre, south Canberra, via Point Hut Crossing over the Murrumbidgee river.

Walk distance from parking spot: about 5km each way.

Terrain and slope: along vehicle trails and fire trails. Some steep sections. Some rocky ground with slippery sections, care advisable. Six gates to climb over or go around (in one case only).

Summit elevation: 925m

Accessibility: good

Permission required: None. Location is the Bullen Range nature reserve, open to the public except in periods of total fire bans or when notified on the ACT Govt website.

Phone coverage: Optus and Telstra services are readily accessed here.

Amateur Radio

resuming this blog

I have found some solutions to the technical problems I was having a few years ago and I am going to see if this blog works ok with its revised technical setup.


Mt Coolum, VK4/SE-114, 1st December 2019

Visiting my daughter and family on the Sunshine Coast of Queensland, I had taken a basic set of SOTA activation gear with me in case an opportunity came up for an activation. While planning activities for Sunday 1st Dec I offered my grandson Jack (12) the option of climbing Mt Coolum with me and joining in a SOTA activation. He jumped at the chance and his mum was very happy to see him accompany me.

We drove up to Coolum having planned to start the activation at 2pm local time, 0400 UTC. Traffic was ok and Jack read out the navigation instructions from my Navmii app on the iphone as it was not delivering audio to the bluetooth connection.

There was a forecast for a storm to pass through the area and the radar showed a narrow band of rain and high wind. But when we parked at the foot of Mt Coolum there was no sign of bad weather north or east, though there was haze and cloud to the south.

So we decided to continue with the climb and checked the weather we could see as we went. The wind was very strong at times. At the top we found a fenced compound containing some comms gear. I wondered whether we would have much interference from the equipment there, but there was no alternative for mounting the light pole I had brought with me, a 6m thin fishing pole.

We set up the antenna, a trap dipole for 20/30/40m, fed with RG178. The insulator at the feed point has a small hole that the top of the pole can fit into.

The FT817 radio was hearing a lot of static from storms in the area, and some signals from other amateurs on the 40m band. I decided to start on SSB this time, to give Jack a chance to hear what was being said on air. The first contact was with Gerard VK2IO who was portable in a nature reserve in NSW. After that contact my CQ calls were not answered and I decided I needed to move to CW and carry out some contacts in morse code.

Jack had done a bit of morse code for a school project so he knew what it was but didn’t understand the morse I sent or received. I explained the CQ, TNX, 73 and RST codes to him. It was too fast for him though.

After 3 contacts on CW/morse I wanted a fourth so as to qualify for 4 activator points on the CW mode. And once again Bill VK1MCW came to my rescue. He wasn’t hearing me too well, but persisted and listened for my replies until he heard them. He then gave me a low signal report, as I expected, as his own signal was not particularly strong and I knew my transmitter was a lot less powerful than his, so he would be hearing a weaker signal from me. Finally we had confirmed our reports and completed our contact.

Then I noticed some spots on the ParksnPeaks site for portable stations operating on voice/SSB further up in the band. So we looked up there to see who we could hear, sure enough Alan VK2MG was received up on 7.144 and his signal was strong so we had a good chance of being heard by him. After a few calls from stronger stations, Alan heard our call and we were able to exchange signal reports with him successfully.

We looked again at the clouds to the south and the west. The wind was still strong but there was no sign of the wet weather getting nearer to us, so the sunshine continued. However we thought we had been on the hill long enough, it was difficult to make more contacts and we decided to pack up and walk down the hill.

On the way down we saw quite a few walkers coming up the hill. One of them was a very small child about 3 years old, holding mum’s hand. That is quite an achievement for a small child, and for mum!

Here are some photos of our trip.

The path up this hill is like a stone staircase

Wonderful views from halfway up

Jack sent a text to Mum from the top

Looking northwards up the coast towards Noosa

Amateur Radio field and portable SOTA

Booroomba Rocks VK1/AC-026 on 16/11/2019

I was invited to accompany Andrew Moseley VK1AD on this activation.  It had been some time since we activated together so it was an extra pleasure doing this one.

The previous time I activated this summit was actually also a joint activation with Andrew.

The main thing we both noticed both enroute to the parking area and on the walk up to the summit was how dry the bushland was, areas which were previously green and even slightly damp were bone dry this time.  The long drought had certainly made its mark even in southern VK1.  We both thought that the hot summer that has been forecast will probably discourage activations in the bushland to the west and south of Canberra, due to the risk of bushfires.  Walking an hour into dry bushland does not make much sense and in fact risks not only the walker’s health/safety/life, but also risks the life of rescuers.  Summer may be a quiet period in terms of local activations in the forests near Canberra.

The walk up to Booroomba Rocks features large rocks like these



The climb up to the highest of the three peaks comprising the Booroomba Rocks cluster requires descending into the bush between the two southern peaks, then climbing back up through bush and then onto the rocks, after which it is an easy walk up to the tree that my telescopic pole was lashed to, to support my wire antenna.  I operated on 40/20/17m and also called cq on 10m just in case something was happening there.  I made contacts with other mountain activators in New Zealand and in Japan, as well as several contacts with home stations within NSW, Victoria and South Australia. My total contact count was about 12.

Andrew VK1AD operated on 144, 1296 and 2403, using an FT817 driving transverters on the higher bands, each with a PCB antenna seen in these pictures.  He made at least 4 contacts on each of those bands.  A number of Canberra operators called him as well as several on other summits, including Ted VK1BL on Mt Ainslie and Bill VK1MCW on Mt Stromlo.  Wade VK1MIC called in from his home station as did Peter VK1JH and Matt VK1MT.  Dermy VK1DB also called on 144 to give his brand new callsign a workout.  He recently passed the advanced licence course.

I was pleased to find this climb was much easier than last time I came up here.  On that day we first activated Pheasant Hill and then came up to this one.  My feet were very sore after that day, possibly due to my walking boots being too tight.  On this occasion I wore the Merrell mid boots I had worn on my walk in Spain, which are still in good condition and still comfortable.  I did have a few aches the next morning, but that’s ok.

A good day spent playing radio and I got home in time to prepare for a social function in Canberra later that day.

Amateur Radio SOTA

Mt Gillamatong, 2nd Nov 2019

To get back into some sota activations I drove out to Braidwood and walked up Mt Gillamatong. I set up the gear and antenna near the trig point but was disappointed to find high noise levels and an almost unusable 20m band. And I had left my logging tablet at home as well as the 2m fm antenna – but that would have been unusable anyway as the FM HT did not work, see below.

I had a contact with ZL1BYZ on 20m band cw, no other callers there. Went to 40m and worked an S2S with Peter VK3PF/p (very low at that stage) and Steve VK7CW at better strength, called for a while on ssb on 7090, no replies. Noticed a JA had been spotted on Sotawatch calling cq on 18 mhz so went up there, scraped in a contact. Then worked another Japanese operator at a home location. Geoff ZL3GA then, still on CW on 18 mhz and by now it was after 0000 UTC so a second contact with ZL1BYZ was made.

All up, only 7 contacts, all on CW, despite some time spent calling CQ on SSB.

A message from Canberra chasers asked about 2m FM possibilities. I had the HT but its battery was flat and I had no spare. Sorry about that, guys.

After getting back to the car I visited the Braidwood Bakery and ordered a pepper steak pie and a coffee.

The KX3 in the sun, unfortunately

Not my dish

Base of the pole with guys

There’s an eagle up there to the right of the pole

On the way down the hill, looking east towards Braidwood


Activations in Spain continued

Thanks to the efforts of Guru EA2IF and Ignacio EA2BD I was able to activate more summits in Spain together with Juan EA1AER. Juan met me on the 21st of September, a Saturday in Léon, a very beautiful, historic city. Then he came back on 23rd Sept to take me for a trip out into some beautiful country north east of Leon.

The summits we went to were EA1/LE-197 and EA1/LE-165. These are north east of Leon requiring about two hours drive to reach the first.

The first required a good climb to reach the summit. From where the car was parked I actually doubted that it was possible to reach the activation zone. It looked steep and narrow. However I thought Juan had activated this in the past and assumed this was a well known summit. The climb started out as a mild stroll up a forest path then up some steps formed with wooden risers. I climbed up the lower sections quite easily, having just walked for almost 500 km in the previous 3 weeks.

Then it became a steep climb up earth and rock steps with a chain on the left for assistance. This was slower!

At the top the view was breathtaking. I could see the road but not the car as it was obscured by trees. It all looked a long way down. My photos probably don’t show it well enough.

The first few photos are mine. Then I have added some of Juan’s photos.

Some photos from Juan’s website are copied here too.

After erecting the end fed 20m wire it was tuned for best output power on the 817 and I called CQ on 20m Cw. Contacts flowed quickly. Then Juan made more contacts.

Finally we packed up and ate some lunch. Just as we were preparing to start the descent I received a message from Ignacio EA2BD asking if we were still on the air. I had to say no, as everything had been packed away. Disappointing as I would have liked to give him a new summit unique.

Juan remarked that I would be the first activator of the summit. I then realised that my earlier assumption was incorrect. It had not been activated before and it was the first time Juan had been there.

Juan then showed me some more of the sights in the valleys of this area.

We then went to another summit but the contacts made from this one didn’t qualify for SOTA.

This activation is also described on Juan’s blog at: which is written in Spanish (use Chrome browser for an approximate translation).

Here is a photo of most of the group of Leon hams who met us on the second summit, partly to meet me and partly to visit the club’s repeater site.

Amateur Radio SOTA

SOTA activations in Spain (3)

The next day after arriving in Pamplona and the activation with Guru EA2IF arrangements were made for another activation which would be NV-119 San Cristobal. This activation was made with Ignacio EA2BD. He had already activated this summit during this year.

The antenna, one I had borrowed from Andrew VK1AD, was a LNR EFHW and was setup as an end fed half wave for 20m.

With the antenna fed directly from the KX3 it was showing a SWR or 2.5 so I put the Elecraft T1 into the circuit, producing a 1.0 swr for the kx3.

This setup enabled me to make a number of contacts on both cw and SSB, on 20m. As it was the middle of the day we did not expect any dx and there was no signal from the USA or further afield.

Ignacio and I pose for the selfie

Yes I’m having fun…

I record here my sincere appreciation of the effort made by Ignacio to help me with this activation, also he drove twice to Roncesvalles, the second time was to retrieve the logging tablet which I accidentally left at the Bar there.

After the activation I was invited to join Ignacio and his wife and daughter for lunch at their apartment. This was a very pleasant occasion for me and I felt very honoured to be a guest in their home.

Thanks again, Ignacio EA2BD.


SOTA activations in Spain (2)

After reaching Pamplona and finding a hotel for some welcome relative luxury compared with the 8-16 double bunks in the bedrooms of hostels (typical of the low cost accommodation on the Camino) I had arranged to meet Guru EA2IF so we could activate a nearby summit,  Mt. Erreniega EA2/NV-092.

In fact he parked near my hotel and I easily found him when I left the front door. He was nearby and waving to me. So we set off towards the summit, chatting about SOTA, radios, antennas etc as radio hams do.

Arriving at the summit it was easy to set up the antenna and the FT817 with atu for 20m. Conditions were not as good as they had been three days earlier, but I made more than enough contacts to qualify the summit. As I had worked Ignacio EA2BD at this summit in 2018 this activation made this summit a “complete” (ie. worked and activated).

Guru was trying to make contacts using an economy HT on 439 MHz. There were no replies.

In an attempt to let him make at least one valid contact on 439 fm we walked down the hill far enough to be out of the activation zone. Guru returned to the top and called me using the ft817. I could hear the signal from the FT817 but the HT was transmitting so little power that the reverse path did not work. I walked back up the hill and was within 10m of the other radio before the HT was heard. Clearly a fault in the transmitter.

On the way down we passed the Alto Perdon with its monument to pilgrims and Guru told me I would pass that on my way out of Pamplona on Monday. You can find my pictures of the monument etc on my walking blog. Https:// Look for the post about departing from Pamplona, day 7.

We then visited the site of a contest station owned by local hams and I admired the rotary antennas etc. then we went to his home for a short time, then to a local club for a meal and of course a longer chat about the same subjects.

I first contacted Guru about the possibility of activations in this area. Thanks to Guru not only for the advice but the hospitality and for taking me up for those activations.

The feedpoint for the EFHW used on hf

Guru setting up the uhf antenna

Evidence of my presence on the hilltop

More evidence