The Bluff/Mt McDonald trip, New Years 2012/13

Hi all,

After getting back from a camping trip, which included a SOTA activation of Rocky Peak, I was off the next day on a planned VMTC trip to a range of high mountains to the south east of Mt Buller. The plan was to take in part of the Australian Alpine Walking Track which I had not done before. I only had two takers for the trip, so there were three of us in total. The VMTC requires four for an official club trip and we were one short, so this turned into a private trip. My plan was to activate for Summits on the Air a series of mountains that were taken in by the walk.

Getting started

The day started with a 7am pickup of a walker from the train station, and then we headed up to join another walker up in the Howqua Hills at 8 Mile Gap (506792). From here, we headed down Brocks Rd to the Jameson River. This is marked as a 4wd track, but it is maintained to a high standard, so no problems with a 2wd. We then drove up Low Saddle Rd. The standard of this road is not as high, but I was able to get the Prius to point 513754, which would take a bit off the walk on the last day. We then piled into a 4wd for a car shuffle and took the Refrigerator Gap Track up to Refrigerator Gap and the carpark for the walk up to the Bluff.

The Bluff VK3/VE-013

The Bluff is a shortish, but quite steep climb up from the Refrigerator Gap car park. Over 400m is gained from the car park over about 1km horizontal distance. Towards the top it becomes a little scrambly. I had to negotiate the squid pole a few times, but it was not too bad. The plan was to have lunch here, so my fellow bushwalkers would have their break while I operated radio. One little problem was that I did not bring anything to secure the squid pole, and there was no trees at the operating location. I used the base of a rock and my backpack to secure the squid pole, as shown:

Squid pole at The Bluff secured by a rock and a backpack

Squid pole at The Bluff

I used a Wouxun KG-UVD1P handheld radio for FM and a FT-817 for other modes. Using the Wouxun allows me to save the FT-817 batteries. Because the FT-817 is an all mode radio, its amplifier is linear, and not as efficient as the Class C amplifier in the Wouxun. I use a BNC adapter on the Wouxun, so I was able to change the antenna from one to the other radio with ease.

The activation was performed with my colinear. I decided not to do the match yet (as discussed in the linked article) as I wanted to make the stub with BNC connectors which I am waiting for an order of these to arrive. The unmatched colinear has a poor, but not unusable match. The FT-817 would reduce power a little, but this level of mismatch (between 2 to 3) would not damage the finals. I estimate it would be 4dB or so down on a fully matched performance. Still worthwhile to give it a go and also to compare its performance to when I do have it fully matched.

It certainly does perform. I know some think that I would be better off with a Yagi, but for this kind of walking, this colinear does hit the spot. I tried it against a few repeaters and would give it at least 15dB ahead of a quarter wave whip antenna. One repeater was very scratchy on the quarter wave, I could barely break the squelch, but with the colinear, it was nearly (not quite) full quieting. Being omni-directional on the horizontal plane is also a bonus.

In the end, I was able to work into Melbourne, and looking back at the results, I was about 5dB down on what I would have expected from an optimised colinear. I think I’ll gain most of that with the match. I was also working a few stations well away from Melbourne.

Here are some pics from The Bluff:

Looking west from The Bluff

Looking west from The Bluff

Looking east from The Bluff

Looking east from The Bluff

Mt Lovick VK3/VE-020

After lunch, it was time to head off The Bluff and head for Mt Eadley, Bluff Hut and then Mt Lovick. There are two tracks marked passing Mt Eadley Stony, but we only found the higher track. The Bluff Hut has been rebuilt after the 2006 fires, but is not used as part of the cattle muster as cattle are now banned from the Alpine National Park. It was fairly late in the day when we made Mt Lovick and we camped almost right on the summit, far enough away for some dirt to put tent pegs in.

Camping at Mt Lovick

Camping at Mt Lovick

I tried 2m again from here. I was able to complete 2 QSOs using FM, and then 1 contact with VK3AFW using CW. I then went to 40m to get the last contact required for activation – plus a pile more.

Here are a few late evening pics from the summit:

Looking east towards the King Billies from Mt Lovick

The King Billies from Mt LOvick

Looking south west towards The Nobs and Mt McDonald from Mt Lovick

The Nobs and Mt McDonald from Mt Lovick

Mt Clear VK3/VE-018

Up the next morning, Sunday the 30th. We left about 9 and headed for the King Billies. Our first water stop was from the headwaters of the Jamison River, just underneath Picture Point at 634832. I treated the water with the SteriPen Adventurer (a UV treatment), another walker, Adrian used tablets, while the third, Clive, drank it untreated. I still reckon that the chances of getting sick are low, but because I have been sick from drinking high country water, I don’t take that chance.

We arrived at King Billy No 1 and had lunch there. I wanted to save my operating capacity (i.e. batteries) for summits that I could get SOTA points for, so this went begging. I activated this earlier in the year, late at night and in the fog. I was able to see my old operating location, just underneath the summit. Here’s a look at Mt Magdela (Marjorie VK3/VE-012) and the Cross Cut Saw to the left from King Billy No 1 VK3/VE-016.

Looking east at Mt Magdela from King Billy No 1

Mt Magdela from King Billy No 1

With lunch done, we followed the quite indistinct path to King Billy No 2, and then lost the path and made our way to the road junction at 650812. From here, there is a management vehicle track (with trees fallen over it) heading down towards Mt Clear. We drew water at 642787 and made our way to the base of Mt Clear. The management track leaves to the west, and the start of the walking only track is a little unclear. This is at 627766. From here, the track climbs quite steeply, but not quite as steep as the track up The Bluff. Still a good effort for late in the day. We arrived at the summit and camped within a few metres of the summit.

I attempted activating VK3/VE-018 on 2m, but had no success either on FM or SSB. It was then over to 40m using the end-fed, where there was no difficulty. With the end-fed, 40m is the old reliable.

Here’s a pic of Mt Buller, Mt Sterling, Mt Lovick (closer) and Mt Cobbler from Mt Clear. All of these mountains are SOTA summits.

Looking north west from Mt Clear

Looking north west from Mt Clear

The Nobs VK3/VE-040

The next day, it was up for an 8:30 walking start. First task of the day was to get a water top up. I only had a small amount left, and some of the party was dry. We obtained this at 617729, where the creek was about to descend rapidly down the side of the mountain. From there, it was following the indistinct path down from Square Top and towards High Cone. High Cone appears to have exactly 150m prominence, so it will become a SOTA summit someday, but it is not one at the moment. There is a bypass track around High Cone, so we took this. It’s more of a route as the track is quite indistinct. It follows just above a set of small cliffs. One gotcha with this mountain is where the spur comes down, the track continues to contour around. We headed down the spur at that point for about 15 minutes before we realised our mistake. We then worked our way around to the right spur, but this took more energy and time. It was a late lunch when we arrived at the Nobs.

Given the lateness, I decided that I would only do 40m on the summit. I activated the summit quickly, but disturbed a large number of insects nesting in a tree where I was setting up the squid pole.

Mt McDonald VK3/VE-026

From The Nobs, it was a quick drop down along the still at hard to follow at times track towards a 4wd track. We headed along this to where the walking track leaves it to head up Mt McDonald. We needed water for the night camp, and so we headed down the 4wd track to get water. We got it from the second creek at 543729, but we had to go in about 10m from the road and burrow into what was almost a little cave to get it. This took quite a lot of time, and meant we would get to the top of Mt McDonald very late in the day. It was a lot of effort getting up, and the effects of the long day were definitely having an impact. We lost the track at one point and tried to sidle around the side, but this was very hard work, and felt dangerous. I then climbed up a very steep section to regain the track that was on the tops. If climbing Mt McDonald from the east, try to stay on top of the ridge if you don’t know where the track is.

We arrived with about one hour of light left at the summit. I was pretty exhausted, but I still wanted the SOTA points for all this effort. I setup the tent and then the amateur radio station:

Camp site and operating location at Mt McDonald

Camp site and operating location at Mt McDonald

The views from all the summits that I had visited so far on this trip had been spectacular, but a great deal of the southern high country can be seen from Mt McDonald, including Mt Donna Buang, Mt Torbreck, Mt Baw Baw, Mt Abrupt, Mt Alexander (near Bendigo), Mt Hickey, Mt Buller, Mt Howitt, Mt Cobber, plus most stuff around Licola. Here’s a view looking back towards The Nobs and Mt Clear:

Mt Clear, Square Top, High Cone and The Nobs from Mt McDonald

Mt Clear, Square Top, High Cone and The Nobs from Mt McDonald

It was a great way to see out 2012 with the views we had from up there.

Mt Sunday VK3/VE-050

The final summit for the trip was Mt Sunday. The SOTA program works on UTC time, and a summit can be activated for points basically once a year. There was an opportunity to activate this summit twice, before UTC midnight (11am local) and then after. It was break camp at 6:50am to give myself a chance to do this. The other guys were completely disinterested in the radio part, but appreciated walking in the cooler time of the day. It was about an hour in that I realised that I might not make it to Mt Sunday in time, so I had to burn rubber. I walked very quickly down the track – which was easier to follow on this side of the mountain. I made Low Saddle at 506678 and left my pack there. The top of my pack converts into a little day pack, so there was enough room for the FT-817, the end-fed cable, a coax cable, the microphone, a notepad and a bottle of water, a LiIon battery and that’s it. It was time to head up Mt Sunday. The track is a little indistinct to get started, but then was easy to follow. It has also had the fire regrowth slashed back. This might have been quite difficult to follow two years ago, but is changed now.

I arrived, after a hard climb, at 10:45am. I operated north-east from the summit, about 15 to 20 vertical metres down. The summit has lots of trees, recovered from the fire at the very top, but burnt to a crisp elsewhere. I hung up the end-fed in the regrowth saplings and began to operate 5 minutes before UTC midnight. I was able to get 7 contacts in that 5 minutes, three of them in 1 minute. I felt like a contest station there for a bit. I continued to operate after 11am local, but it was far more relaxed. It was also nice to work VK3AFW and VK3PF who where both activating summits on both sides of UTC midnight. 4 lots of s2s! At 11:30 it was time to pack up and start the long trip to the car. I arrived back at my pack at 12:20pm which had a note from the others that they left to head for the car at 11am. I was an hour and 20 minutes behind.

It took another 4 hours and 20 minutes to walk the 11.5km to the car. I had a lunch break, but I was very low on water. I found water in several creeks. The first was a little desperate and I am very glad I could UV treat it. The others tasted better. The effects of the previous day had again caught up with me, plus the big effort to get to Mt Sunday in time. I was pretty tired when I got to the car at 4:40pm. I started 1:20 behind, but lost another hour to them. They could not keep up with me earlier, but now I could not even nearly keep pace with them!

After that, it was a shuffle back to the other car at Refrigerator Gap underneath The Bluff. I realised I had left my CW keyer at Mt Lovick, a day’s walk behind, but Adrian agreed to drive up there as it is close to the 4wd track. That track certainly is for 4wd only. He was eyeing off the place for future family camping visits, but I am thankful that I was able to retrieve the keyer.

It was time then to head for Mansfield and a much needed feed. Never has a bottle of soft-drink tasted so good.

Regards,
Wayne VK3WAM

Constructing a 2m colinear Part 2

Hi all,

This is a continuation of Constructing a 2m colinear Part 1.

Repairing the Colinear

On a recent SOTA activation trip, I tested the colinear in the field. As discussed in that post, the lower SWR point seemed a little high. At the second and third activations on that trip, I was unable to use the colinear due to a persistent short. This short turned out to be in the BNC connector.

After coming back from the trip, I set about repairing the antenna and upgrading the connections to make them more robust. This was done using some spare foam dialectic from some RG6 cable I had lying around. I had previously used the braid from this for another project. This dialectic could now make itself useful as a physical shunt to give the joins of coax some structural integrity. I simply inserted the dialectic into the join area and secured it with tape. Seems to work well, and the colinear does not feel anywhere near as fragile.

Analysing the Colinear

Once getting the colinear fixed, I put it up at home in the backyard to have a look at its frequency characteristics. I used a MiniVNA Pro with the BlueVNA app running on a Samsung Galaxy S2, using bluetooth connectivity. Here is a screenshot:

Colinear screenshot from BlueVNA showing SWR, impedance, resistance and reactance

Colinear screenshot from BlueVNA

Several things to note from this picture is the SWR is unacceptably high. The FT-817 reports a lower SWR as some is being burnt up by warming the coax. Also, the resonant point is at 147MHz, when I was expecting 145. Before we get too excited, one thing to remember is this is a picture of what is at the BNC connector, not what is actually at the “feedpoint” which is through the common mode choke, up to the first coax connection, about 910mm of coax away.

Here is the same data using Zplots, which is an excel spreadsheet. The data from BlueVNA was saved to a s parameter file, which can be loaded into Zplots.

A Zplots render of the Colinear at the BNC connector, showing a graph and a smith chart.

Colinear at the BNC connector in Zplots

This zplots chart shows much the same information as the screenshot from BlueVNA, which is no surprise given it is based on the same data.

Zplots has the capability of compensating for the effects of transmission lines. I could then algorithmically have a look at what is going on at the actual feedpoint, which would be very difficult to physically access. Here is a screenshot from Zplots at the “feedpoint”.

A Zplot, consisting of a graph and Smith chart with compensation for the transmission line.

Colinear characteristics at feedpoint

This graph shows the antenna is resonant at 144.7MHz, which is not far from what the antenna was designed for: 145MHz. The gotcha is that the resistance at the point of resonance is about 14 ohms. No wonder there is bad SWR on this thing. This is a prime example of how a resonant antenna does not necessarily have low SWR.

Remediation

What to do about about this antenna that is resonant where planned, but effectively gives me an SWR of 3 to 4 over the entire 2m band? I am going to have to do some impedance transformation to match to this antenna. What to do?

There is another Smith chart shown below. The purple dots represent the impedance at various points from about 144MHz up to about 146.5MHz. These points are effectively the same as the “feedpoint” data calculated by Zplots, with 910mm of 52ohm coax (RG58/U) being added to the data obtained at the BNC connector. Along the coax from the connector to the feedpoint, they essentially rotate on the Smith chart around the centre point. The centre point is, by the way, a 50ohm 1:1 SWR point. This is where we want to be, or at least within the red circle on the Smith chart.

I have more choices than right at the BNC connector or at the “feedpoint”. The first 500mm from the feepoint is a bit hard, as it is inside the aluminium sleeve of the colinear. This bit of coax is inaccessible. About a 290mm segment is also not accessible because it is in the common mode choke. There is a section about 350mm (360mm from where MiniVNA would have measured from) from the BNC connector that looks nice. This is 545mm from the “feedpoint”. This is represented by the smaller green dots. From here, I can use a parallel shunt bit of coax. If this bit of shorted shunt coax is 160mm long, then the impedance is transformed into the “matched” zone.

Impedance matching the colinear antenna using a Smith chart tool. The Smith chart shows a transmission line and then a shorted coax parallel shunt

Transformation of feedpoint impedance

One draw back is the cable will have a DC short because of the parallel shorted coax shunt, but this is a “nice” short.

73 de Wayne VK3WAM

3 summit activation: Mt Mitchell, Sugerloaf Peak & Federation Range

Hi all,

After my building of a colinear antenna for 2m, it was time to try it out, and what better than a SOTA activation. I picked three summits that were close to each other, and where it was possible to get into Melbourne on 2m, but only one of these summits, Federation Range VK3/VN-003 had anything that was close to line of sight.

Mt Mitchell VK3/VN-012

After getting my gear together early on Friday morning, I headed out (about an hour late) up to Mt Mitchell. There is a well made gravel road that leads up to close to the summit. The main 2WD road skirts the edge of the activation zone, getting about 5m into it. So, it is best to park the car a little down from a junction NE of the summit with a 4WD track. This track is mostly in the activation zone and passes over the summit to the north and then the west. Being 2m, I wanted to be at the summit itself to get good takeoffs in most directions, especially south and west. Approaching from the north west meant summitting.

The vegetation is recovering from the 2009 bushfires. The fire here was intense and killed nearly all the trees. Regrowth is currently about 2m high and is not too bad to get through. There are also rock areas about 10m across to make things a little easier. I found one of these close to the highest point and set up here to operate.

I was wondering how the colinear would go with electrical shorts, and it was no surprise to find that a short had developed when I set it up. Thus began a process of taking down the squid pole and checking the various connections. One thing that I have noticed is that because I used RG58/U – to obtain a shorter antenna – with a stranded centre conductor, the setup is far more susceptible to shorts. When I did the soldering, I did not have the best light. I am going to have to resolder the connections and ensure all strands of the centre conductor are captured by the solder. As it is, there are free strands that make their way where they are not supposed to.

After about 20 minutes of stuffing around, I managed to get a short free colinear. I was running way behind time, so I did not bother getting a VNA readout of the colinear. It has acceptable SWR over the whole 2m band, but it could be optimised as it looks like the centre point is at the top end of the band. This means the positioning of the choke on the input cable could be pushed out a little.

The colinear worked well. I was able to make a contact with Peter VK3PF down in Gippsland, even though there are quite a lot of hills causing obstruction over the path of well over 100km. Clearly this thing has some gain. The only comparison that I made was into VK3REC, an EMDRC repeater. The 1/4 wave on the HT could break the repeater. The RX was scratchy, so you had to move around a little. The Colinear had it well over 5 and 9 plus (I guess 20dB). So I need to fix up the shorting problem to get this baby on the air more often.

I was present at the activation area for about an hour, but with the stuffing around to locate the short in the colinear, I only operated for a little less than half an hour. I headed back to the car, grabbed some quick lunch at Buxton and headed for Sugerloaf saddle underneath Sugerloaf peak in the Cathedral Ranges State Park.

Sugerloaf Peak VK3/VN-011

I have been to this summit twice before. The first was many years ago, when I was not very experienced in overnight walking. We (my wife and I plus some friends but I cannot remember now who they were) camped at Farmyard, about 3 km to the north. We planned to head down to Sugerloaf Peak and return to Farmyard. It was overcast and foggy. We never made it to Sugerloaf due to a few spots on the “track” that were very exposed on the rock.

My second attempt was as part of a warm up for a 16 day walk in SW Tasmania. I was walking with a guy to train him up physically for the Tasmanian walk. He is an experienced rock climber. There is a path that goes up the side of Sugerloaf Peak that he said would be graded 3. He said it is much harder when carrying a full pack. Nonetheless we went up. I would have never have gone up without him, but he clearly knew what to do. Foot here, press against that, move other foot there, etc. I just did what I was told and he made it look easy. I, of course, had no idea of what to do. The tables were turned a few weeks later in SW Tasmania, where luckly I knew what to do out of the group that went down.

So for this my third visit, I headed up the “less hard” track, which still has lots of open, exposed rock. It would be tricky when wet, but in dry conditions, just take good footwear, and don’t look down too much.

Also, since the fires, there has been an upgrade of facilities at Sugerloaf saddle. There is a nice shelter there now which could fit more people than would ever likely be there at one time, ever.

I made the summit in good time. Check the colinear cable – no electrical shorts. Looking good. Raise colinear – shorts! Try as I might for the next 45 minutes, I could not find the short. Do I raise the end fed on 40m, or get out the 1/4 wave. This is supposed to be the hardest summit of the day, will the 1/4 wave on 2m even make it into Melbourne? Turns out it did without too much trouble. I did not get any contacts on FM, but SSB saved the day.

I should make mention of the BHI NEDSP1061-KBD noise reduction module here. I have one of these installed in my FT-817, and in my FT-897 as well. It does make SSB easier to listen to, but it can also improve readability where the signal is on the limit. It helped two of my QSOs today, pulling what would have been R3 to R4, and R4 to arm chair copy. If something is R1, it won’t help it, but if it is R2, it can pull it to R3 and you’ll get the QSO that you would otherwise would have not.

Sugerloaf peak is the most scenic of the summits of the day, so here are some pics.

Looking north west from Sugerloaf Peak

Looking north west from Sugerloaf Peak

Sugerloaf Peak, looking north, with sheer drop off to the right

Sugerloaf Peak, looking north.

Notice the drop off to the right on the pic above (click it for a better view).

Squid pole with colinear on Sugerloaf Peak

Squid pole with colinear on Sugerloaf Peak

Federation Range VK3/VN-003

Time for the final summit of the day, Federation Range to the north of Lake Mountain. I headed up to the ski resort and parked in the main car park. This place is D E A D during summer. I headed up the XC ski trails heading north and after about 30 minutes made it to the top. The activation zone is fairly large, but again, 2m makes you want to operate from the highest ground. This time I did not bother to attempt to operate the colinear. I simply plugged the 1/4 wave into a Wouxun KG-UVD1P and started up. I made two contacts on FM, but then things were slowing down. Time to plug in the FT-817 and I got 5 more contacts on SSB. Even Peter VK3PF got a look in. The path to his QTH is not clear, but there is much less in the way than at Sugerloaf Peak. I still think that if the colinear was able to be operated there, he would have got that summit in his log.

The activation here was short as I wanted to try and be out of the resort area by 6:30pm. In the end it was closer to 6:40 when I was back on the Marysville Woods Point rd, but it seemed not to matter. It was an interesting day for 3 summits and 20 SOTA points, all on 2m. It would have not been possible without SSB, but I need to get this colinear working! Even though its first adventure did not quite work out, I think this antenna has already shown its promise and with a little corrective surgery, need not be a pain in the rear end!

One little side note: I took up some 18650 cells, but in the end the internal battery on the FT-817 was able to last through all three activations. It was getting a little tired in the end, and if I had wanted to keep going, I would have needed to plug in the external power. It lasted about 1 hour 30 minutes of operating, but that included quite a bit of FM at 5 watts, which is going to hit it harder than CW or SSB at full FT-817 power.

Regards,
Wayne VK3WAM

EDIT: There were a few shorting possibilities in the colinear. I used some unused RG6 insulation to provide a shunt on the joins to provide greater structural integrity. The BNC connector itself had developed a short! I have a good crimping tool, but these are the hazards with working with stranded centre conductor coax.

Constructing a 2m colinear Part 1

Hi all,

My recent 6 summit SOTA trip contained a few QSOs on 2m. All bar one of mine were using a Wouxun 2/70 HT with a 1/4 wave antenna on 2m. This is convenient, but is really only one step up from the stock antenna supplied with the unit. The antenna uses the radio and the operator’s arm as a (in)effective counterpoise, imposing significant loss to the system, well over 10dB. It’s time for a bit of gain.

Why a colinear?

I had a look at N1HFX’s colinear page among others. There are various types of colinear out there, some are based on a jpole, while this is a series of alternating half wave sections. The design from N1HFX is about a permanent installation, but I wanted something that could be used on a SOTA activation. There is a debate about whether to use a beam or a high gain vertical. The beam can be changed from horizontal to vertical and back by changing the mounting of the beam, but here in Victoria, most chasers would have vertical orientation. Horizontal does come out on field day contests, but aside from that vertical does seem the go.

A second consideration is that chasers might come from a variety of different directions. A beam is going to have a main lobe in one direction, with a series of nulls in others. This is good for some use, especially where either the direction of the wanted station is known, or there is some local source that is wanted to be nulled out. On most SOTA summits, there is not large local sources – obviously there are exceptions – but also radios such as the FT-817 do have good rejection of these. The chaser direction is not always known, and can vary quite widely.

For these reasons, I decided to go for a colinear. I also plan to use it as my vertical antenna alongside a Quadruple Quad for horizontal on the John Moyle MFD, which is the only VHF/UHF contest that I spent much time thinking about. Even for that contest, I generally think about running a station, taking advantage of my equipment optimisation for SOTA by going to places that require foot or non-car access to the summit.

Squid Pole and Coax choice

In the last few months, I have been often using a 7m (actually 6.8m) squid pole to provide a centre mount for a 20/40m end fed or the structure for a tunable vertical antenna for the HF bands. I began to think that this squid pole could provide a structural platform for a 2m colinear. The N1HFX design calls for 8 half-wave segments. I have been using LMR195 for a lot of my coax cables. This is a RG-58 replacement with better loss performance. One effect of this is that it has a higher cable velocity, measured with my MiniVNA Pro at around .825 One issue with these higher velocity ratios is the cable needs to be physically longer, compared to RG58. So, I needed to actually use RG58, rather than a drop in replacement for this colinear. I bought some from www.rfsupplier.com/

The MiniVNA Pro measured the RG58 cable from rfsupplier at 0.66, so this makes for a shorter setup than LMR195. It will actually fit on the Squid Pole with 8 half wave segments, rather than having to go to a 4 segment version. This should make for a nice antenna.

The first job is to cut up 8 lengths of RG58. I settled on a centre frequency of 145MHz. This is to provide for 144.1 SSB and for 145.5 and 146.5FM simplex not being too far away. We’ll see how that goes. Each length needed to be 300/145 /2 *.66 = 682mm. Add an extra 8mm for the overlap needed between two segments as per N1HFX’s design. Here’s a pic of the 8 segments cut and both ends stripped:

8 RG58/U segments cut and stripped

Then, I needed to join up the 8 segments as per the N1HFX design. Here is a look at one of the joins. A reminder that any image on this blog can be clicked for a better view:

Coax join to swap centre conduct and braid

It was a little tricky ensuring that there were no shorts between the two centre connectors. A stray bit of braid could some down (and sometimes did) to effect a short. I needed to continually check for this while soldering each connection. This is a gotcha with this design. I did pump on a good amount of solder to provide a good join and taped up with electrical tape to ensure the braid stayed away, and also to prevent water getting in.

The top end of the colinear needs a 1/4 wave segment, but only connected to the centre conductor. I grabbed some old RG6 cable that I had already stripped away the braid from for this purpose. The bottom end needs a 1/4 wave sleeve connected to the input coax braid. I used some aluminium tubing for this. Finally, there are dreaded common mode currents with a colinear. N1HFX has a choke at 1/2 wave down the tube for this. Obviously they cannot be put at the feed point because of the 1/4 wave sleeve, so 1/2 wave down the feed-line has to do. I would much rather a few turns. I could have gone for more turns on some PVC tubing, creating what is essentially an Ugly Balun. I went for three small toroids with 3 turns. This should provide a very high impedance to a common current, and at 1/2 wave from the feedpoint, this high impedance will be presented to the antenna.

Here is a pic of the completed coaxial colinear:

Coaxial colinear for 2m

Now, all I need to do is to carry this and the squid pole on site, mount the squid pole and the end of the colinear on it, and I have a BNC connector to go in the FT-817 or any similar style radio. I’ll test on a SOTA activation in a few weeks.

Regards,
Wayne Merry VK3WAM