Theremin and CW

Yesterday, I decided enough was enough, and that the power supply for Daz's theremin just had to be completed. So, with a mug of tea, and the fan heater running flat out, i ventured into the garage and cracked on. A bit of customising was required on the case, but the power supply is now finished. +/- 12v dual rail, independently fused, to a standard 5pin 180deg DIN plug. I can now, when i have the time, start working on the main Theremin circuit again.

I also built an incredibly simple circuit - a meter tester. This is nothing more than a 1M linear pot and a AA battery, housed in an old shaving stick. Yet, oddly, it doesnt seem to work properly! Everything seems to measure ok, but when on a meter, its all or nothing. Odd.

Since ive decided to make the concerted effort to master morse, I though as well that getting the practice oscillator running properly was in order. Up until now, the headphone output had a strange 'drop-off' tail on key up. The output transistor, a BFY51, was feeding the speaker via a 100uF electrolytic and a 100 ohm emitter load as a common emitter circuit. I suspect the cap was responsible for the problem with phones at low levels. I tested it today with the load resistor replaced by an audio transformer, and the speaker and phone socket on the secondary, and it seems to work just fine. Only problem, it no longer fits the box its in. So rebuilding it will have to await the Wakefield rally in a couple of weeks to aquire a suitable box.

The next little project is just that, little! I have a stash of ZN414 equivalents, and Sam has shown an interest in a matchbox receiver. Its a long time since i built a little AM receiver, so i think we'll have a go at this. Just need the matchbox!

Bent-Runner

Well, the weather has been dire today, far too cold and damp to put either mast up, or to run the coax. So, it has been indoor tasks only.

The VHF vertical doesnt fit on the top of the Clansman mast. I need a spare mast section to cut down to form an adaptor to allow mounting of antennas like this, but short of buying a whole spare mast, it might be hard to come by. Ive put the feelers out.

As for the telescopic mast, the big task was meant to be fathoming out suitable guying. I think a stay point at the 4m and 7m levels is needed, the bottom can still be held by the 1m level bungees, and the antenna wires will attach at the 8m level. Except for verticals, the top two sections are too thin to be of use. Ive a couple of sheets of PVC gluing together to make a thick rigid sheet from which to fabricate guying rings. As the mast tapers, each ring will be unique to its level, and so they will only fit in a set order. The other problem is tensioning the guys. The Dacron line i have, whilst incredibly strong, is very thin, some 2mm if that. £3 in Yeomans, i found a pack of ten 'bent-runners', ie guy line tensioners for tents. These have got big holes in them so i didnt think they would work, but the homemade one i fabricated earlier today the holes were too small, and passing the line through would be awkward. A quick trial with one of these and a length of the Dacron however and the seem to hold fast. I might have cracked that problem!

I have played some radio today, tried for HK0NA but the level of idiocy and QRM was astounding! Did work a SOS radio week station in Torquay though.

Antenna Work & VP8s

Up the side of the house today, removing the remains of the wind shattered 2m slim jim, and salvaging its coax. Luckily, the rain hasnt got into the coax, so that can be rerouted up the rear of the house and into the loft, where i can then use it as a test bed for smaller, short term antennas, with a dipole orientation N-S (so a chance to work the African continent on the higher HF bands!)

Anyone who knows me will know i have no fear of hights, but i hate ladders!

Ive already made an 80m inverted V for use with the 10m mast, plus a 10m J-pole. However, with the new year started and the offer of the SES for the Doncaster Show in september, somewhat more radical, practical and portable antennas are now needed! Apart from 2m FM (the mainstay of town SES'es) such a 2 day event calls for HF, and a selection of bands to cover eventuallities. Ideally of course, i'd be able to use any band, but that would call for a compromise of the G5RV type, and two masts, at least. This may be possible using mine AND G7PZLs 5.4m clansman masts, but it wouldnt be very high. So, a fan dipole/maypole design based on the 10m telescopic mast is needed. The question is - which bands?

In the past, ive found 80m to be a prerequestite for SES. So which others? 40 and 20? What about 15, 12, and 10m? Topband is out on the practicallity side, and 30m isnt needed as this will be a phone op.

Im going to test a few ideas out tomorrow based on the clansman 5.4m mast, at the very least to verify that it will take the 2m vertical without any issues!


On the operating side recently, not much! However, yesterday i was very pleased with my little tune around on 17m whilst taking a break from gardening. Heard VP8LP Bob, calling CQ, no replies, so thinks i, grab him if i can before the EU zoo arrives! So, i called him, little realising i was set to 10w. Anyway, to my immense amazement, he replies! I quickly hit the button to go to 100w, as 10 just wasnt going to be reliable, and instead hit the AM/FM button. A good few seconds later i was back in control, and Bobs phone is ringing! I QRX, he returns and we have a pleasent natter for a few minutes. I give my 73 as i need to crack on with the veg plots, but Bob asks if i'd like to work another VP8 before i go? (Having been after the Falklands ever since i got HF, then its a moot question!), turns out Zorro VP8DNT is visiting Bob, they quickly change over, and ive got two VP8s logged in 10mins!

80m Field Vertical

Im going to get cracking with this. I have a 10m fibreglass telescopic pole (a windjammer), for which i have already worked out a neat guying system using bungy cords, and have created a radial plate for it.

The proposed design is a top-center loaded vertical. The coil will be positioned 8 ft from the top, allowing that bit extra wire for capacity. Calculations show this should be about 55% efficient. Combined with my MKARS-80 giving 3-5w, this should let me have an erp of about 2w. Not great, but the real benefit is expedience - i can get this rigged at a portable site/summit in about 5mins

Im also considering a linear loaded coil vertical. But winding the coil every time i put the pole up would be slow, tedious and inaccurate. I wonder what a slinky streched over 30ft will resonate at???

QRV 6m

Well, ive not updated this for, ooh, i dunno, ages. Other things have taken the time.

Anyway. I now have the doublet back up, and its working ok. Its not perfect, but its working sufficient to make contacts, including some nicely impressive DX. Yesterday, on 17m, i worked Cuba with just 10w, for example.

The 3 element yagi for 6m is up, albeit on the 'test' mast, at about 15ft. 6m is very good at the moment, plenty of sporadic E to work.

The one thing that has struck me about working SSB on 6m, is the business-like operating. No messing about, reports and locators, and then clear, but at the same time not overly rushed. Very pleasurable short QSO's.

Im still considering the best way of securing the main mast to the side of the house, im not at all happy with expansion bolts into engineering brick, i just dont think they will hold well enough if they penetrate one of the voids. Im wondering about using a steel backplate and M10 threaded rod right through the wall for the top bracket, which will take the worst of the wind loading. The pole i have is steel, so its heavy. Maybe i should bite the bullet and get an aluminium pole ordered!

Julie is not particularly keen on the 6m yagi, so would be even less happy with the 9 element 2m Tonna. But if they were up at 30ft, perspective means they look smaller. They will also perform better!

Getting it up

The sealant cured on the slim jim, and its now mounted in its tube at about 15-20ft. Oddly, the SWR has gone up, and its now between 1.3 and 1.5:1 across the band, the lower figure towards the high end. Ive not had chance yet to do an on-air check, but receiving using the FT-290 plenty of repeaters and a fair bit of simplex is about. Interference from the ADSL modem was still bad, but some serious coil winding has removed most of it. I found the majority was coming from the network connection.

The HF doublet is shocking. Im blaming the change to a 1:1 coaxial choke balun, from the 4:1 collins. But the state of the feeder is also a worry, its been patched up several times and im sure there is still corroded sections. I have a 100ft roll of shiney new 450 ohm ladder line awaitin gthe rebuild. Probably i will go for a 135ft version, fed right back to the shack with 450 ohm. Im going to invest in a bottle of liquid tape for weather sealing the connections, and will also wind and solder the connections from the feeder to the antenna elements. Any splices in the feeder will be done to ensure continuity of impedence, and the feeder will be stood off from the fence etc along its path using electric fence insulators. I can then experiment back at the shack entry point with baluns etc.

I also took delivery of a 100m drum of 1.5mm2 conduit wire today, bought especially for antenna building, in particular for trying a 'stealth' 17m vertical mounted in the tree, with four tuned radials.

VHF Omni

fed up of having no antenna for 2m, other than an indoor whip, and with the prospect of getting the beam up still a way off, i set about coming up with a cheap and dirty 2m omni. My plan was to build a coaxial collinear, but having taken stock of what materials i had laying about, decided that for simplicity i would build a ladder line slim jim.

Initially, i designed my own, taking account of the velocity factor of the line. This worked, but i couldnt get the SWR down below 1.5:1. The matching section was made from 1mm mains wire stripped, as 300 ohm ladder line is a begger to strip neatly.

However, a review of the designs had me adding a few centimeters more line, in accordance with other designs on the 'net. This new version comes down to 1.2:1 at 145.500MHz, rising only a little at the band edges. All this is at ground level and indoors. An outside test at 15ft with the original showed the SWR to come down.

Now, its pretty much useless as is, built on a length of wood. So a trip to the wholesalers brought in some 20mm PVC white conduit. The whole assembly fits neatly into a 2m length, with plenty of spare tube near the bottom for mounting the antenna. I did a 1min microwave absorption test on a sample of the tube, and it was barely warm, no more than would be expected from being near a cup of hot water. A few holes drilled allowed cable ties to secure the antenna inside the tube, and some sealent in either end waterproofs it. The seal is domed carefully by smoothing with wet fingers at the top, whereas the bottom seal around the coax was done by shoving the mastic nozzle right in and giving it a damn good squirt. Some self amalgamating tape finishes it off by sealing the cable tie holes. Its attached to my test 100ft RG-58 cable at present, eventually this will be severed at about 5ft and a BNC added.

All that remains, once the sealant has cured is to mount the antenna and test it on air.

Getting my wood up

I now have everything i need to put the two VHF beams up (other than a rotator), pole, brackets, coax, connectors, and tape. BUt the weather won't let me! when the weather is fine, theres no one about to assist, and this isnt really a job i can do on my own.

I built today a wooden mast from 2x3 tanilized timber and galvanized bolts. This is just over 30ft tall, and will carry one end of my doublet via a pully block. It is semi-free standing. It will be fixed to a laylandii tree trunk, and have the bottom sunk into a brick lined hole. There will be a few guy ropes, but the purpose of these is to act as fall arrestors should it fall for any reason, and to swing the beast safely into the hedge. Only one guy will be for another purpose - to take the force from the antenna. I cant put this up yet, because i dont have suitable fixings to attach it to the tree yet, and besides its dark now.

Ive also constructed an 'ugly' 1:1 choke balun, from 4" PVC soil pipe, and 30ft of RG-213 i had laying about. I had to buy the pipe, but wanted some anyway for making bait stations. Just as well, 'cos its bloody expensive! About 8-9ft of coax is provided as a tail with a PL-259 to connect to the tuner, and about a 6" tail the other end for a connection box to attach the balanced line up to the doublet. The 21 turns of coax are held in place by a number of cable ties fixed through holes drilled in the pipe. Im hoping when finished this balun will prove more effective and less prone to saturation than the 4:1 colins coax balun im currently using, which is made from RG-58. I just need to find a suitable connection box now.

The doublet is performing quite badly. I think its due to the long run of coax currently in use, and the balun, which is at the moment laid on the garage roof and exposed to the rain. I have noticed rain causes tremendous shifts in tuning settings, often to an entirely diferent inductor setting, and sometimes it just won't tune at all! That said, despite the trouble, and by waiting for optimum conditions, i worked PZ5YV, the DXpedition to Suriname! at least i think i did, strange how you get a bit paranoid about these things! and the online logbook isnt working.

Pole Position

Today i had to do some shopping. A trip to the post office to collect the pressure sleeve UHF connectors i had ordered (finally got fed up of poor connections due to trying to solder braid to normal plugs) and to get animal feeds.

Now, i get my animal feed from a place called Hillam Feeds, a few miles away. So, with the car loaded up with sacks of feed, plastic containers etc, i headed back. As i passed a small building site, where some nice looking houses were going up, i noticed a young lad loading short scaffolding sections on a wagon. I slammed on the brakes, reversed back, and went over and asked who the scaffolder was. After explaining why i wanted scaffold poles, he went to talk to his gaffer. The gaffer then phoned the boss, and about five minutes later, told me "a tenner each", so with the help of the young lad i roped two 21ft galvanised scaffold poles onto the roofbars of my Fiesta, handed over £20 and started the careful drive home. Its only when carrying such a load that you realise how bumpy the roads are, and i had to go at 20mph to avoid the poles starting to bounce about. Luckily, the whole journey is over lightly used rural roads. So now im sorted for mast poles! All i need to do now is decide on the actual method of mounting and get the job done, and my 6m and 2m beams will be up in the air.

To that end, getting the pole attached to the house, i had a chat with the chaps at Brymar. Brymar are a satellite TV company, and i had to visit them anyway for a splitter and some sat coax and F connectors, for the wifes small works project of getting DTV into the kitchen. I had to get some self amalgamating tape as well as mines nearly run out, blimey thats expensive stuff, but its a real must have, its either that or Denso, and i dont think the XYL would like me using that! Im now wondering wether to go with the T & K brackets, which i think are a bit too far a stand off, or get some A frame brackets, that spread the load further out, and i think would be less pulled by the wind loading. If it can hold a 1m solid dish up in the wind, i think it can handle a couple of VHF beams!

Theres a hole in my sealant

I finally got around to resizing the doublet from 102ft, as was for G5RV, to 88ft top section. I took the opertunity whilst scared stiff up the ladder to extend the lanyard considerably, taking the end of the antenna well clear of the buildings, and hopefully putting an end to any RFI problems triggering the neighbours security light.

As soon as i had it back in the air and went to test, disaster! nothing would tune right, and 20m (my favourite band) wouldnt work, giving an SWR greater than 6:1 if i ran high power. So, i thought, the line lengths are now wrong, so i went through the calculations and added 6ft of feeder to ensure no band was an odd quarterwave. No change. Hmm, strange. So i inspected all the joints and found one that was corroded. This being the point where the original G5RV matching section line joins the ladder line back to the balun. So, i cut the bad joint out. Still no better. Closer inspection showed one side of the ladder to have black copper oxide on it, hmm, its been wet. I cut it back, and back, and back. I cut out 4ft of line and it was still oxidized. Now, i had assumed that the water had got in at the bad joint, but now the oxidation was on a section that went vertical. So i lowered the whole antenna and had a look at the feedpoint. Nasty. Theres a little hole, right above the end on one of the lines, where the water can get in. And guess what - yes, thats the side thats corroded. All the way down the line.

So it looks like the poor tuning and performance is down to this water ingress. So i have to replace that section of line. Unfortunately i only have 13ft of line left, and the section if much longer, so unless i come up with a better way of routing the feeder, i'll have to buy another roll of ladderline.

All this has come at an awkward time, just as my friend Andy G7PZL is finally equiped for HF and wanted to do on air tests. I couldnt hear him at all, and hes only 25miles away or so. Im considering a Cobwebb antenna for the higher bands, this at least is coax fed. It all depends on what the XYL will let me have. Shes already not happy with me wanting to put two VHF beams up. It would still mean i would need antennas for 40m & 80m, maybe even topband 160m, but i could perhaps get away with a fan dipole for these and coax feed.

Either way, i need to finalise the antenna system before spring, for both HF and VHF, after which no further work can go into them except normal maintenance, likewise the shack. It has to become operational only, no engineering.