Simple Magnectic Loop Antenna

A while back I mentioned my interest in mag loops and proposed at some stage to build an experimental antenna. 

After much searching I finally found and purchased a variable capacitor from my local radio club, I’m not sure of the exact tuning range but I figure it’s got to be approximately 20 -115pf, this should cover me for QRP work, but it obviously limits my power output. 

So now having the copper piping and the variable capacitor I’ve been able to begin building the antenna. As this is purely an experimental project I wasn’t going to make it as neat and tidy as some of the examples I’ve seen on the web. The idea was to build a simple loop connect it all up and see what happens. 

The first issue I had to work out was how to build it, as I had no experience with mag loops what so ever! But after hunting around on the internet I found plenty of examples and a handy calculator tool  to work out dimensions etc.

Getting round bending 9ft x3/4” of copper tubing was a bit of a problem, I had no plumbing tools so I had to have a think as to what I could substitute and eventually used my circular garden water butt which at roughly 3ft in diameter and set against a wall allowed me to squeeze the copper tubing in between the butt and the wall and gently pull the tubing in to a rough circle. It’s by no means perfect but as long as it circular I wasn’t too bothered. 

 It's not exactly round but it will do the job for this experiment!

For the smaller loop (Primary coupling), I used some thinner copper tubing measured length at 1/5th of the size of the larger loop and ¼” width, I could have used the same width tubing but as I had some of the ¼” handy and it was far easier to bend, I didn’t think that for this particular project it would cause any problems. 

The smaller loop threaded through the PVC tubing and ready to be connected to the coax.

Next I mounted both loops on an old piece of 7ft x 1 1/2” plastic tube.  Both copper loops were fed through holes I drilled midway along the length of the plastic piping so that they were held in place. The top ends of the larger loop were then attached with two pieces of thick copper wire and then soldered to the two connections of the variable capacitor. 

 The Variable capacitor connected up to each end of the main tubing

The smaller loop with both loose ends hanging down were also connected by thick copper wire and then via a choc block connected up to the coax cable which in turn is connected to the receiver or transmitter. 

Basically the whole set up is as simple as possible and took all of one day to complete. 

So, results – well I have to say I haven’t transmitted yet but I connected the mag loop up to my OHR100A and had the antenna sitting next to me as I tuned around 20 meters. No question about it as I tuned and peaked the variable capacitor the signals started coming in, it was working! 

Obviously I've got to do some more testing especially having a go at transmitting but so far considering I've never built a mag loop before I'm very pleased.

Heavy Weight K2 Tuning Knob

I recently bought the heavyweight tuning knob for the K2 off Ebay from a Bulgarian supplier. I’ve seen these tuning knobs before either on Ebay or via other Internet suppliers and have been staggered by the price, as much as £60.00. 

This Bulgarian supplier had the dial priced at £36.00 with free postage which I thought wasn’t too bad and so went ahead and purchased. The knob duly arrived well packaged and protected by a foam surround and a thoughtful inclusion of the required allen key. 

First impression of the knob was a well-constructed nice weighty item and I was keen to mount it on the K2 as quickly as possible, but imagine my disappointment when I offered up the dial and no matter how much I pushed it didn’t fit. 

I checked the dimensions, specifically the width which was 6mm but on checking the shaft width on my K2 it was more like 6.2mm!  I checked for any dirt etc within the knob or on the shaft but all was clean; there was clearly a measurement issue somewhere.   

Had I missed something in the small print?   

However the difference was so small all that was required was a 6.5mm drill and a steady hand and I gently removed some excess metal and hey presto the knob fitted neatly over the shaft. A little extra bonus was that the old K2 knob fitted perfectly on to my OHR 100A!

Anyway, I wrote to the supplier asking him if he knew that maybe Elecraft later versions of the K2 had possibly changed the shaft size. "Boris" kindly wrote back and indeed Elecraft had changed the shaft size somewhere along the 7xxx version, he had mentioned it in the small print but of course I had missed it, Doh! 

Never mind all is now well and Boris will make the small print a little larger for dumb people like me!

Repairs to the Mast

The autumn gales have now arrived and after a good summer you sometimes forget how bad the winds can blow round the Cotswold’s. When these gales appear I regularly lower the mast, the cobweb can easily be damaged in the strong wind, so I don’t take the risk and besides it’s fairly easy to drop the mast height and tie everything down.  

Last week we had a really big storm with wind speeds up to 80mph. Thankfully there was no real damage but when lowering the mast in preparation for the storm I noticed one of the collars looked a bit suspect and unfortunately when raising it back up the collar gave way and screw lever broke off. You can see in the pictures where it broke, the rust is a bit of a giveaway!

The broken collar

This particular mast is from a company called Radioizing, it’s 40ft in length and fully retractable, with an all metal design it’s quite sturdy and for the price was a good deal when I bought it some years ago. 

Wear and tear is beginning to take its toll and there looks to be a design weakness in the collars. To replace the broken collar all accessories have to be taken off so I have brought the mast down and obviously removed the cobweb at the same time.

The next collar up (as it should be) but look at the rust!

I’ve ordered a new collar so will have to wait for the replacement before rebuilding and then erecting it back up. But this will also give me a chance to do a quick service of the cobweb. 

The mast laid full stretch but collarless!

The other possibility is to switch cobwebs, by taking the G3TXQ from the attic and see how it performs, it’s also a much lighter antenna so it would be easier to place on top of the mast. I'm not sure how much power the G3TXQ can take compared to the G3TWP, I've easily had 400 watts out, which is useful for the DX, I've got a feeling the G3TXQ is limited to about 200 watts but I'll do some checks. 

 The G3TWP looking a bit lost!

The G3TWP could then be placed back in the attic which might prove an interesting experiment. But until I get the replacement collar there is little I can do, so for the moment I just have to wait.

Magnetic Loops

Time for another antenna project I think, but what to build?

Rummaging around the shed in the garden I noticed I have two 12' copper pipes roughly 1/2 inch diameter that have been sitting doing nothing for a number of years. Since they are not needed for plumbing I’m sure I can put them to good use.

I was thinking about making a small magnetic loop antenna, the measurements seem pretty straight forward  but at the moment I have little knowledge about what variable capacitor will be required and how it’s all connected up. I guess it’s a matter of searching the net and see what I can find.

A quick search has revealed a lot of theory but nothing substantial on building. I prefer something with pictures and an easy explanation to all the “geeky stuff” (not that I’m against it) it’s just I like to see everything laid out in front of me and easy to follow.

If I could build a reasonably small antenna hopefully that would fit in the attic it could turn out to be a fun experiment. Anybody who has details or knows of a website with fairly easy instructions I would be “mucho grateful” if they could let me know. In the meantime I can get on and figure out what band I want to use and see about measuring up the copper pipes.

K2 Update Sunspots and Other Hobbies

Well it's been a while since I last wrote so I thought I'd better give an update with regard to what's happening in M0AUW radio land!

I've been playing a lot with the K2 getting to understand the different filter settings and the manual ATU settings. Setting up the correct filter settings is really important and can alter the operators outlook on how they perceive this wonderful radio. Mucking up the settings can make the receiver sound dull and noisy and you have to be very patient and thorough otherwise you may start wondering why everyone is saying it's such a good rig, when you find it, well, just ordinary!

But once you have spent the time getting everything right it really is a good little transceiver, the receive quality is outstanding certainly matching the old FT1000 MP V although I have to be honest for day to day use I still prefer the FT, I find it much simpler to work, probably because I don't have to mess about with manually adjusting the ATU.

I've learnt that it's not always good to have the preamp turned on, it does tend to raise the background noise. Finding a weak signal and then using the filters can bring up the signal without the need for the preamp, it is really down to just lots of practise and playing with different settings.

Contacts have been good but the DX has been appalling when you take in to consideration that this is meant to be the peak of the cycle, some days there's just nothing going on with regard to DX, unless of course you have a massive yagi sitting on your tower out in the garden! The cobweb is no slouch when it comes to DX nor is the 30m vertical I have but lately it's just been dead which is very disappointing. However I get by and am happy to be contacting various stations in and around Europe with the occassional DX thrown in.

I watched a very good programme on the BBC last night all about the sun It explained about sun spots and radiation patterns and also discussed about a much longer cycle (the 300 year cycle) and the possibilities that we maybe approaching another of these, one of their reasons being the change in the weather conditions over recent years, all very interesting stuff and well worth a view.

Thinking ahead I will definitely be upgrading the K2 to SSB and I have a contact who has the spare option so hopefully we can do a deal and I can install over the winter which will give me something to do.

In the meantime besides the radios I have other things to play with and am in the process of building a touring bicycle for my future attempt at riding the "end to end" run which is John O'Groats in Scotland to Lands Ends down in Cornwall, some 1000 odd miles riding.

I'm quite a keen cyclist not by any means a gung ho speedster but happy to do a 2 hour ride round the Cotswolds on a Sunday morning which keeps me reasonably fit. The plan would be to cycle approximately 50 or 60 miles a day and take in the scenery of the English countryside at a reasonably steady pace.

But like all things it's finding the time (at least 10 free days) to carry out this little jaunt and working out where to stay and what route to take, maybe next year or possibly when retirement is looming!

What would be be even more fun it to do the cycle ride and have a mobile attachment on the bike, hmm could prove interesting!

My Friends Mad Cycle Ride

This  is a completely separate issue but a good friend of mine who has recently retired has taken on the challenge of cycling from John O'Groats to Lands Ends. 

This is a well known cycle route that mad Englishmen take either because they are very keen cyclists or completely nuts, I think my friend is the nutty one! 

Anyway read his blog, it is very funny!

Kierean Whelan's Bike Ride

K2/100 Completed

The KPA100 is now completed and after thorough testing I’m glad to report I’m getting 115 watts out of the K2. 

I have to admit towards the end of the build I was beginning to get a bit tired, I’d taken a lot on but it has been worth it, to build a pristine K2/100 in the such a short period of time cannot be bad. 

I’ve had some ups and downs especially with the PLL oscillator testing which really threw me, but I’ve fulfilled my ambition which was to build my ultimate kit.  

There’s no question if you want a bit of a challenge and something to do during those long winter evenings this is a great kit to build. You have excellent instructions and the knowledge of back up from both Elecraft and the forums should you run in to any difficulties.

Problems associated with these or any kits are normally self administered, e.g. cold solders, soldering bridges or missed components. Rarely do you get a component failure and if by chance you do, Elecraft will simply ship out another to you.

The instructions are extremely good but you must follow them carefully, you cannot jump ahead or miss out pages; you will find yourself open to mistakes which take forever to find and then repair.

I have only one correction in the instructions, that is to include the connectors P3 and P6 in the original build of the K2. These small two pin connectors are  used for connections to the KPA100, they would not effect the K2 if added before hand and it would mean you don't have to remove the bottom cover of the K2, which can be a difficult process.
It’s a real shame when you see the light at the end of the tunnel then you realise you have to open up the K2 bottom cover just to add two pins!

I'm not sure whether to add the SSB option in the near future, knowing me I suspect I probably will, also at some stage I will need an automatic antenna tuner, the SWR on the K2 is very sensitive and using a manual ATU is proving interesting to say the least!

Well I'm at the stage now where I'm going to enjoy my new toy, I will use the K2 as my main radio for the next month, just to get used to it and to see how good it really is. 

I must admit looking at the shack now I'm beginning to build up quite a few pieces of kit. Not sure what my next project will be but I suspect some kind of antenna, I have a nice rotator sitting in my shed doing nothing, maybe I should attach it to a moxon or a yagi!!

KAF2 Installed in to the K2

I’ve now completed the installation of the KAF2 in to the K2 and what a difference on receive, I was pretty impressed with the standard set up but by activating the KAF2 the background noise literally melts away.

I have the optional CW filters fitted to my Yaesu FT1000 MP V and it is extremely good at fishing out those quiet stations hidden by QRM or some other interference, but the K2 matches up and in certain circumstances beats it hands down.

It’s not necessarily the filters, it’s the background noise, with the KAF2 installed in the K2 there simply is none!

Attempting a simple test I matched both radios to a fairly strong 30m CW signal with all the filters switched in. I have to be honest I was amazed at the difference.

The background noise on the Mk 5 was certainly louder although clarity of the CW station was good, it was just you had that what I can only describe as a fish bowl echo to deal with.

The K2 did not have the fish bowl echo; it was just very quiet with excellent clarity, even more incredible was that I could reduce the filters on the K2 and it still beat the FT for clarity and background hiss. No question the K2 wins that particular department.

What's interesting is I can remember when I first bought the FT1000 MP V and being so impressed by the receive capabilities, especially against the old FT 990 I had at the time.  The MP V is a fine radio and I must admit I didn't think its receiver would be beaten by a kit radio costing quarter of the price. Still, I wouldn't sell or swap my FT for anything, the K2 may beat it on receive but that's about it!

The KPA 100 is now under construction and I’ve now reached the first alignment procedure, no big issues yet, but now I have to start connecting the amp up to the K2 and start doing some testing, so things may liven up! Once the alignment has been completed I can start winding the toroid’s and hopefully begin to see the light at the end of the tunnel.

A footnote to my K2 receiver opinions, I've just come off air an hour after writing the earlier post:
I had a QSO with JA4FKX/QRP (Nan, near Osaka) he was transmitting 5 watts using a Yagi. I heard him closing with an Italian station and I thought "what the hell, let's give it a try" So I called him on the K2 with 5 watts going through the cobweb. He came back giving me a 549!  
Distance between us: 9602 kilometers or 5966 miles. 
Don't you just love amateur radio!

Rework Eliminator and KAF2

The audio filter KAF2 has now been completed but not yet installed. 

The kit was fairly easy to build and only took me a day to finish. Besides the KAF2 I have also built the Rework Eliminator which alleviates the pain of removing components from the K2 when installing the various options, it’s a sort of plug in and play which a lot of K2 owners recommend for obvious reasons. 

You simply break off the required circuit and plug it in to the area the option will sit within the K2, this acts as a cover until you are ready to install the option kit in to the circuit. This means when you purchase an extra option you do not have to unsolder any pieces of kit, you can just remove the eliminator and install your new option at will without the hassle of any soldering, a very simple but vital piece of kit. 

My only problem was that the Eliminator turned up late and I was well in to the build of the K2, so I thought better to wait until I’d completed the radio before installing, just means I have to dismantle the main box again and have a play on the circuit boards , but I think I can live with that

K2 Completed

Well the K2 was completed on Sunday afternoon virtually one month to the day from first receiving it in the post.
By Sunday evening I’d had my first QSO with a French station F3MB (Jean in Bordeaux) who gave me a good 589 report. 

 Safely positioned in the Shack!

 

The building of the transmitter went a lot easier than the receiver but I still had a few issues along the way. Sunday morning on the first power test I thought I might have a serious problem as it was only pushing out half a watt no matter what power output I was selecting, something was not quite right.

A quick search on the Elecraft K2 forum and I had the information for a basic power trace of the problem and within the first couple of power checks with the DMM I found a cold solder joint on one of the transistors. A quick touch of solder and a few more checks which produced no further issues I put the K2 back together and hit the tune button, all was well and I was getting good power out in to the dummy load.

My only concern is that I'm having to use a manual ATU which is a bit of a pain when trying to remember each tune and load settings for the different bands. So its either invest in the K2 auto ATU or buy myself something like an LDG auto ATU, well see what happens.

Looking good next to the old OHR 100A

Now I’ve got the two other options to build; the 100 watt PA and the audio filter which hopefully won’t take me too long. I’ve also got the chance to buy the SSB, 20 watt ATU, and 160 meter option from my fellow K2 builder down the road from me. The SSB and 160 might suit but the 20w ATU wont be much use.
I'll see, I may well be "elecraft'd" out by the time I've built the PA and filter!