Interference Solution

Interference Solution

Further analysis of my previously  mention interference problems showed two things:

  1. It’s constant (I monitored it with SpectrumLab for a week) and seems to emulate a pattern of a person turning a heater on and off in the mornings and evenings; and
  2. This was not new, as I looked back to one of my 600m mailing list posts around the same time last year where I mistakenly assumed it was due to a change with my mini-whip.

So in a bid to fix it I started to look at Small Magnetic Loops (SMLs).

Using a suitable SML, in theory I should be able to use it’s strong null’s to block interference. So I went about a few ideas but in the end I basically built the amplifier as per PA1M’s page, however I simply re-used the power supply unit for my mini-whip and went with some different loop designs.

Capture showing effects of rotating SML.

Capture showing effects of rotating SML.

Now I’m sure you’ll agree from the image on the right, that the basic principle of a SML’s nulls is working for me. To explain, I started the capture with the loop oriented such that all was well, then in the middle you see when I rotated it such that the interference came back in. Then, at the end I’ve rotated it again to null out the interference.

Interestingly (albeit not surprisingly) the loops orientation is such that it’s radiation pattern is almost perpendicular to that of my dipole.

So, I’m mostly happy as a result.

However! The receive level is well down on the dipoled. For example, without interference and no pre-amp turned on my receiver used to sit at around S7 (and then s9 when the interference kicked in). However now, with the pre-amp on I struggle to see anything on the S meter. 😦

Building the above amp I did use a pair of 2n5109 transistors to ensure all would be well up on the 20m band. However, I fear the biasing network is not setting enough gain for these guys. So I really need to revisit this – or maybe just go and grab one of the commercial offerings.

Lastly, I originally attempted with a loop that was ~1m in diameter and found that on 20m I pretty well had no nulls. Then I remembered that a SML should be no more than 0.1 of the planned wavelength (so ~0.67m for 14.150MHz). So I setup with a 0.5m loop and that’s when I definitely saw the nulls I was after – albeit with degraded receive performance on the lower bands.

Anyway, when I get a chance soon I’ll provide some pics and hopefully also attempt to increase the gain.


Attempt to setup for 20m – interference

Example of interference on 20m - 14070

Example of interference on 20m – 14.070 MHz

My long term goal here is to have an inverted V for 40m. However the other week I was looking at my 10m vertical in the garage and started wondering what I could throw up in the short term for HF. It then dawned on me that between the eave support for my 2m/70cm antenna and a pole in my back yard for an old arbour I’m pulling down, there’d be just enough space for a 20m dipole!

So last week-end I finally got a basic dipole up, tuned it and the SWR was looking good! I attempted some WSPR and I was happily receiving stations from America and Europe (albeit, my shack computer currently has no network connection – so I was unable to post spots). In return, I could see I was also making the same distance.

However shortly after that I realised this was causing TVI. I thought this was surprising considering it was low power and at 20m, however whenever I transmitted I immediately trigged a ‘No or weak signal’ message on my TV.

Example of interference on 20m - 14070

Example of interference on 20m – 14070

Easy fixed, I wont transmit until the week-end (when I’ve time to investigate and address) and will just attempt to receive some SSTV. But this turned into a rather mediocre result and led me to look closer at what I was receiving. I then realised there was little point fixing the TVI issue as I was going to have trouble even receiving!! The image on the right is what I saw (which is also reflected in the S meter sitting up at a solid 9).

The image was taken at 14.070 MHz as one of the main things that attracted me to 20m was the hope of lots of digital work – and that’s focused between 14.070 and 14.090. But up at 14.230 (the SSTV calling frequency) the image was similar albeit the lines are more straight/constant.

Anyway, I did the normal thing and turned off the power to my house and ran on battery supplies. But the issue persisted – indeed, it didn’t seem to change at all. So I guess there’s some localised interference, but I’m not entirely sure what this pattern might be caused by or indeed what my next choices might be. I’m kind of just taking it as a sign that 20m  is out… But that said, if you recognise this pattern (or have suggestions) please jump on in and leave a comment.

10mComparisonAs a comparison, I thought I’d see if I could tune the dipole up on 10m an see what that looked like. The image to the left shows the result. Further to this though, I was able to happily send and receive WSPR to America as well as the reception of a couple of SSTV images also from America.

So whether that means I cut the thing down to size for 10m and just go with that until I get my proper 40m setup done… I don’t know. Anyway, it’s the end of the week-end so I guess I’ll just have to ponder it a bit.

2m/70cm Antenna Installed

It’s been a bit quiet lately due to life and the many surprises it can bring. However this week-end I was finally able to get my first permanent antenna install complete.

X-50NThe antenna I installed is my dual band (2m/70cm) antenna that I purchased a few years back with the hope that one day it would become my permanent base station antenna. It’s a Diamond X-50N and when I’ve used it in the past I’ve been very happy with it’s construction and performance.

Stats taken from the Diamond Antenna site.

Stats taken from the Diamond Antenna site.

Not long after moving to my new QTH I rushed down to the hardware store and grabbed the fascia mount TV support and bolts and then was keen to get it installed. However, first I wanted to get the access panel done and then realised I needed a bigger ladder – as the install location is essentially two stories up (the antenna is now sitting ~6m above ground).

Anyway, a hire company came to the rescue and all worked out well this week-end. And with the access panel in place, it sure made the cabling very straight forward. Although, I do have a goal of eventually having some semi rigid cable for this, but for now RG-58C/U is doing the job (albeit I should only be losing about 2dB and 4dB, and this is really only for local simplex and repeater work).

I’ve only had one contact with it so far, but that was as a result of the first (and only) CQ I put out on 146.500. Reports were good from over in Bellerieve (5/7 – loud and clear) and I can happily trigger all the local repeaters on 2m, and I only attempted one on 70cm – need to try more. So, it seems a good result and I look forward to trying it out more soon. (Plus, I’m going to try some WX Satellite reception here – though on Windows this time – and see how it goes compared to my efforts in VK1 – although it still will be a sub-optimal antenna and receiver for that).


Access Panel Complete

A week-end or so back I completed my access panel with it’s full complement of bulkhead adapters and dust covers. Unfortunately  I’ve been struggling for any good light on it though, so I’ve just taken some rough photos with my phone at late dusk (ie. low light – unfortunately.)


I went with 5 N sockets in the end. That was because five fit the space easily – and matched my aspirational antenna setup – and I went with N sockets as I figured they’ll meet almost anything I’d plan to do. I did consider having one or two BNC or SO-239 sockets, but with N connectors being spec’d to around ~11GHz I figured that’s the best bet for flexibility.


I’ve not had a chance to really put the panel to much use yet, as next on my list is to setup my external antennas. However, I do have my mini-whip connected and happily achieved a few spots on 40m with ease (indeed, VK1KW was booming in at +5). Now I’ve got it just sitting there hoping to maybe pick up some MF – we’ll see.


The idea of the access panel I definitely didn’t come up on my own. I was inspired by what I saw VK1OD had done, and so asked for some further details and came up with the implementation above for my purposes.

New Portable Antenna

On the week-end I tested my new portable HF antenna – a simple doublet targeted at 40m. That is, a half wave dipole fed with parellel feeder.


My previous portable antenna was an end fed inverted V – targeted at about half a wavelength of 40m. However I was finding that this antenna was highly dependent on a good earth connection, and sometimes portable this was a struggle.

With the doublet being feed with a balanced line, it’s a bit more tolerant of poor earth and varying conditions in general. So for portable, it definitely seemed a better fit.

Further, I saw it mentioned on the VK SOTA mailing list and after a bit more reading came across the NorCal QRP Club Doublet made from some 4 strand computer ribbon cable. I didn’t have any of that lying around, but I did have a roll of some figure 8 speaker cable from Jaycar.

I was concerned about the weight of this cable (especially compared to the above mentioned ribbon), but it was on hand and something I could try pretty quickly. In the end although it’s a bit heavy, the squid pole seemed to tolerate it – but it could be good to do a lighter version and maybe use this one more in a tree.



For the dimensions I kept it simple. My squid pole is 9m, so that was the length I chose for the feeder section. Then the idea was for it to be a half wave dipole for 40m. Having two legs from the one section (once split down the middle – being figure of eight cable) I simply needed another 1/4 wavelength of cable added to the 9m.

This worked out at around about 9m plus 10.56m (aiming around 7.1MHz, but not too precise). To this, I also added 4cm to allow for folding back over of the end of each leg to form a loop for attachment. So all up, I had 9m plus 10.6m giving me 19.6m of wire to cut.

Once measured and cut, I split the 10.6 down the middle and folded back the ends and held in place with cable ties and added some support rope/string.


For the middle, I  wanted to add some cable ties both to ensure it didn’t split further and also to add a larger cable tie as a support mechanism.


Finally, at the end of the feeder section I added a couple of crimp connectors to feed into the balance connection on my portable antenna tuner.


The result was good, and worked first go when setup in the backyard with no earth connection. With the parellel feeder having such a small gap, it’s only intended for QRP. But with QRP (<5W in this case, and approaching 2.5W) I happily reached NSW, Northern Victoria, Melbourne and North West Tasmania with only a short period of testing in the morning and then afternoon. (From my backyard at QE37pa.)

I also attempted tuning it on 80m (but not attempting to contact) and found that was possible, albeit with a reasonably narrow bandwidth. But that said, it was easy to tune on 40m and 80m where my previous end fed inverted V was not – unless a good earth was present.

So, a good result and I’ll definitely be using this as my portable solution going forward. Although, I may attempt to get some lighter cable and make another (maybe some simple bell cable).

Just a finishing note – Above I detail that I simply cut this antenna based on calculations rounded up for 7.1MHz and then didn’t attempt to tune and recut for best SWR. This was because seeing I plan to use it in many varying locations and always with a tuner I thought I’d just keep things simple. If it was going to be a permanent setup, I’d do it differently. But mainly, I had limited time and just wanted to give it a go. My next one I may take out to a nice flat oval and set it up and then tune before finalising cable ties etc – and may also trim the feeder to best fit based on squid pole droop.


Access Planel Installed

Today was somewhat productive with the installation of my access panel. I now (almost) have a means of getting antennas into my shack, and now have an earth connection into where the radios are.

The panel is a simple 2mm sheet of aluminium, and on it I’ll be mounting a collection of bulkhead N adaptors. Currently the earth connection is only to one of my earth rods, but I’ll grab some more earthing cable as well to complete the job.

Some photos. First up, the wall after the brick was removed.


And then after the panel and earth connection was added.


And a view from inside.


Bit by bit

Well, bit by bit I’m getting settled into my new place and am finally seeing a return to focusing on radio. I’m still yet to really unpack my garage, so my radio and electronics gear is still mostly in boxes.

That said though, I do have my portable FT-817 setup on hand and so I recently set this up to participate in the QRP-Hours contest. I was impressed that with my very basic setup with minimal earth what I was able to achieve – and hear! It gave me confidence that HF operation from my new QTH going forward will have real potential.

To that end I’ve started planning my antenna setup and other bits such as earth.

Based on measurements, I’ve confirmed I can fit a full size inverted V dipole for 40m and have started planning the build of this. The final structure will take time – as time and money allow, however bit by bit I’ll get there. As I do, I hope to have interim setups along the way.

But, starting with the basics, I’ve now put some ground rods in. This was one area that was really hurting me with my portable setup, so it was the first cab off the rank.

I basically placed two ground rods in inside nice submerged covers so that I could get them further down and also provide for a nice and tidy look and a bit of a reduction of a trip hazard. They’re about half a meter apart and I’ll connect them both together and then have a wire up through the wall on the other side of which will be my setup.


In addition to putting these in, I also put an eyelet at the top of my ~8m mast and I think I might temporarily erect that and run a 40m inverted V dipole as a bit of a trial – now that I have a better ground connection.

Also, I have grabbed myself a TV mast to mount on my fascia for my X-50N antenna for 2m/70cm FM work – although, I’ve also got my 2m dipole I plan to mount on it for basic SSB support. Thing is, this roof is higher than my previous single storey abodes, so I now need to hire a bigger ladder so that I can get up there.

Finally, I’ve returned to my morse code training. I’m really keen to get that happening again, and still have visions of using that on LF back to VK1 and especially now with the new (easier) band allocation. I did find that having learnt on with the keyboard, I stuggled to copy morse with a pen and paper. I actually wonder if by learning it on the keys the association I’d mainly made was that of a keystroke and not a specific letter.

So my practice is now pen and paper based with Ham Morse on my iPhone. I figure being able to copy with pen and paper is a bit more practical, and should easily also translate to typing later on. Once I get past that stage, I can again return to sending practice.

That’s all for now, hopefully I’ll come back soon as I get my station setup bit by bit.

P.S. Another thing I’m hoping to do soon, is build a simple regenerative receiver for 40m. Never built a receiver (well, other than a crystal radio), and regens just seems like fun in a retro kinda way. But this will mean I really need to unpack my boxes and get access to my electronics bits.

Small Magnetic Loops

Of the various types of antennas I've built, I've never built a magnetic loop. It always seems like there's a bit of magic involved and relies on hard to get suitable air spaced variable capacitors.

By magic I mean people rarely give exact dimensions; and to find a suitable air spaced variable capacitor is not just a case of going to one of your regular electronic parts suppliers. However, I've seen VK3YE play with magnetic loops a bit lately and I know they're good for their small size, so I think it's time. Better yet, I believe they match a need I have.

This week-end I finally got around to starting to build my Softrock Lite II kit I purchased back in (I think) March – when I was still in F call (so RX only was the only sensible option from a license perspective). Seeing it's RX only (and due to thinking my shack computer may not have a stereo line in) I'm thinking it could be cool to just setup inside on my main machine. For that though, I need a nice simple antenna that I could have inside and thereby needs to be relatively small. (Oh, and I'm going for 40m.)

In my search for small magnetic loops I came across the G4ILO Wonder Loop. This is close to what I need, and could be fun to build and then use with my FT-817. Further, I also like the simple SWR bridge that is being used – may just build one up from scratch.

I like the way he explains figuring out the dimensions (and indeed the information that it's a simple 5:1 ratio between the loops), and I've also found an Australian supplier of variable capacitors. It's the local Jackson Brothers suppliers that have been advertising in AR Magazine for years but their website never worked so I left it there. But I finally took a punt and emailed them to see if they had a catalogue and price list. Turns out they do and were very prompt in it getting it to me.

So now I have a known supplier of high quality variable capacitors, an idea about dimensions for magnetic loops, and a need. All I need now is time! 🙂