For many radio amateurs, myself included, being able to build our own kit – be it receivers, transmitters or test equipment – has always been an important part of the hobby. One important component of many of these items has always been the polyvaricon or small AM tuning capacitor. These are used to tune radio receivers, or as part of a low power / QRP antenna matching/tuning unit (AMU / ATU). Unfortunately it now appears that they are no longer being manufactured and whilst there are a few left on the surplus market, supplies are likely to come to an end. It seems that in this age of digital radios and push button tuning there is now no call for them – who listens to AM radios anyway? Of course there are those of us (radio amateurs) who will always want some form of small tuning capacitor such as this for the radios that we build, won’t we?
Small AM tuning capacitor
Of course being resourceful amateurs we will soon find an alternative (I am sure). One possibility of course is to use small trimmer capacitors but then the ease of adding a small tuning dial would be gone. This would bring the need for holes drilled in cases above said component and the use of trimming tools to tune them. Not the easiest of ways to retune your receiver or “net” your CW contact.
Something new arrived in the postbag the other day – an Alinco DJ-G7 three band handheld transceiver. Operating on 2m (145MHz), 70cm (433MHz) and 23cm (1296MHz) plus a wide RX scanner from 0.53MHz – 1299.995MHz although it is bblocked on the cellular/mobile phone frequencies for obvious privacy reasons.
Anyway, I unboxed it, fitted the battery (Li-Ion) the hand strap and belt clip and turned it on to see what it could do. Obviously, the battery wasn’t fully charged so any transmitting would have to wait but, on tuning through I did manage to pick up some nearby PMR stations which seemed promising. It also came with a nice desktop charger which I made use of and was surprised at just how fast it charged the battery. The manual states that using the supplied charger the battery can be charged from flat in 3 hours, I made the initial charge in about one.
Personally I live in a very bad place for VHF amateur radio, let alone UHF so I was pleasantly surprised when I sat the DJ-G7 on the coffee table the next morning, scanned through 2m and voices suddenly erupted from the speaker. It was G4VUA (Alan) from the next village running a local(ish) net. I picked up the set and called in and, lo and behold, he replied to me. Not bad from a little handy sitting in the living room. All things considered though he does have an advantage of height above me.
Anyway, how clean is the signal? I tuned it to 1.2965Ghz and with only the supplied rubber antenna fitted, checked the output against my spectrum analyser. The results were spot on – a lovely clean signal with no harmonics detected. Well done Alinco – this one looks like a winner.
Moving on to other matters, conditions both on HF and VHF have improved of late. There have been numerous sunspots appearing and this has led to some late summer sporadic e propagation on both the higher HF bands (15, 12 and 10m) and the VHF bands of 6, 4 and 2m. I suppose this was ideal for this weekend which was the Worked All Europe DX Contest. However, myself, I made a few CW contacts with EO25UA, EO25UD, ZS9AZ and EM25HQ to name a few. I also collected a few contacts on JT65.
Also, a friend of mine – Stefan, DO2JAX, has been operating from a holiday location as OZ/DO2JAX. After a week I managed to work him yesterday on 14.317.5MHz. H ewill be active from this location until the 19th August so, if you hear him, give him a call. He is only operating SSB but can be found on all bands at different times.
Till next time.
73 DE M0CVO
Due to one thing and another it seems that I have not had a lot of time on my hands to do much radio activity for a while. The sun was spotless for some time during the month of July and conditions on HF literally bottomed out. Luckily this all seemed to change in time for the IOTA Contest on during the weekend of 30 – 31st July. Suddenly there were spots on the sun a decent MFI and all bands opened – right up to 2m. There were intercontinental contacts to be had throughout the HF bands up to and including 10m (28MHz) and quite a few 6m hops although these were probably more down to sporadic e’s rather than multi-hop F2 Layer propagation.
Anyway, during the month I have been experimenting with antennas for 23cm (1297MHz) and 13cm (2321MHz). I have looked at various designs from the double quad antenna, More details of which can be found HERE to the slot antenna, which can be read about Here and the IFA Patch Antenna, which you can read more about HERE. I finally settled on a version of the IFA antenna as this was easy to etch onto a piece of single sided PCB with an FR-4 backing.
Using MiniVNA Tiny to determine properties of 23cm IFA Antenna.
Once I was happy with it I 3D printed a case for the antenna to fit into and checked that the VSWR readings remained below 1.5.
IFA Antenna in 3D printed case.
I also looked at the Vivaldi antenna details of which can be found HERE which would make an interesting broadband antenna that could be used to feed a dish, but decided against it at present.
On Friday 26th July I was lucky to receive notification that I had won a pair of RF Solutions LoRa modules in an online competition. I promptly received these on the Saturday and set about trying to work out what to use them for. They are effectively a voltage controlled pair of transmitters/receivers and can be encoded to work as remote controls, provide remote networking, remote switching or act as remote sensors. The range is up to 16km using spread spectrum technology at 868.5MHz.
The RF Solutions Ltd Gamma LoRa pair
I am currently experimenting with them as a remote wireless sound activated switching system. More details on this at a later date.
Sound Activated wireless switch..
I read with interest a letter in the latest issue of Radcom entitled “HF Conditions – If only!”. In it the writer laments over the lack of DX opportunities available on a daily basis as compared to how it was when he was an SWL 40 – 50 years ago. I could also speak of similar things. When I got my 1st licence in the late ’90s (VHF only B licence), we were at the peak of Solar Cycle 23 and 144MHz was like 20m is nowadays and there was always DX to work. When I took the 12wpm CW test and got my current HF licence in 2000 we were still being blessed with excellent HF conditions and I managed to work amazing DX suing just a base loaded magnetic mount antenna for 15m sat on top of the ATU inside the shack – at night too! The peak of solar cycle 24 was nothing to write home about though and the peak has now passed.
The above two graphs represent Solar Cycle 23 and Solar Cycle 24 for comparison. It can be seen that at the peak of cycle 23 (2000) we had a daily sunspot count of approximately 120 whereas at the peak of cycle 24 (2014) the daily sunspot count was closer to 80. The lower number of sunspots results in more coronal holes in the sun which lead to masses of plasma being ejected towards the earth, resulting in more geomagnetic storms (aurora). This in turn gives rise to some enhancements in VHF (50MHz, 70MHz) but poor conditions on HF.
Looking back further to Cycle 22, it can be seen that the peak was even higher with a daily sunspot count above 150. If this trend continues could it be possible that we are heading for another Maunder’s Minimum where there will be no peak for the complete cycle? Will this mean a total flattening of the HF conditions? It certainly would spell bad times ahead for the higher HF bands above 18MHz. Fingers crossed it won’t come to that and our local star will become a little more active at it’s next cycle peak in 2020/21.
I have been rather busy of late so haven’t had so much time to play with anything radio. I did, however, manage to pop into the local antiques dealer (Notions) and take a look around. Amazing what fascinating stuff you can find in these places. What I did find (and purchase) was three moving coil meters (milliamperes and microamperes) in Bakelite cases. One dates back to WW2 and was for military use and the other two are just post war. All are made by English manufacturing companies (unfortunately no longer in existence) with the quality one would expect from this era.
This one is of interest in that not only does it have a more visible dial and a manufacturer’s name – Crompton Parkinson Limited – it also has a completely clear cover enabling the workings to be seen. The internal resistance of 5Ohms is clearly marked on the front so this can be included in calculations for power and current. Admittedly, with a full scale deflection at 15mA you are not going to be testing any high power apparatus with this.
Researching Crompton Parkinson Ltd, I discovered that Crompton & Co. was a lamp manufacturer founded by R.E.B. Crompton in 1878 and F & A. Parkinson Ltd. was a successful electric motor manufacturing company. They also purchased Vidor Batteries – a manufacturer of flashlight and radio batteries – and Burndept Wireless. If you follow this link: Wireless World 1925 it will take you to a pdf copy of a page from Wireless World, September 30th 1925 describing some of the valves made by Burndept.
Well, yet again I have found myself pushed to make time to spend on the radio. Looking back through the pages of my log book I see many QSOs using CW, the occasional JT65 and even more infrequent PSK31 or PSK 63 one. J3E seems to be a tad rare (I count about 5 during this year so far. I must admit, I do prefer to use the key these days and find that I can get my signal so much further with so much less effort and power. Yes, I spent my money and bought the MD-200 desk mic from Yaesu to accompany my FT-DX1200 but it sees so little use. Aesthetically it does look nice though.
Yesterday I was pleased to manage a QSO with JT1CO in Mongolia for a new DXCC country. This was using 90W of CW into the MQ1 mini-beam on 15m (21MHz). I also managed a couple of Russian contest stations on 15m yesterday. I must say, it is good to hear some of the higher bands opening up again. I tried 12m and 10m but the only openings on these appeared to be between stations near the equator and nothing was heard this far north. the 50MHz (6m) band should be coming to life soon with the sp-e season but the SFI is still too low for it here and for the brief period that it is open most of us will be at work or otherwise engaged when the real DX is happening.
Earlier in April I managed to work many of the Yuri Gagarin special event stations on CW celebrating 55 years since his 1st space flight. Following that I managed several of the HG225 stations for Samuel Morse. I didn’t get all of them though so no award for that one. I did receive my CQWW CW award for my entry into last year’s contest though which is now hanging proudly on the shack wall. Maybe it is not the highest score in the world (#6 in the UK) but for 5W into a wire dipole I was pretty pleased with it for a first attempt. Single Op QRP Unassisted.
I have also been busy designing my next project. 1st prototype boards have been etched – now I just need to cut them to size and drill them. The latter will require a very small drill bit (0.6mm) and either a steady hand (ahem) or a drill stand. I do have a drill stand so this will probably be the way. I am attempting to build a transceiver in stages to cover the main amateur bands (40, 20, 15 and 10m). The oscillators used are simple Colpitts form and the next stage is the buffer and keying circuit. The boards are pictured below for the 2nd stage. I shall then move on to final amplifier (to 5W) and band pass filters for each band.
It has been a bit of a rough ride lately for my radio antics. Last weekend was the international WPX contest which I was looking forward to being involved in. Unfortunately we also had an issue with Storm Katie – a deep low pressure system with extremely strong winds and heavy rain. So the antenna mast was lowered and then luffed over and tied down to protect it against the weather.
Therefore I was, unfortunately not able to take part.
However, whilst it was down it did give me the opportunity to tighten up a few nuts and straighten my 2m Yagi – was pointing in the wrong direction.
It was the 25th March before I had the chance to raise the mast back up to vertical again and without extending it fully (half height) I managed a quick QSO with E74X on 20m CW. Looking at the log book I haven’t really had much chance to get on the air much – SN7D on 26th (J3E), LZ1QI on 29th (CW), YU7MK on 31st (PSK63) and then RW55YG (Yuri Gagarin Special Event) on the 1st April using CW at 30wpm. Not a speed I use very often but glad I can at times.
The mast back upright clearly showing the M0CVO Antennas 1:1 BALUN used at the feedpoint of the MQ-1 mini beam / hybrid quad.
I have been spending some time (whilst the mast was down) designing a few little QRP circuits. Amazing what you can do when you look in the shack junk box and find a few spare components. You may hear some faint CW populating the airwaves around 7.030MHz (+-) with my call latched onto it. This is less than 1W (about 500mW) so not sure if you will hear me but please do listen out. I promise to keep it slow (straight key around 12 – 14wpm). More on this one another time though.
Have the gas engineer round now to service the boiler so will sign off and say 73. Till next time…..