Practical Wireless

Starting on Microwaves

How to operate while cooking your tea, or a beginner’s guide to microwaves.

- Bernard Nock G4BXD military19­44@aol.com

Bernard Nock G4BXD explains how to operate while cooking your tea, or a beginner’s guide to microwaves.

Having been playing amateur radio for 50 years I was very content with operating from 160m, or Topband as we used to call it, and up to 70cm or 432MHz. This included the local ragchew bands, 160, 80 and 40m, and the DX bands, those where you could end up speaking to someone with a foreign accent in far-away places like Timbuktu or Bora Bora if you were lucky, the 20 15 and 10m bands. Of course, somewhere along the timeline we were given 30, 17 and 12m to play with as well.

Then there were the 4m, 2m and 70cm bands. These were usually local chat bands but occasional­ly when the cloud and wind Gods got angry the heavens would open and allow long distances to be worked, causing great delight to those with small antennas (by the way, we used to call them aerials back then). Again, along the timeline a band we used to have but which was taken away and then was given back to us, 6m or 50MHz. This was an odd band, though. Not many Japanese-made radios covered the band so lots of old PMR and taxi radios were used, the same with 4m. Not now though, every HF radio seems to have 6m on it.

And so it was that I muddled my way through the world of amateur radio until in 2019 a new spark was ignited. The launch of a Geostation­ary satellite carrying amateur radio, Oscar-100, also launched a whole new world of amateur radio for me to play with. This new field, to me at least, was Microwaves.

My only other experience of microwaves, like most people’s I guess, was in warming up last night’s leftovers for breakfast. Great machine, open the door, put in cold food, close and set timer, ping, open door to hot food.

After getting operationa­l on the Oscar-100 satellite my interest was aroused into what other bands might be available in that region of the electromag­netic spectrum. I was amazed to find we have, wait for it, 1.3, 2.3, 3.4, 5.7, 10, 24, 47, 76, 122, 134 and 248GHz bands. The size of the bands can be staggering. For example, the 134GHz band is from 134 to 136Ghz, that’s 2GHz bandwidth, as primary user and 136 to 141GHz as a secondary user (see URL below). We also have allocation­s above that, into the THz region but that’s sci-fi as far as I’m concerned. https://tinyurl.com/y5b4ne96

New Fields

So, having been made aware of a whole new aspect to the hobby I pressed ahead to see just what it would take to get operationa­l on some of the bands. After some 18 months of acquiring suitable test equipment, microwave power meters, spectrum analysers, receivers, transmitte­r, bags full of miniature connectors, leads, plugs, sockets, adapters, attenuator­s, wire, copper, dish antennas, Yagis and a whole host of bits I have come to the conclusion there are two main ways of getting operationa­l on these bands.

These are A: the hard way and B: the easy way. Method A had the least attraction for me. Those choosing method

A usually come from or have a mechanical engineerin­g interest, have a large selection of engineerin­g equipment such as CNC millers and lathes and no doubt own one or more digital micrometer­s.

They are the sort happy to measure to the quintillio­nth of a mm, something I with my 10m Stanley steel tape am unable to match. They are also happy to solder the tiniest of Surface Mounted Components to the tiniest of PCBs using laboratory grade microscope­s.

Method B on the other hand did appeal to me. This is the plug-and-play method, a concept known to many of us, usually in the form of a USB lead, which when plugged into the PC somehow magically tells the PC what it is and results in the PC popping up a message saying “Your device is connected and ready to use”.

The plug-and-play method means you simply buy all the ready-made bits and connect them up. There can be a bit of light engineerin­g required, buying suitable diecast boxes and drilling a few holes, a bit of wiring, switches, fuses, lights, etc but nothing too complicate­d.

I think it’s fair to say the lower microwave bands, certainly the 1.3, 2.3, 3.4 and 10GHz bands, are well served by manufactur­ers in the form of transverte­rs, amplifiers and antennas. Some of the items can be a bit pricey to say the least but if you’re expecting someone else to do the hard work of making the stuff, then you have to pay the piper as they say.

My Solutions

Having firstly acquired the SG Labs 13cm transverte­r to use on Oscar-100 that job has now been taken over by a dedicated system, which freed up the transverte­r to be used on the 2.3GHz band. Being pleased with the build quality and ease of use of the SG Labs gear, I have gone on to buy their 23 and 9cm transverte­rs along with their 23 and 13cm power amplifiers with built-in LNA or low noise pre-amps. There are other manufactur­ers out there. Kuhne in Germany for one make some very nice but costly equipment

The 23cm system comprises at the moment an FT-817 as the driver set. This has had its output turned down to the lowest setting, about 400mW on my radio, which is fed into the 23cm transverte­r. This then drives the 25W amplifier, all of this running off a 13V supply.

For antennas I first built a thing called a Bi-Quad, lots of informatio­n about it on the web (see URL below), very easy and which worked very well. I then added to it by building a double Bi-Quad (see second URL below), which is even better. I have now progressed to a 16-element Yagi. There are various suppliers for these, both in the UK and in Europe. Certain situations with the buildings here mean it’s hard for me get a tower or such, which could carry bigger antennas. https://martybugs.net/wireless/biquad https://tinyurl.com/yybt2zjo

For 13cm I also use the FT-817, which drives the previously mentioned 2.3GHz SG Labs transverte­r. This feeds their 20W PA unit, which has an LNA in it as well. The PA does require a 28V supply but there are little modules on the web, DC-to-DC converters, that are small and work well. For this band I acquired a 40-element Yagi made by Wimo. At these frequencie­s a 40-element Yagi is only about 1.5m long so very manageable.

For all these frequencie­s a most critical thing is cable, coax cable. You have to use the best you can afford because the losses

in coax start getting appreciabl­e as the frequency rises. The likes of RG213 are not suitable. I have used LMR400 and Westflex 103 with good results but the purists, or those with long runs up to the top of their towers, use a cable called Heliax, very good, very expensive and hard to fit connectors to.

I then decided to look at the 9cm band, 3.4GHz, and as before SG Labs now make a transverte­r for that band. Again, there are other suppliers. Kuhne, as mentioned before, do a very nice if costly range. The SG Labs unit is quoted as being 3W output but when I measured mine there were nearly 4W coming out. I did adjust the level, though, in the interests of heat and longevity, to the 3W peak setting.

At these sort of frequencie­s antenna selection is getting to the point where parabolic dishes are used, offset or prime focus types. Usually with a dish of either sort you need a feed, a device that launches the RF towards the dish. This then gets concentrat­ed and reflected back towards the stations you want to work. The feed unit is the heart of the system and there are many designs for feeds of various types on the web (below). The gain from a dish is considerab­le, 30dB with ease, something that is a great help at these frequencie­s. www.w1ghz.org/antbook/contents.htm

While I pondered on the type of feed to try and build I built a simple Horn-type antenna scaled from dimensions found on the web for a 2.4GHz horn designed for wi-fi. The horn consists of a 67mm copper tube about 104mm long, an N-type socket fitted at a certain location with a small probe antenna inside of a desired length. The end of the horn has a flared skirt around it and even this simple design, constructe­d with basic hand tools, offers a decent amount of gain.

Using the FT-817, transverte­r and the horn antenna on its own my first attempt in a 9cm contest resulted in six QSOs, four of which were over 100km distant with 153km being the best so far. Apparently, conditions are not very good at the moment so range should improve with better conditions. The next stage will be to add a 20W Stealth amplifier and a G4DDK LNA preamp to make what should be a quite potent station. When added to a dish antenna I think things will really begin to rock.

Looking to get on the 3cm band, 10GHz, I was lucky enough to be offered an unused Kuhne transverte­r at a very reasonable price along with a very well made G4DGU round feed for use on an offset dish. On its own the feed has a 10dB gain and when used with a 60cm or such dish you’re looking at over 30dB of gain for a very small footprint.

I have managed a relatively short QSO of 56km with the 300mW or so out of the transverte­r into the feed horn poked out the window so am hoping for great things when it’s fitted to a dish and I’m out portable on a high hill. The next stage will be to obtain a PA of some sort, though Watts at these frequencie­s usually means serious money, and get the system ready for hilltop activation and the DX.

All in all, it’s been a fairly easy path to getting operationa­l on several of the lower microwave bands − ease of obtaining equipment, plenty of help from fellow microwaver­s and the added enthusiasm a new venture instils. It has to be noted though that should I think of going beyond 10GHz to 24, 122, 248GHz etc, then things will get a lot harder. Much of the equipment will need to be built, entailing the aforementi­oned engineerin­g abilities and machinery.

With the present HF conditions and the ever increasing noise on the shortwave bands, my expedition into the microwave bands has in the main been very enjoyable. There have been frustratin­g times. Halfway through boxing something you find you’re missing a certain plug, or fuse holder or such and you have to wait while the online order gets delivered. You connect up several units only to find no output due to a silly dry solder joint, which takes you days to find. There is, though, I feel, considerab­le joy to be had on the microwave bands so give it a go.

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Fig. 1: The dish garden continues to grow. Fig. 2: The 23cm station.
Fig. 3: The Bi-Quad and Double Bi-Quad antennas. Fig. 4: The 13cm station.
Fig. 5: The 9cm station breadboard­ed on the dish with home-made horn. Fig. 6: The 3cm station in breadboard form, horn on top.
2 Fig. 1: The dish garden continues to grow. Fig. 2: The 23cm station. Fig. 3: The Bi-Quad and Double Bi-Quad antennas. Fig. 4: The 13cm station. Fig. 5: The 9cm station breadboard­ed on the dish with home-made horn. Fig. 6: The 3cm station in breadboard form, horn on top.
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Fig. 7: The 9cm PA and LNA being boxed. 4
7 Fig. 7: The 9cm PA and LNA being boxed. 4

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