uhf

18 Articles

The $50 Ham: Entry-Level Transceivers For Technicians

March 15, 2019 by 95 Comments

Last week , I covered the ridiculously low barriers to entry to amateur radio, both in terms of financial outlay and the process of studying for and passing the FCC examination. You’ve had seven days, so I assume that you’ve taken the plunge and are a freshly minted amateur radio operator. The next big question may be: Now what?

We briefly mentioned the image that ham radio is a rich old person’s hobby, and that reputation is somewhat deserved. For ham gear, there really is no upper limit on what you can spend. Glossy brochures and slick web pages hawk transceiver bristling with knobs and switches and loaded with the latest features, all of which will probably be obsolete within a few years when the Next Big Thing comes along and manufacturers respond with new, must-have models – looking at you, ICOM IC-7300. It’s no different than any other technology market, and enough people fall for that marketing to make it a going concern.

But thankfully, while there is no apparent ceiling on what you can spend on ham gear, there certainly is a floor, and it can be very, very low. Our $50 budget can go quite a long way to getting a new Technician on the air, if you’re willing to make some compromises and can forego the latest and greatest for a while.

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Long-Range RFID With Feedback

January 17, 2019 by 24 Comments

Not long ago, we published an article about researchers adding sensor data to passive RFID tags, and a comment from a reader turned our heads to a consumer/maker version which anyone can start using right away (PDF). If you’re catching up, passive RFID technology is behind the key fobs and stickers which don’t need power, just proximity to the reader’s antenna. This is a much “hackier” version that works with discrete signals instead of analog ones. It will not however require writing a new library and programming new tags from the ground up just for the user to get started, so there is that trade-off. Sparkfun offers a UHF reader which can simultaneously monitor 25 of the UHF tags shown in this paper.

To construct one of these enhanced tags, the antenna trace is broken and then routed through a switching device such as a glass-break sensor, temperature limit switch, doorbell, or light sensor. Whenever continuity is restored the tag will happily send back its pre-programmed data, and the reader will acknowledge that somewhere one of the tags is seeing some activity. Nothing says this could not be applied to inexpensive RFID readers should you just want a temperature warning for your gecko terrarium or light sensor to your greenhouse‘s sealed controller.

Thank you, [Mike Massen], for your tip on RFID Doing More Than ID.

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Retrotechtacular: Information From The Days When Colour TV Was New

September 12, 2017 by 19 Comments

By the time colour TV came to the United Kingdom, it was old news to Americans. Most of the viewing public on the Western side of the Atlantic had had the opportunity to see more than black-and-white images for years when in 1967 the BBC started transmitting its first colour channel, BBC2.

For Americans and continental Europeans, the arrival of colour TV had been an incremental process, in which the colour subcarrier had been added to their existing transmission standard. Marketed as “compatible color” to Americans, this ensured that their existing black-and-white TV sets had no need for replacement as the new transmissions started.

The United Kingdom by contrast had been one of the first countries in the world to adopt a television standard in the 1930s, so its VHF 405-line positive-modulation black-and-white services stood alone and looked extremely dated three decades later. The BBC had performed experiments using modified round-CRT American sets to test the feasibility of inserting an NTSC colour subcarrier into a 405-line signal, but had eventually admitted defeat and opted for the Continental 625-line system with the German PAL colour encoding. This delivered colour TV at visibly better quality than the American NTSC system, but at the expense of a 15-year process of switching off all 405-line transmitters, replacing all 405-line sets, and installing new antennas for all viewers for the new UHF transmissions.

Such a significant upgrade must have placed a burden upon the TV repair and maintenance trade, because as part of the roll-out of the new standard the BBC produced and transmitted a series of short instructional animated films about the unfamiliar technology, which we’ve placed below the break. The engineer is taken through the signal problems affecting UHF transmissions, during which we’re reminded just how narrow bandwidth those early UHF Yagis must have been, then we are introduced to the shadowmask tube and all its faults. The dreaded convergence is introduced, as these were the days before precision pre-aligned CRTs, and we briefly see an early version of the iconic Test Card F. Finally we are shown the basic procedure for achieving the correct white balance. There is a passing reference to dual-standard sets, as if convergence for colour transmissions wasn’t enough of a nightmare a lot of the early colour sets incorporated a bank of switches on their PCB to select 405-line or 625-line modes. The hapless engineer would have to set up the convergence for both signals, something that must have tried their patience.

The final sequence looks at the hand-over of the new set to the customer. In an era in which we are used to consumer electronics with fantastic reliability we would not be happy at all with a PAL set from 1967. They were as new to the manufacturers as they were to the consumers, so the first generation of appliances could hardly have been described as reliable. The smiling woman in the animated film would certainly have needed to call the engineer again more than once to fix her new status symbol.

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Fine Business, Good Buddy: Amateur Radio For Truckers

August 25, 2016 by 51 Comments

Summer is the season for family road trips here in the US, and my family took to the open road in a big way this year. We pulled off a cross-country relocation, from Connecticut to Idaho. Five days on the road means a lot of pit stops, and we got to see a lot of truck stops and consequently, a lot of long-haul truckers. I got to thinking about their unique lifestyle and tried to imagine myself doing that job. I wondered what I’d do hour after long hour, alone in the cab of my truck. I figured that I’d probably just end up listening to a lot of audio books, but then I realized that there’s a perfect hobby for the road — ham radio. So I decided to see how ham radio is used by truckers, and mull over how a truck driver version of me might practice The World’s Best Hobby.

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Retrotechtacular: Fog Over Portland

June 1, 2016 by 23 Comments

In the early days of broadcast television, national spectrum regulators struggled to reconcile the relatively huge bandwidth required by the new medium with the limited radio spectrum that could be allocated for it. In the USA during the years immediately following World War Two there was only a 12-channel VHF allocation, which due to the constraints of avoiding interference between adjacent stations led to an insufficient number of possible transmitter sites to cover the entire country. This led the FCC in 1949 to impose a freeze on issuing licences for new transmitters, and left a significant number of American cities unable to catch their I Love Lucy or The Roy Rogers Show episodes.

The solution sought by the FCC was found by releasing a large block of UHF frequencies between 470 and 890 MHz from their wartime military allocation, and thus creating the new channels 14 to 83. An experimental UHF pilot station was set up in Bridgeport, Connecticut in 1949, and by 1952 the FCC was ready to release the freeze on new licence applications. The first American UHF station to go on air was thus KPTV in Portland, Oregon, on September 18th of that year.

UHF TV was a very new technology in 1952, and was close to the edge of what could be achieved through early 1950s consumer electronics. Though the 525-line TV standard and thus the main part of the sets were the same as their VHF counterparts, the tuner designs of the time could not deliver the performance you might expect from more recent sets. Their noise levels, sensitivity, and image rejection characteristics meant that UHF TV reception  did not live up to some of its promise, and thus a fierce battle erupted between manufacturers all keen to demonstrate the inferiority of their competitors’ products over the new medium.

The video below the break delivers a fascinating insight into this world of claim and counter-claim in 1950s consumer electronics, as Zenith, one of the major players, fires salvos into the fray to demonstrate the superiority of their products over competing models or UHF converters for VHF sets. It’s very much from the view of one manufacturer and don’t blame us if it engenders in the viewer a curious desire to run out and buy a 1950s Zenith TV set, but it’s nonetheless worth watching.

A key plank of the Zenith argument concerns their turret tuner. The turret tuner was a channel selection device that switched the set’s RF front end between banks of coils and other components each preset to a particular TV channel. Zenith’s design had a unique selling point that it could be fitted with banks of components for UHF as well as VHF channels thus removing the need for a separate UHF tuner, and furthermore this system was compatible with older Zenith sets so existing owners had no need to upgrade. Particularly of its time in the video in light of today’s electronics is the section demonstrating the clear advantages of Zenith’s germanium mixer diode over its silicon equivalent. Undeniably true in that narrow application using the components of the day, but not something you hear often.

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Can You Hear SamSat-218D?

May 5, 2016 by 44 Comments

Students of the Samara State Aerospace University are having trouble getting a signal from their satellite, SamSat-218D. They are now reaching out to the radio amateur community, inviting everybody with sufficiently sensitive UHF VHF band (144 MHz) equipment to help by listening to SamSat-218D. The satellite was entirely built by students and went into space on board of a Soyuz-2 rocket on April 26, 2016. This is their call (translated by Google):

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Weightless IoT Hardware Virtually Unavailable

December 28, 2015 by 36 Comments

It has been over 2 years since we last mentioned the Weightless SIG and their claims of an IoT open standard chip with a 10 year battery life and 10km wireless range, all at a jaw dropping price of $2 per chip. There was a planned production run of the 3rd gen chips which I would suspect went to beta testers or didn’t make it into production since we didn’t hear anything else, for years.

Recently, a company called nwave began producing dev-kits using the Weightless Technology which you can see in the banner image up top. Although the hardware exists it is a very small run and only available to members of the development team. If you happen to have been on the Weightless mailing list when the Weightless-N SDK was announced there was an offer to get a “free” development board to the first 100 development members. I use bunny ears on free because in order to become a member of the developer team you have to pay a yearly fee of £900. Don’t abrasively “pffffft” just yet, if you happened to be one first 100 there was an offer for developers that came up with a product and submitted it back for certification to get their £900 refunded to them. It’s not the best deal going, but the incentive to follow through with a product is an interesting take.

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