Restoration work on an RCA transmitter

I read through this article about the ongoing restoration work of an RCA SSB T-3 transmitter and found it interesting.  The RCA T-3 transmitter is a 20 KW SSB/ISB HF (2-28 MHz) unit designed for point-to-point telephony service.  Because SSB requires class A or AB low distortion amplifiers, this is a large unit, even for its age and power levels.

From the looks of the before pictures, this transmitter was in sorry shape.

Here is a brief video of the transmitter start-up:

These units were designed to be switched on and run at 100% duty cycle for most of their operating lives. That is some heavy iron there.  This particular unit was made in 1959. More here and video part 2:

Anyway, before geosynchronous satellites, HF point-to-point transmitters were used to make long-distance phone call connections and send data and pictures back and forth over long distances. Out in Hicksville, Long Island, Press Wireless ran a data and fax system that used HF for long-haul data transmission.  Much of the WWII reporting from Europe and the Pacific Theaters was carried over this system.

Text would be printed out on a mechanical teletype machine at something like 60 words per minute, which was considered fast for the time:

Tuning across the band, one can often hear Radio Teletype (RTTY or RATT) which uses a 5-bit Baudot code, 170 Hz shift with 2125 HZ representing a Mark or 1 bit and 2295 Hz representing a Space or 0 bit, which is a bit different from the Bell 103 modem specifications. This is what it sounds like at 75 Baud:

So slow you can almost copy that by hand.

The RCA H (SSB T-3) unit above was independent sideband (ISB), which means that either sideband or both could be modulated independently of the other, thus two channels of information could be transmitted.  SSB bandwidth is about 2.7 KHz, which is good for telephone-grade audio or low-speed data.

I sort of wish I was living in California again, I’d lend a hand.

HF broadcasting station maintenance

This video shows some of the maintenance required for an HF (AKA Shortwave) broadcast station. It starts with transmission line tensioning, some shots of a curtain array then goes on to show the inside of a transmitter building. Transmitters shown are Harris HF-100 (a 1980’s model tube type PDM design) and Continental 418, but I didn’t see the letter number. They are likely tube-modulated units.

These are from the international service of Australia Broadcasting Corporation (ABC), or Radio Australia International.

Goodbye, RCI 1945-2012

RCI logo
RCI logo

In yet another example of government-sponsored international broadcasting ending, Radio Canada International calls it quits after 67 years.  Effective June 24, all broadcasts from RCI’s Sackville shortwave relay site will cease.  All satellite distribution will end and seventy-five percent of the RCI workforce will be laid off.  This means the end of almost all RCI original content.  The good news, according to the press release, is that RCI will continue on webcasting.

This is due to budget cuts to the CBC, which administers RCI.  The Canadian Parliament cut the RCI budget from $12.3 million CAD to $2.3 million CAD for 2012.  This cut in expenditures is saving each Canadian resident approximately $0.35 CAD per year.

Thus, this weekend is the last chance to hear RCI or CBCNord Quebec on any HF frequency.

I listened to RCI for many years, until they drastically reduced their English language shortwave broadcasts to North America in 2006.  Simply put, HF broadcasters are folding up shop and moving toward web-based distribution networks.  Those HF transmitters are expensive and they do not maintain themselves.

One drawback of this scheme is government censorship.  It is very easy to the government to block access to sites via internet firewalls.  It is very difficult to completely jam a radio station.

And perhaps those considerations are not important.

RCI transmitter site, Sackville, NB
RCI transmitter site, Sackville, NB, courtesy of Wikipedia

I wonder what will happen to their transmitters after sign-off?  According to the wikipedia article there are nine HF transmitters in use, with power levels ranging from 100-300 KW.  They are likely to be hauled away and scrapped, the building torn down.

CHU: Time nor tide waits for no man

CHU is an HF time signal station operated by the National Research Council of Canada. It operates 24/7 and announces the hour and minute each minute of every day on frequencies 3,330, 7,850, and 14,670 KHz. This is the Canadian counterpart to WWV and WWVH.  In the strictest sense of the term, it is a broadcasting station, although many would also classify it as an HF utility station as well.  Many countries had HF time signal radio stations at one time, but there are fewer now.  Back in the day before GPS, these time signals were critically important to anyone needing coordinated event timing.  We used the carrier frequency from WWVH as our frequency standard for test equipment.  WWV and WWVH also transmitted a very accurate 1 kHz tone for the same purpose.   According to the CHU website:

Normally CHU’s emission times are accurate to 10-4 s, with carrier frequency accuracy of 5×10-12, compared to NRC’s primary clocks, which are usually within 10 microseconds and 1×10-13 compared to UTC.

Additionally, every minute between 31 and 39 seconds, CHU broadcasts FSK time code with a Bell 103 standard (2225 Hz mark, 2025 Hz space) at 300 bits/second (IRIG time code).  This could be used as a backup for GPS time clocks on automation systems if GPS were to fail for some reason. One would have to write a little software program to decode the hex output and reset the computer clock once per minute accordingly.  That should not be too hard.  LINUX information and software can be found here.  More on CHU time code here.

CHU Ottawa, Ontario, Canada
CHU Ottawa, Ontario, Canada

In my location 3,330 KHz is audible 24/7.  That signal is transmitted with a carrier power of 3 KW into a non-directional vertical dipole antenna as is 14,670 KHz.  The 7,850 KHz signal is transmitted with a carrier power of 10 KW into the same type of antenna.

Canadian Time Signal station CHU, aerial view
Canadian Time Signal station CHU, aerial view

There is some discussion of adding an additional time station transmitter in western Canada and of changing the modulation from AM to DRM or at least adding some type of DRM service.