Family Radio’s WYFR shortwave service will be ending on June 30, 2013.
Shortwave transmitting is very expensive, and no doubt, competing IP distribution technology and diminishing returns on such investment must play a factor in this decision. Family radio has been struggling ever since the world did not end as predicted in 2011.
I found this video called Empire of Noise about broadcast radio jamming. It seems to be about ten years old and is a post cold war documentary about the jamming of radio signals by the USSR, Warsaw Pact counties and China. It is an interesting look into the extent and expense that governments will go to to suppress counter thought and ideas.
The video is quite long, and there are stretches of jamming noise that can be annoying, but perhaps that is the point. It is worth the time if interested in history and radio broadcasting. You know what they say about history; those that do not understand history are destined to repeat it.
A few of the highlights:
The former Soviet Union had the most extensive jamming network of anyone on Earth. There were groundwave jamming centers in eighty one Soviet cities which consisted of approximately 10-15 transmitters each in the 5 KW covering the medium and shortwave frequencies.
Each groundwave jamming station consisted of a transmitter site and a receiver/control site. The receiver site possessed lists of frequencies to monitor, when objectionable material was heard, the jamming transmitters were turned on.
There was a skywave jamming network consisting of 13 jamming stations with 10 or more 100-200 KW transmitter in each. There were some transmitters in the 1,000 KW power range. These were located in Krasnodar, Lvov, Nikolaev, Yerevan, Alma-Ata, Grigoriopol, Sovieck, Novosibrisk, Tashkent, Khanbarovsk, Servdlosk and Moscow (some of these names may have changed). These operated in a similar fashion to the groundwave jammers.
After sign off of government stations, Soviet jammers sent a blanketing signal on the IF frequency (most likely 455 KHz) of receivers to effectively block them from receiving any station while USSR government stations were off the air.
Baltic states had 11 jamming stations with approximately 140 transmitters
Ukraine had approximately 300 Jamming transmitter.
Warsaw Pact countries had extensive medium frequency jamming networks.
It is estimated it takes about 20 times the transmitted power to jam any one signal.
The entire jamming network was hugely expensive to equip and operate, costing several tens of millions of dollars per year.
It is interesting that the US position in all of this was:
Everyone has the right to seek, receive and impart information through any media and regardless of frontiers. Jamming of radio broadcasts is condemned as the denial of the right of persons to be fully informed concerning news, opinions and ideas.
Sounds perfectly reasonable. The free exchange of ideas and information over the internet is something that should be guarded carefully and should not be restricted or censored. Perhaps somebody should inform congress.
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 transmitter start up:
These units were designed to be switched on and run at 100% duty cycle from 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 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 side band (ISB), which means that either side band 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.