Scott Fybush said:
This is the infamous Cuban wobbler. It's been a topic of discussion on the various DX club lists for years now:
http://curt.deegan.com/WWWR/wobbler/wobbler5.html
Scott,
I read the discussion on the link, and have some issues with the data behind the conclusions.
There is mention that Cuba is jamming everything in Spanish in FL and PR. This makes no sense. First, in PR Cuban signals, some of which are quite powerful, are not easy catches. There is just not a good E-W propagation path inside the tropics there. Then, most of the PR stations with any power are directional away from Cuba. The rest are such low power that they could not be heard in Cuba, even without the much more powerful Colombians and Venezuelans on the same channels. Finally, many of the bold red channels have no station in PR at all and no Spanish language one in FL, either.
To me, that eliminates the idea that the wobblers are jamming specific broadcasts. If Cuba does not even try anymore to block Miami's 50 kw WQBA-1140, they certainly won't jam some music station programming to Puerto Ricans in Orlando or Tampa.
That leaves us with the power grid concept. I find that to be an odd idea with one exception. I've lived in and run and managed (and engineered) stations throughout Latin America. Even in Puerto Rico, we all had generators and they would typically run 200 to 400 hours a year... time when the grid failed. It was worse in other places, like Ecuador, too. Yet with inadequate of fragile infrastructures, I never heard the sound of today's warblers. And I've been in, working, 17 of the countries of Latin America.
What is my exception? The one unique thing in Cuba is that most of the transmitters, particularly 10 kw and over, are Czech and from the 60's and 70's. They are conventional high level plate modulated (the Czechs tried to sell me some in 1967 in Quito) and are neither a good nor a bad design. What they all had in common was the use of Svetlana tubes. Some Svets were direct copies of Eimac and Phillips power tubes. Others were unique to the Russian tube manufacturer, and most have been discontinued. The Cuban transmitters have been field modified for other tubes, and, although this is not a hugely challenging process, there may be some quality of those transmitters that creates images, spurs or whatever when the transmitter is modified. It's really unlikely that the folks who designed the transmitters are available to consult, either.
What I am familiar with, having for a while maintained one, is the RCA Ampliphase of the 60's. This AM transmitter sounded great... for several days after tuning. From there it went to hell. It generally increased bandwidth and put a lot of noise into the sidebands when out of adjustment. Thinking along those lines, perhaps the Cubans came up with some other transmitter modifications which have created this kind of situation... given the reports and the DF activities both day and night, this is rather certainly Cuba.
Going back to the late 50's and early 60's, many stations in Latin America were what we called "drifters" which wandered around close to the allocated frequency but not on it. Many Colombians would be one or two kHz above or below the licenced channel, and were nice DX catches. The cause was one of two things: Crystals ground in Colombia using poor frequency references or stations that did not have crystals and used a tuned stage, only slightly better than a ham VFO. This tuned stage operation was heat and component sensitive, so those stations had different frequencies over time. But none wandered back and forth in very precise patterns. And none produced noises on the air, either on the fundamental, a harmonic or a spur, like what we are hearing (my reference is recordings, of course).
Two of the first frequencies mentioned, 930 and 620, contain no stations that Cuba would have any interest in jamming, whether they be in the US, Puerto Rico, or anywhere around the Caribbean Basin. They certainly would not jam Venezuela today, and there is nothing able to produce a consistent signal across Cuba elsewhere.
It's hard to argue that these are jammers or sources of intentional interference. It is also hard to think that the effect comes from the power grid... which is nowhere near the worst power system in Latin America now or in the past.
Unless the Czech transmitters have some idiosyncrasy that has been created by modifications, or by additional home-brew design changes, then this is a real mystery. I favor the extreme modifications as the source.
