The malfunctioning STL antenna

Right after Tropical Storm Irene, it was noted that the STL signal strength at the WHUD transmitter site was low. Normally it was 300+ µV, now reading around 100 µV, which is a problem. Upon further investigation, it was revealed that the STL transmitter on the intermediate hop had higher than normal reflected power.

Time to call the tower crew.

The STL transmit antenna for WHUD’s STL (WPOU464) hop is a Scala Paraflector (PR-950), mounted at the 280 foot level on this tower:

Scala PR-950 on a guyed tower
Scala PR-950 on a guyed tower

The fact that it happened after a major storm and the transmitter was showing higher than normal reflected power indicates a problem with either the antenna or the jumper between the 7/8″ Cablewave coax and the N connector on the antenna.  A measurement with a spectrum analyzer shows very high return loss:

WHUD STL antenna return loss
WHUD STL antenna return loss

This shows distance to fault 413 feet, with a return loss of -7.4 dB.  That distance is either near or at the antenna and -7.4 dB indicates a lot of reflected power.  We had the tower climber take apart the jumper connections and terminate the jumper with a known good 50 ohm load.  The return loss did not change.  We then had him swap out jumpers and reconnect to the antenna.  That did the trick:

WHUD STL antenna with new jumper
WHUD STL antenna with new jumper

Much better, most of the power is now being radiated by the antenna, the VSWR is 1.02:1.  The impedance bump at 51 feet is a sharp bend in the coax where it is attached to an ice bridge.  Reconnecting the transmission line to the transmitter and turning it on confirms that all is normal again.  The problem with the jumper was found in one of the connectors, it was full of water.

Water contaminated Andrew flexwell connector
Water contaminated Andrew flexwell connector

I cut away the boot, water had entered the connector from the back because waterproofing and tape was not applied all the way to the coax.  This was installed in 1998 when the station moved from Peekskill to their current location in the town of Fishkill.  The fact that it happened now in the nice weather when Mt. Beacon is still accessible and not in the middle of winter means the radio gods are smiling on us.

Donating old equipment

There is a propensity among radio engineers to save old equipment. Sometimes I look at something and think, “Man, that cost a lot of money ten or twenty years ago.”  Truth be told, much of what is saved will never be used again.  This equipment should be scraped or donated to someone who might find it useful.  One thing that is most appreciated by Amateur Radio (AKA Ham) operators are old 1 KW tube type AM transmitters.  Ham operators love these things, and with good reason.

A fair amount of repair work, some cleaning and a bit of reworking will turn what might have been a useless dust collector into a 160 or 80 meter AM rig and with a good story to boot.

Personally, I’d rather see a Gates BC1T or RCA BTA1R off to a new home than off to the scrap yard.  To that end, today we unloaded the BC1T at WLNA to a willing ham.  This particular transmitter had last run in 2001 or so and was used as a spare parts supply for other BC1T transmitters owned by the same company.  There was no way it would ever work again and truth be told, it really wasn’t needed any longer anyway.  Since the Harris MW5B was replaced as the main transmitter by a BE AM6A, the backup transmitter was never used.

Gates BC1T transmitter
Gates BC1T transmitter

John Aegerter, a frequent commenter on this blog, drove all the way from Madison, Wisconsin to pick it up.  Prior to pick up, I removed all of the tubes, transformers, crystals and glass envelope time delay relays.  I packed up the glass objects in a box.

Gates BC1T tubes, transformers and spares
Gates BC1T tubes, transformers and spares

There were several spare tubes and parts which are no longer needed.  These went with the rig, along with what ever manuals I could find.

Gates BC1T loaded into pickup truck
Gates BC1T loaded into pickup truck

The transmitter was then loaded into the back of a Dodge Ram 2500 pickup truck and tarped for it’s trip back to Wisconsin.

Newest Radio Thing

Just in time for the NAB, I’ve been working on this design since my college days. To give you some idea of how long that is, I am nearly 47 years old. I believe it has finally been perfected, now I just need to find somebody to make it. I guess I could send it off to China and get circuit boards made, but they would steal the design.

From the website xkcd.com, which has, perhaps the best website ever published in the history of the internet, here.

Oh yeah, and April Fools!

Radiation levels: Compare and Contrast

Not related to radio engineering, however, I’ve been doing daily radiation measurements at my house (upstate NY) since the Fukushima disaster. A few bits of house keeping information first: This is a CD V-700 radiation meter, which is a model 6 manufactured by Anton. It was last calibrated in 1986. When I place the Geiger tube over the operational check source, it goes up to about 2 mr/hr as described in the owner’s manual. It may not be completely accurate, but it is accurate enough for this experiment.

This video was taken on March 17, 2011. It sets a good reference for normal background radiation levels:

This video was taken on March 27, 2011. It shows a significant increase in background radiation. Further, much of this appears to be gamma radiation, as the gamma shield is closed during this video:

Both of these videos were taken on the most sensitive (x1) setting. It shows that the radiation level is about 8 to 10 times above normal. It is a cause for concern, but not alarm. Not yet. If it continues at this level for several days or weeks, then the overall radiation exposure will begin to accumulate. Right now, it is about the same as taking two NY to Los Angles flights per day, according to this chart (0.35 mr/hr = 3.5 uSv per hour x 24 hours = 84 uSv per day):

Radiation chart
Radiation Chart

As of March 28, 2011, the wind has shifted more to the south west and the levels have dropped somewhat. From our beloved press corps, there have been a few reports here or there on this, most with the standard “this is nothing to worry about” disclaimer. I have also noticed a series of stories and reports that radiation is not all that bad, don’t worry about it, living next to a nuclear plant is fun(!), and we don’t know as much about radiation as we thought we did. I don’t know about all that, I’d rather base my opinion on the scientific body of evidence gathered over the last one hundred years or so. The conclusion of that information is that radiation is bad for human physiology and exposure should be limited.

There is also a crowd source website called “Radiation network,” which is showing all the levels across the US are normal. This makes me wonder about their instruments and or candor, you can draw your own conclusions.