The mechanical tower light flasher

This is a Hughey Phillips mechanical tower light flasher that has been in service since 1960. Basically it is a motor connected to a cam that rocks a mercury relay back and forth. These were standard technology for tower lights from the 1930’s through about 1970 or a little later.  They were very reliable, we still have some with a “pancake motor” in use on some of our towers.  They were very robust and immune to lightning damage, RF interference and other problems.  The only maintenance that I can think of is lubricating the motor bearings.  Eventually, however, they do wear out.  Cold weather seems to take its toll, often causing the motor to stop.

Hughey and Phillips mechanical tower light flasher
Hughey and Phillips mechanical tower light flashe

This particular unit is mounted inside the tuning house for the far tower (north tower) at the WGHQ antenna array.  It has finally reached the end of it’s existence; the motor bearings are shot and it has gotten stuck in both the on and off position this year causing the FAA to be notified of the malfunction.

WGHQ 920 Khz Kingston, NY antenna array
WGHQ 920 Khz Kingston, NY antenna array

Today, I am replacing it with a solid state flasher (SSAC B-KON FS155-30RF).  Solid state flasher units have been known to malfunction in high RF fields, such as AM towers.  To cure that, the manufacture has built in 0.01 uf bypass capacitors, hence the “RF” suffix.  Older units did not have the built in bypass caps, so external 0.1 uf bypass capacitors were normally installed on units mounted to AM towers.  While I was working on this, I turned the transmitter down to 500 watts, no need getting any RF burns.

Naturally, this has to happen after there is two feet of snow on the ground.  Also, it should be noted that this is the furthest tower away from the transmitter building.  Now where did I put those snow shoes?  Never mind, it has been very cold and the ground is frozen solid, I’ll take the truck…  This is good because I will have all the tools, drills, nuts and bolts without having to walk back and forth several times in the snow.

Hughey Phillips mechanical beacon flasher
Hughey Phillips mechanical beacon flasher

I removed the motor and mercury filled relay.  I’ll have to figure out how to dispose of the relay.  I then drilled a mounting hole through the base of the old flasher housing and bolted the solid state relay to it.  This is required because the solid state relay needs a pretty good heat sink.

SSAC B-KON tower light flasher
SSAC B-KON tower light flasher

Turn everything back on and:  Ta-da! All works normally, tower beacon is flashing away up there.  Time to leave.

Truck stuck in swamp
Truck stuck in swamp

Pull forward about 2 feet to turn around and CRUNCH!  The truck goes through the ice of a hidden stream.  Any attempt to move only makes it worse:

Truck rear burried to axle
Truck rear burried to axle

Put in a phone call to the one guy I know that can get me out.  About an hour later he shows up with chains, a shovel and a come-a-long.  We attach the come-a-long to the fence support post and pull the truck out backwards 1/2 inch at a time.  It took us about an hour and a half to get it all the way out so I could drive it back across the field.  I’d have taken some pictures, but my guy; he was a little grumpy.

I won’t do that again.

Still, I did the job I came to do, so it was a good day after all.

WE2XRH and the NVIS antenna

WE2XRH looks like an Amateur radio call sign but it is actually the call sign of an experimental short wave station in Alaska.  Transmitting DRM on 4.85 MHz, 7.505 MHz and 9.295 MHz with a Near Vertical Incident Skywave antenna system, they hope to cover all of Alaska and almost nowhere else with shortwave broadcast.

WE2XRH DART coverage with NVIS antenna system
WE2XRH DART coverage with NVIS antenna system

This license was granted for two years in August of 2008 and renewed again this September until  July 2012.  According to the website Nextgov.com:

The company told FCC that its initial tests would be funded by and conducted for the Defense’s Joint Electromagnetic Technologies program, a classified operation whose mission is to develop technologies for use by special forces and intelligence units.

Defense also will supply surplus transmitters from the closed, Cold War-era Over the Horizon Radar, located in Delta Junction. The radar system bounced shortwave signals off the ionosphere to detect aerial targets, such as Soviet bombers, at ranges up to 1,800 miles.

The transmitters are 100 KW Continental HF units, which for this applications are running about 20 KW.  According to this Yahoo Groups posting, several Japanese shortwave DXers have received the station in late 2009, but nothing recently.  I shot an e-mail off to their information address, but did not receive a reply.

On High Frequency (HF) NVIS has been used for several years where line of sight VHF communications are not possible.  Soldiers during the Vietnam war noticed that if a vertical whip was bent over so that it was horizontal to the ground, the signal strength was slightly less but the signals were much less prone to fading.

Near Vertical Incident Skywave antenna angle vs. distance
Near Vertical Incident Skywave antenna angle vs. distance

In this case, WE2XRH is using a crossed dipole antenna which generates a circularly polarized field.  With traditional HF skywave, polarization is not a factor since the ionosphere usually causes some field rotation anyway.  It is interesting that the system had this design consideration.

The NVIS is a novel approach and it may work on Medium Frequency (MF) during the night time, but daytime coverage would still have to rely on ground wave signal.  The FCC has historically approached MF skywave as a secondary and unreliable transmission method.  The idea being to reduce the antenna take off angle to as low as possible, hence the popularity of taller than 90 degree towers.  There is good validity to that practice as mixing the ground wave and skywave components at a receive antenna will cause multipath fading.

Setting aside a new broadcasting frequency segment, say 1.6 – 1.8 Mhz, a system could be designed to transmit DRM by using groundwave during the day with a traditional 90 degree tower, and NVIS at night with a horizontal dipole antenna.    Then never the two should meet.  The night time NVIS system would have a small ground wave component, out to a couple of miles.  In addition to that, the night time NVIS system can run on an adaptive power system, when propagation conditions are poor, more power can be applied to the antenna input and in better conditions, power reduced in accordance with a remote receive monitor that reports the Bit Error Rate (BER) back to the transmitter controller.

The best NVIS antenna is the 1/2 wave dipole positioned between 0.1 and 0.2 wave lengths above ground. In the 1.6  to 1.8 MHz band, that equates a half wave dipole antenna 260 to 292 feet long mounted between 66 to 90 feet above ground level.

This would have many advantages over the current directional antenna based MF broadcasting system currently deployed.  The current system is based on pushing potential harmful signals away from a station that was licensed to the same frequency (or an adjacent frequency) earlier.  This puts the onus for proper operation on the broadcast license holder.  Most don’t have the know how or resources to insure that a n AM directional is operating properly.  I would estimate at least half of the directional AM antennas in this country are out of tolerance.  With a NVIS based night time antenna system, coverage areas would be assigned much like an FM allotment.

The BBC conducted medium wave DRM tests in 2007 with satisfactory results during the daytime, but poor reception at night time due to co channel interference.  That is why DRM will not work on the current AM broadcast band and if digital radio is to be broadcast on MF, a new frequency band would be needed.

The Devil is in the details

Sometimes it is the seemly small insignificant detail that will take a station off the air. To expound on that a bit, I have my own story which happened yesterday.  The back story is this:  About three years ago, some unauthorized tower climbers climbed the WICC south tower all the way to the top.  The station remained on the air at full power while this was going on.  Once at the top of the three hundred foot tower, the climber, we can call him “Crack Head,” manged to loosen, then remove the beacon and throw it to the ground.  Mind you, this guy had no safely climbing equipment whatsoever and he had to stand on the top plate, which is all of 20″ x 20″ square, of which the beacon takes up 16 inches.  A two inch purchase between himself and eternity demonstrates that God does indeed smile on fools and drunks.

WICC south tower with long island sound in background
WICC South tower with Long Island sound in background

Fortunately, his friend on the ground had a video camera and filmed the entire episode.  Even better, they then posted it on Youtube.   The police took interest in this video and it’s owners because the damage to the radio station was significant, and with the tower being about a mile away from the end of the Stratford Airport runway 17, presented a real hazard to air navigation.  Needless to say, the video was used by the prosecution and both crack heads are now in prison, God having limits after all.

A spare beacon was hoisted to the top of the tower an placed in service.  This beacon was quite old and leaky and continually failed, burning out the tower light flasher.  Thus, it was time to replace it.  We took advantage of the outstanding weather and the crew from Northeast Towers made quick work of it.  Removing and lower the old beacon to the ground, then hoisting the new beacon up and installing it.  I goobered it by not taking pictures of the beacon fixtures flying up and down the tower.  I took the station off the air for about five minutes to check the condition of the wiring going up the tower, making sure there were no shorts up the tower or back toward the transmitter building.  While I was doing this, I overheard the two way radio conversation between the tower climber and the ground crew on wiring.  It seems the old beacon had only two wires, hot and neutral.  The new beacon had three wires, hot, neutral and ground.  Tie the neutral and ground wires together, instructed the tower boss.

Nothing more was though of that, it sounded okay to me.  Unfortunately, the tower had other ideas.  About an hour after we secured from the job and drove away, the station went off the air.  It seems the neutral wire was not referenced to the tower previously.  Because now the neutral wire was tied to the top of the tower, the RF found a path to ground via the tower lighting choke at the base of the tower.  It started arcing to it’s access door causing the transmitter to go off around 4 PM.  Equally unfortunate was the fact that the construction gate was closed and I had to get a boat ride with the harbor master, which took about an hour to arrange.  The entire situation was further complicated by darkness, which comes predictably around 6:30 PM this time of year.

When I arrived back out at the base of the tower, I took the metal access door off of the tower light choke cabinet.  I could see the fresh track marks all across the bottom of the door. With the door off, I turned the transmitter on.  Worked just fine.    I tried cleaning it off with a Scotch Bright, but to no avail, the transmitter would not run at any power level with the door in place.

Finally, the harbor master becoming impatient and darkness quickly falling, I taped a garbage bag over the tower light choke box with the door off and turned the transmitter back on.  The tower crew will have to come back and remove the ground wire on the beacon.

The first rule of trouble shooting: Check the last thing that was worked on first.

Update:  And look, here is the original story in Radio World: Tough times a Pleasure Beach.

The folded Unipole antenna

In the 1990’s, the folded unipole antenna was touted by many to be the savior of AM radio.  There were many claims that a folded unipole antenna did not need a complicated ground system, a simple ground rod at the base of the tower would work fine.  That turned out to be not exactly the case.   Kintronic did a study (.pdf) that basically dispelled that notion, along with several others.   The folded unipole antenna performed within a few percentage points of a series fed tower under the same testing conditions.

three wire folded unipole on a guyed tower
three wire folded unipole on a guyed tower

Folded unipoles do have the advantage of a grounded tower.  Grounded towers have a distinct advantage in lightning prone areas, such as central Florida.  I can attest through my own experience, a series fed tower is much more likely to induce lightning damage to a transmitter or ATU.  Folded unipole tower systems can also be used to co-locate other antennas, such as STL, cellular, PCS, etc.  Making some extra rental money on an AM tower is not a bad way to go.

I began fooling around with MANNA-GAL, which is a NEC-2 based program.  It is a free ham radio program, so it is a little clunky to use and it took a while to figure out, but once I did, it is fun.  I modeled a unipole antenna for medium wave use and the results are pretty interesting.  First of all, I drew out X-Y part of the system on graph paper because the program requires all wires (elements) be entered in a coordinate based format.  The Z axis is the tower, since there is only one of those, that was easy.  I played around with series vs. unipole systems and the results were fairly close to what they are supposed to be.  One of the nice things about MANNA-GAL is it allows the user to change the ground conditions.  To add a unipole to the tower, I put 3 wires spaced between one to two meters away from the primary Z axis wire, connected them to the top of the tower and changed the drive point to the skirt wires.

The interesting part is when I added an above ground counterpoise instead of a buried radial ground system.  I think Ron Nott, of Nott, ltd. did much of this work too.  What I found was that with between 5 – 10 above ground radials of 90 degrees or greater, the efficiencies are within about 10 percent of theoretical for a 120 buried radial system.  Again, the ground conductivity plays a big roll in this, poor ground conductivity will reduce efficiencies equally for both systems.

As the tower height approaches 110 degrees or so, depending on the spacing from the tower of the skirt wires, the bandwidth really starts to open up.  At 110 degrees the base impedance is about 120 ohms with about 80 ohms inductive reactance.   Both the impedance and reactance slope slightly upward with frequency but are linear +/- 50 KHz of carrier.  This slight asymmetrical sideband distribution can be easily canceled out in the ATU with a few degrees of negative phase shift through the T network.

Again, all of this is theoretical, but I have found that NEC is usually within +/- 10% of real world values.  It is difficult to get a handle on ground conductivity unless measurements are taken.  Even from season to season, that can change.

The above ground counterpoise requires a partial proof, according to FCC 73.186.  If this were a directional station, this would be required anyway.  For a non-directional station, it is pretty easy, for six radials, it would probably take about one to two days of driving around with a FIM 41.  The other consideration is public exposure to RFR from the radials.  This can easily be measured with a NARDA meter.  More radials will spread the induced currents out more, for for higher powered stations, 10 above ground radials might be required.

There are several radio stations in the country which are successfully using above ground counterpoises.  It seems to be a good system and requires much less material and labor to install than the traditional ground system.

Therefore, if I were designing a new AM station, I’d use a grounded tower between 105 and 110 degrees with a unipole and 6 above ground radials 90 degrees or greater.