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This information is from an occasional reader who wished to remain anonymous.

Another AM station surrenders its license, this time from north of the border. CKSL, London, Ontario, Canada is gone for good.  Current owner, Bell Media, has determined that it would cost more to repair the deficiencies with the antenna system than economically feasible, especially considering it’s low ratings.  Here is their filing with the CRTC:

Bell Media is the licensee of CKSL-AM 1410, assuming stewardship of the station in 2013 as part of the Astral Media acquisition.

A technical review of the transmitter site was recently completed both by Bell Media and contractors, which has resulted in the determination that the AM array poses an unacceptable risk from a health and safety perspective.  The five towers are experiencing serious structural degradation and also require repairs to the aviation safety lighting system. In addition, the building which houses the transmitter has shifted off its foundation (as have several of the individual tower sheds).

Given these problems, Bell Media would need to make a significant financial investment to bring CKSL-AM’s transmitter up to compliance with Human Resources Development Canada, Industry Canada and NavCanada operational codes and standards, all of which is estimated to exceed $3 million dollars.

From a market perspective, CKSL-AM has consistently ranked last out of all ten commercial stations in the London market, both in audience share and revenue generation, over the last several years.  In fact, since 2013 the London market has seen radio revenues drop 4% and CKSL-AM generates the least amount of revenue of the stations in the market. Even with a significant investment in programming, this trend is unlikely to be reversed. 

In light of the significant capital costs coupled with the absence of revenue and audience share, Bell Media is respectfully requesting the revocation of the CKSL licence.

Well, 24/7 comedy will do that to you.  Somebody in the business said to me recently “The listeners are abandoning radio!”  No, it is the broadcast station owners who are abandoning their listeners and their cities of license.  I have a news flash for all current broadcast station owners; as surprising and radical as this might sound, bland, boring, canned, completely irrelevant, dismal, uninformative, unimaginative, unentertaining, dreary, stale, unenjoyable programming will drive away even the most loyal listeners.  People really want to listen to radio, it is an easy habit and readily accessible.  Radios are ubiquitous; they are in our kitchens, bedrooms, cars, hotel rooms, offices, restaurants, barber shops, etc.  That, however, may not always be the case, as more and more people move Spotify, Pandora, or Apple radio when they are tired of the disappointment.  I was listening to a certain sports radio format the other day and I kept waiting for something interesting to happen.  I waited and waited. I would say to myself; okay, this will be the segment when I will learn something or be entertained.  This upcoming guest will say something interesting.  Sadly, those expectations were never met and I will never tune into that station again. Elevator music would have been better.  Worse than sports radio, 24/7 comedy is the absolute death knell.  This is like saying; we are out of ideas and we do not care.

Here are a few pictures of the former CKSL-AM transmitter site:

CKSL antenna array
CKSL antenna array
CKSL_transmitter
CKSL transmitter building
CKSL_transmission
CKSL transmission line bridge
CKSL_tower
CKSL tower base

Actually does not look too bad, at least the field is mowed. I have seen much, much worse.  Those bolt together towers, though. I would bet that they are the real problem, bolts are deteriorating faster than the tower steel. Very likely all the towers need to be replaced and that is why the license is being surrendered.

If you are a radio geek, get out there and take some pictures of your favorite radio station.  If the current trends continue, eventually they will all be gone.

The Horns of a Dilemma

Alternate title: Building and ATU in a truck body tool box.

Alternate title II: I should get paid extra for this shit.

There is an AM radio station that is near death but the owners do not want it to go away.  Nor to they want to spend very much money to keep it around, thus the dilemma.  At the transmitter site, there are a multitude of problems; leaking roof, very old rusty ATU, rotting support posts and transmission line bridge, equipment racks rusting out, nothing is grounded properly, the building is full of junk, snakes and mice have moved in.  To further complicate things, the tower and transmitter building serve as an STL relay point for two of the market’s FM stations.  There is also two translators with antennas on the tower.  The ATU and tower light choke box are rusting through, which is causing arcing and broadband RF noise that is interfering with the FM station’s STL receiver.  There was a home made isocoupler for one of the translators that was allowing AM RF back into the building which was creating havoc with everything.  Because of this, the AM station is currently silent.  In short, it is a mess.

WCHN ATU
WCHN ATU

The red box on the bottom is the ATU, the plywood box on the top with the peeling yellow paint is the home made isocoupler, the tower light choke box is behind the isocoupler.

Crumbling old ATU output capacitor in series with tower
Crumbling old ATU output capacitor in series with tower

This was the capacitor that was feeding the antenna, .0041uf, 10KV 8 amps.

We started remediation on this last February, which is not optimum time for replacing rotting wooden posts.  However, we were able to clean out the building.  The leaking roof has been repaired.  I was able to find a few old racks from a Schafer Automation system to replace the rusted out original racks.  I began the process of grounding the equipment racks, the incoming transmission lines for the STL, etc.

Cool morning, Garter Snakes warming themselves on top of a Moseley DSP-6000
Cool morning, Garter Snakes warming themselves on top of a Moseley DSP-6000
Garter Snake
Garter Snake

We will have to find out how they are getting in, the plug up those holes.

Then there was the ATU and tower light choke enclosures.  Original to the 1952 sign on, they were past their serviceable days.  Since this is all being done on a budget and nobody wants to spend money on an AM station that has little or no listeners and even less revenue, we had a problem.

Then somebody suggested building an ATU in a truck body tool box.  Well…  This isn’t the Meadowlands, so if there are no other alternatives then okay, I guess.  Off to Amazon to order a tool box.  This particular unit seems fine, my only comment is on the gauge aluminum (or aluminium if you prefer), which is slightly thin for holding up all those parts.

ATU built in a truck body tool box
Fabrication shop, ATU built in a truck body tool box

Still, the box itself is nice enough and certainly better than the old one.  I was able to reuse the inductor and the Delta current meter but the old Sangamo capacitors crumbled in my hands when I removed them.  I also saved the feed through bowls, J-plugs and other parts.  I used some copper strap to run a good RF ground from the input to the ground connection.  Overall, I am pretty pleased with the finished product.  It is a little bit tight in there, but this station only runs 1 KW, so it should be fine.

Replacement ATU mounted
Replacement ATU mounted

So, new pressure treated posts installed, the box was mounted and the transmission line connected.

Replacement ATU under power.
Replacement ATU under power.
Reused Schaffer Automation racks, much better than the 1950's Gates racks
Reused Schafer Automation racks, much better than the 1950’s Gates racks

The reused racks are old, but serviceable and a big improvement over the old, rusting out racks.  I was able to bond each rack to the ground strap that used to connect to the RCA BTA-1 transmitter.  There is one more rack to install to the right of these two.  That should give us more than enough rack space for this site.

The station is back on at full power and not interfering with the FM STLs or the translators.  You can actually touch the rack and not get an RF burn!

We are also working on an air conditioner.

Other work at this site; cleaning out the building, replacing the tower light photocell, installing a ground buss bar, some STL lightning protectors, dress the transmission lines, etc.  It is a work in progress.

 

Medium Frequency ATU design

This is a topic I have covered before, but it is worth doing it again for future reference.  The previous post covered downgrading an AM transmission facilities for WGHQ, Kingston, NY.

This is part II of that process.

WGHQ transmitter site, towers 1 and 2 removed
WGHQ transmitter site, towers 1 and 2 removed

The old towers have been cut up and put in a scrap metal dumpster. They are off to China to be melted down and made into a submarine or a missile or a tank or something useful like that.

Towers scrapped
Towers scrapped

The directional array had a three towers in a straight line with a common point impedance of 60 Ohms.  Dropping two towers greatly changed the electrical characteristics of the remaining tower, therefore the existing ATU needed a bit of reworking to match the 50 Ohm transmitter output.

First step, correct a few deficiencies left over from the old array.

Vise grip tower feed
Vise grip tower feed

This vise grip RF connection has to go. The problem is where the tower erectors attempted to solder the copper tubing.  That tower base plate is pretty big and I would wager they didn’t use enough heat to make the solder connection.  They were probably working in the winter time, thus the “temporary” fix.  This tower was put up in 1993, so that temporary fix lasted 23 years.

I removed the offending tool and soldered the connection to another part of the tower with silver solder.  The smaller cross bar made a good connection point.

RF feed correctly connected to the tower
RF feed correctly connected to the tower

After soldering, I cleaned up and sprayed some grey primer on it to prevent rust forming where I scraped the paint off.

Next, I made an impedance measurement:

WGHQ tower base impedance measurement
WGHQ 920 KHz tower base impedance measurement

That junk on the upper part of the graph is coming from WHVW on 950 KHz. The tower itself looks pretty good, 77.6 Ohms resistance with 130 Ohms inductive reactance.  Since this is not a part of a directional antenna system, the ATU design is pretty straight forward.  Given that WHVW on 950 KHz is located 10.41 miles away, a low pass filter design is optimum.  A basic low pass filter T network has inductive input and output legs with a capacitive shunt leg to ground.

T network diagram
T network diagram

Each leg is used to match the 50 Ohm transmission line impedance (R1) to the 77.6 Ohm tower impedance (R2) and cancel out the 130 Ohms of inductive reactance.  This is a vector impedance problem, much like a vector force problem in physics.   Some basic arithmetic is required (always include the units):

X1, X2, X3 = √(Zin x Zout)

X1, X2, X3 = √(50Ω x 77.6Ω) or X = 62.28Ω

The value of inductance or capacitance for each leg is calculated using the basic inductance or capacitance formulas:

L (μH) = XL / 2πf(MHz)

And

C (μF) = 1 / 2πf(MHz) XC

Thus the input leg, or X1 = 62.28Ω / (6.28 x 0.92 MHz) or 10.78 μH

The Shunt leg, or X2 = 1 / (6.28 x 0.92 MHz x 62.28Ω) or .0028 μF

The output leg is a little different.  The tower has 130 Ohms of inductive reactance that needs to be cancelled out with a capacitor.  Rather than cancel out all of the inductive reactance, then add an inductive output leg, the tower reactance can be used as part of the tuning circuit.  The design calls for 62.28 Ohms inductive reactance, so 130Ω – 62.28Ω = 67.27Ω, which is the value needed to be cancelled by a capacitor:

Output leg, or X3 = 1 / (6.28 x 0.92 MHz x 67.27Ω) or .0025 μF

A little Ohm’s law is used to calculate the base current for both the day and night time operations.

Ohm's law pie chart calculator
Ohm’s law pie chart calculator

Thus the daytime base current is I = √(P/R) or I = √(1000 W/77.6Ω) or 3.58 Amps.

Night time base current is I = √(38 W/77.6Ω) or 0.70 Amps

Current handling requirements:

Base current is calculated to be 3.6 Amps at 1,000 Watts carrier power.  Allowing for 125% peak positive modulation makes it 5.7 Amps.  Having safety factor of two or 11.4 Amps output leg and 14 Amps input leg.

Voltages: 353 maximum input voltage, 439 output.

Thus, 20 amp, 10 KV parts should work well.

The designed schematic for the ATU:

WGHQ ATU Schematic diagram
WGHQ ATU Schematic diagram

Putting it all together.

Since the tower looks fairly broad at 920 KHz, we are going to attempt a nice broadband ATU to match it.  This station is currently programmed with a classic country format, and I have to tell you; those old Conway Twitty, Merle Haggard, Patsy Cline, et al., songs sound pretty good on the old AM radio.  The Subaru stock radio has HD, which also has a nice broad IF section, thus allowing all those lovely mid-high range frequencies through.

This is the existing ATU, which I believe was built by Collins in 1960:

WGHQ Tower 3 ATU
Existing WGHQ T network ATU

The ATU building is a little rough, but the ATU itself is in remarkable shape for being 56 years old.  The input leg inductor is in the center and will be reused as is. The large Jennings vacuum capacitor at the bottom is a part of the shut leg.  Its value is 2000 pF at 15 KV.  The top vacuum capacitor is series output cap, its value is 1000 pF at 15 KV.  The basic plan is to move the upper cap down in parallel with the bottom cap.  The shut leg inductor will be kept in place to tune out any access capacity.  For the output leg, I have a 2500 pF mica cap and a 10-100 pF variable cap connected in parallel.  The inductor on the output leg will be removed.

After some re-work on the ATU components, I tuned everything up.  The easiest way to do this is to disconnect the legs, measure them individually and adjust them for the desired reactance, which in this case is 62.28 ohms or thereabouts.  The output leg was measured with the tower connected since the tower reactance is a part of the tuning circuit.  The input leg was right about 10 μH.  The shunt leg turned out to be about 0.002 μF.  This is often the case, theoretical values are slightly different than field values due to stray capacitance and inductance in the connecting straps, etc.

This is the load, as measured at the output terminals on the transmitter:

WGHQ tower load as measured at the transmitter output terminals
WGHQ tower load as measured at the transmitter output terminals

Slightly asymmetric on 910 KHz, but overall pretty good. There is a fair amount of phase rotation in the transmission line due to the length from transmitter to tower (855 feet, 260.6 meter), which works out to be 0.93 wave length allowing for the 86% velocity factor of the transmission line.

Time to pack up and go home.

Downgrading an AM radio station

WGHQ in Kingston, NY has been downgraded from a 5KW DA-1 to a 1KW non-DA system.  This was done because two of the three towers in the directional antenna array dated from 1960, were in very rough condition and needed to be replaced.  The remaining tower (furthest from the transmitter building) had been replaced in 1994, is in good condition and is being kept as the non-directional radiator.

Here are a few pictures:

WGHQ 3 tower directional antenna array, Port Ewen, NY
WGHQ 3 tower directional antenna array, Port Ewen, NY
More deferred maintenance
More deferred maintenance
RF and tower light feed disconnected from tower base
RF and tower light feed disconnected from tower base
Second tower base vegetation not as bad, tower disconnected
Second tower base vegetation not as bad, tower disconnected
WGHQ transmitter and original Collins phasing cabinet
WGHQ transmitter and original Collins phasing cabinet

First tower video (sorry, I appear to have no idea what I am doing with the camera):

Second tower video, this one is better:

Towers on the ground:

I made measurements on the third tower and constructed a temporary ATU with parts on hand to get the station back on the air. They are now running 1 KW day, 38 watts night, as per their CP. I will be going back up to finish the job once the brush has been removed from around the existing tower and the ATU building has been repaired.  The coverage with 1 KW is not bad, actually:

Predicted coverage map from FCC website
Predicted coverage map from FCC website

The translator is on its way.