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An Ultimate DIY Project

How we ended up designing and building our own diplexer

AM is dead! We should stop wasting time on it and focus on FM.

I’ve heard that sentiment in various forms for years, probably going back to the late 1980s. Is it true? In some cases, yes. Is it universally true? Absolutely not!

Just take a look at the list of top stations in the big markets and you’ll likely find at least one AM in each. 

Without trying to start or extend a debate, it’s all about content. Give people what they want and they will listen. Or they would if they had receivers that could pick up those AM stations clearly … but that’s another topic for another day.

My point is, while I recognize that many AM stations are living on borrowed time, many others are alive and well and serving their markets. 

We are blessed to have a second home in the mountains a few hours west of Denver, on the other side of the Divide. Denver broadcast signals don’t penetrate that 12,000+ foot wall of granite, which means that local radio stations in the mountain communities must fill the void. 

In the town a dozen miles or so from our mountain home, a 5 kW mid-band daytimer does that very well, providing the only wide-area radio service in the region. That station has an FM translator, but because of that whole line-of-sight thing and the aforementioned walls of granite, that coverage is local to the town. But the AM goes over the hills and into the valleys and serves the whole area.

That same kind of scenario plays out in small communities all across this land. AM stations with or without translators provide service that would otherwise be unavailable. People listen because it’s the only place to get local news and weather. 

They may listen to SiriusXM, Spotify or some other service a good bit of the time, but you won’t get local news, weather and information there. You need a local broadcast station for that.

What about in the big cities? Oh sure, you’ve got KFI in Los Angeles, WINS, WOR and WCBS in New York, WGN and WLS in Chicago plus a host of others. In my hometown of Denver, KOA has been a longtime leader. But what about others in those markets? Are those stations viable? Should they be shut off and bid a fond adieu?

Based on my own experience, primarily with my employer, I can tell you with confidence that many of what some would consider “also-ran” AM stations in the large and medium markets are doing just fine. 

Sure, some have FM translators, but many don’t, or their FM signals have limited coverage because of interference and spacing restrictions. So my conclusion is that some — a lot of — AM stations are not only worth keeping but are worthy of investment.

At some point, all-digital may become a factor in that. I have mixed feelings about digital AM, whether hybrid or all-digital, and we’re going to have to wait a good while before the jury comes back in on that transmission medium. But if we just consider the core, the analog signal and coverage that is universally receivable on any radio that features the AM band, I’d say that a bunch of AMs are worth saving, keeping and even improving. 

That said, there are economic considerations that we just can’t get around.

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Existential question

Over the past couple of years, I have been working to save one of our Denver AM stations that was losing its site. Long story, but it’s one you’ve heard time and again: The site owner wants to sell the tower site for development. It’s apparently worth much more with a different use than as the tower site for a couple of AM stations.

The author works on the 3D puzzle of component placement.

When we got a notice of lease non-renewal from the site owner a couple of years ago, we began looking for siting options. And in the discussions, the question persisted: Is this station worth saving?

I won’t go into more detail on those discussions but suffice it to say that we determined that the station has value, and with that in mind, we started looking at options, including moving it to one of our existing owned sites. 

Because of those economic considerations I mentioned, it turned out that really wasn’t an option. But we did find another home for the station just a couple of miles from the existing site. All it would take would be a diplexer to make it work with the 5 kW station that already called the site home.

Diplex equipment isn’t cheap. It requires vacuum capacitors, large coils and involves multiple cabinets. It didn’t take me long to figure out that a “store-bought” diplexer would not fit the budget for this station. Which left us with just one option: designing, building and installing our own diplexer, sort of the ultimate DIY project.

We love presenting DIY projects in Radio World Engineering Extra, and in our latest issue we hand you a doozie that we’ll tell in two parts. 

I’ll warn you, this kind of project is not for the faint of heart, and it requires specialized skills and experience to pull it off. Thankfully we were blessed with both.

The point of all this is to show that even big, complex, difficult DIY projects can be done with the right skills, tools and materials. And even if you don’t have that trio of required ingredients, if you have or can get two of the three, you can enlist some help for the other and still get it done. 

Keep that in mind when facing technical challenges going forward. Read our story here.