What Does Your Modern Homebrew Look Like?

And this reader says digital and analog radio are like oil and water
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MODERN HOMEBREW

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Responding to “Doesn’t Anyone Build Anything Anymore,” RW Oct. 25 issue:

Like many, my first brews were HeathKits, Eico kits and Knight kits, then the carrier current AM 6146 transmitters in my college radio station.

With a background in homegrown amateur radio gear (Rochester VHF group president, home-made 2m FM, [single] sideband and test equipment), I went to HCJB to build the HC100 series transmitters. I was responsible for the DSP solid-state modulator.

Now I am doing FM again, and find the need for FM “heat maps” simultaneously recording the signal strengths of multiple FM stations on the same channel as a function of location to combat the rampant piracy on today’s FM band. The prototype uses a Raspberry Pi and laptop, but the distributable units will use an Android pad or phone. The detector is a USB RTL stick. Directivity is provided by an electrically rotatable four-square array on the car roof, which can also serve for a Doppler DF system when only one signal is receivable.

Bob Moore, WB2L
Indiana

It was in the early ’60s, as I recall, at station WRKT(FM) in Cocoa Beach, Fla., when the FCC was requiring stations to carry news in addition to their regular programming. Our FM station was automated with a Schafer 800 system, nothing digital about it. The station didn’t have the money to buy their network joiner from Schafer, so I was faced with finding a way to “make it happen.”

The only thing I had to make the station ID was a reel-to-reel playback that we had been using to give time breaks (a Schafer unit) which I converted to have the station IDs on. How to cue it ... the only thing available was the Schafer one-hour timer that ran the whole system. I took my cue from that to start the tape deck to provide the station ID, then to switch the audio from automation to NBC for the news. I built a two-step switch that dropped the audio level in 3 dB steps to fade the automation to NBC. When the news ended (five minutes), the timer cued the two-step switch to go back to the automation.

The only problem I had with the system was on the weekend when the NBC announcers jumped in too quickly after the news ended (didn’t happen all the time); they were supposed to wait a few seconds to allow stations not carrying the “weekend show” to make a clean break. The two-step faded them just fine, but it didn’t sound good. Complaints to NBC helped only a little. I think it was Harry Morgan who was the worst about that; jumping the gun.

The station ID was recorded on the reel to reel Schafer “clock” tape that had “windows” in the tape that allowed the photo cell to stop the machine after the ID and be cued for the next break.

The station had the #2 rating behind a local top 40 and ahead of its AM counterpart. Not bad for a non-live radio station with only one recorded voice, 24/7, excepting the commercials. The engineer (me) was that voice, although I think it was my wife who recorded the IDs!

Mark Manucy, W4FJE
Orlando, Fla.

DIGITAL AND ANALOG DO NOT MIX

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Due to the way that IBOC technology works, stations that choose to use the tech essentially send out their original analog broadcast with two digital “sidebands” at the bottom and top of their allotted frequency.

If the power allotted is enough to bleed into the adjacent channels in the frequencies immediately above and below the station that is utilizing IBOC, even if the digital signal is too weak to be received on a digital radio, it will still cause interference to an adjacent analog channel.

This is causing interference and destroying the listening experience for anyone who attempts to tune into those stations. In the same way that the digital sidebands can bleed into adjacent frequencies and cause interference, they can also interfere with their own associated analog signal.

This is a pretty big problem, since one of the most important selling points of IBOC is that it allows digital and analog signals to share the frequency once occupied by only an analog signal. It is also a kind of Catch-22, due to the fact that a low signal strength results in an HD Radio broadcast that nobody can receive, while a strong one can interfere with the analog signal, which is the one that almost everyone is actually listening to in the first place.

I am an LPFM operator experiencing severe noise from these very high power stations 80 miles away! Many complaints from listeners hearing noise on my frequency. Many analog stations are unaware of this interference because it masks itself by just inducing white noise, noise that you would normally hear on a vacant frequency. Many of the stations I listened to are no longer available due to digital radio.

Digital does not belong in an analog band!

Frank Vela
WFJV(LP)
Citronelle, Fla.

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