Wednesday, August 19, 2009

Greg Fadick explains Marti RPUs

Here’s a bit about Marti units and a couple of pictures for you.

First is a picture of a late 60’s to mid-to-late 70’s Marti RPU. This is the vintage used at KAAY during that time, and at most every other station as well. In the case of news reporting, this unit would be mounted somewhere in the vehicle (usually the trunk) and a smaller remote control box (sorry, couldn’t find a pic of one of those) would be mounted under the dash with mic inputs and on-off controls.

Believe it or don’t, news was not the main use of these. Most stations put these to work for full remotes, as in do your whole show on location using one of these. If memory serves, one of this vintage was installed in the now-famous KAAY Funmobile (fondly referred to by some of us as “that frigging camper”). The antenna, which hasn’t changed much since that time, was mounted on a tall mast:

These units were highly directional, so you needed a direct shot back to the receiving dish at the studio, devoid of buildings, trees, small furry animals or whatever else. In fact, getting a “Marti shot” from any given location was iffy to the point that usually an engineer went out several days before the remote to verify a shot was possible. If not, then we had to order Telco loops.

Once you overlooked the fact that these RPU’s were about two feet long, a foot and a half wide, a foot or so deep and weighed about 40 pounds, you could call them portable. Some clients wanted the remote done from inside their store instead of from a remote vehicle, which meant you had to lug this monster in, set it up, then look closely at the floor and pick up any body parts that fell off of you while you were carrying it. They did, however, give you excellent audio quality.

These were also transmit only units with no provision for the studio to talk back to the remote. Most stations had some sort of system, like the one AJ and I had at KCLA, where once the Marti was powered up and transmitting, an indicator light in the control room would go on, letting you know to monitor what the jock at the remote was saying to you in cue. You then communicated with the remote jock by cutting the music on the air for a fraction of a second. The remote jock would say something like; “If you’re receiving me and it sounds good, give me one cut, if not, give me two cuts and I’ll go twist the antenna.”

These little transmitters also had call letters assigned by the FCC, and when you first powered it on and right before you powered it off, you had to give a station ID of the Marti. Not on air over the main transmitter, just over the Marti.

The other picture is a pair of early-to-late 70’s Marti STL’s. In fact, these are the exact model we used at KLAZ. They were low power, about 10 watts, reliable, and delivered incredible audio quality for the time. They only came in mono, so for FM stereo you had to use two of them transmitting on slightly different frequencies. In the picture, you’ll notice the front covers are missing. That was pretty much the standard way these were used, because with the covers on, they had nasty habit of overheating which would trigger a thermal protection circuit and shut them down. Not good when that happened right in the middle of Stairway To Heaven. Like the RPU’s, these were also assigned call letters, and had to be identified once per 24 hour period. If memory serves, KLAZ’s STL’s were WKQ-60 and WKQ-61. Amazing...this old mind remembers that, but I couldn’t tell you what I had for dinner last night.



  1. Wow! The size of a Marti is much larger than I imagined. I was asked to work on a remote unit for the local NBC radio station in Chicago about ten years ago. They were using a Motorola Maxtrac radio which normally runs about 5 KHz of FM deviation. It was built into a small case along with a twelve volt automobile stereo. The deviation was set to way above what I thought was the normal limit for that mobile transceiver. When I questioned the engineer, he told me that was normal for the frequency they were allocated. This package was taken aboard the traffic helicopters. The mobile traffic reporter would listen on the AM or FM band with the car stereo component, and he or she would know when to start the report. The whole package only weighed a few pounds. I'll bet things are even smaller now. I couldn't get any help from my coworkers because they were too busy drooling over the sexy female traffic reporter who brought the unit into our service facility. I wonder how small the current units have become? Anyway, the reason the units sound so good is they are/were running a wider FM signal than we would normally use for a typical two-way FM radio such as in a police car. Since they are allowed more bandwidth, this means they can have a better high frequency audio reponse.

    Ron Henselman

  2. Ah, the KLAZ Marti STLs. I believe Greg has nailed 'em, from the call signs right down to why the front covers had to be left off. For a while there, each day's program log began with the notation "Identify Microwaves STL."

    There was a small jeweler's screwdriver parked inside the bottom Marti in the stack. We used it to re-tune the unit (the slug was marked C2 as I remember) when it drifted off-frequency, which was at least once a day. No big deal, though. You'd just turn it one way or the other until the hash in your left ear went away.


  3. Putting those Marti STLs in the KLAZ control room was a bad idea - all mine. They should have been in the engineering closet or back in the air conditioning room. That studio was designed for a different room in a different building and was put together very quickly. I'm surprised that it worked for any length of time.

    That tall tower in the back was also a last-minute addition after Old Joe leased a studio building that couldn't see Shinall Mountain.