Repeater Pictures
I do not have pictures to show of our current installation, consisting of the 147.12 MHz repeater with its 900 MHz link to Phoenix, nor of pictures from the 449.20 MHz in Phoenix, but these pictures and those on the repeater front page represent the general installation of recent years, of the 147.12 and its companion 449.60, all taken by Neil Leverance, K9ZSR and possibly others.
The Stone Castle
This building was thrown up in about 1977 or 1978, and faced with river rock mined from the Salt River, adjacent to Blue Point Bridge on the road toward Saguaro Lake. My Dad and I got the rock in his 1972 GMC pickup, and I remember how we nearly got stuck with the truck loaded with rocks! (Some of you may remember Fred, KF7DF, Treasurer for many years for the club.) The repeater was a tube type Motorola Rack mount, with a 2E26 driver and a pair of 6146 in the final. It ran true FM and had a very good audio quality. There are no pictures from the era, or if there are, they were shot on film. There was no such thing as a digital camera.
During the early 1980's, I designed a controller that allowed disabling the timeout timer, and identified at most once every seven minutes and at least once every ten minutes, at the end of the incoming transmission, or at the point of timeout, and then only if there was use made of the repeater. Under normal operation, with a three-minute timer, this scheme always waited until the input signal was dropped and at least seven minutes had passed since the last identification cycle. If someone keyed just before the seven-minute timer expired and held the key down for a full three minutes, just short of timing out, the identifier would sound at ten minutes past the last cycle. And if the station stayed keyed for say, four minutes, the identifier would run at the point of timeout and then drop the repeater until the next reset. The identifier was guaranteed to run at the end of ten minutes.
Also at this time, I was stuck with sending code practice every week after I volunteered to relieve Bill Falk, K7WJF, one night when he couldn't run code practice, and I turned the matter over to my Radio Shack Color Computer 2.
With the timeout timer off, and my computer-generated code practice timed to run somewhere between at least seven minutes and no more than ten, my signal dropped, let the repeater air its identification, and resumed the next code practice segment after the identifier. With this setup, I began running 5 through 20 words per minute practice for upwards of an hour after the Wednesday net while I got caught up with the newspaper!
The Stone Castle housed a four-cavity duplexer in the corner, together with a rack-mount tower for the repeater equipment. Later after we retired the tube gear, the repeater sat on top of the duplexer.
Later, we added an isolator, which is a device that has three ports on it. They are transmitter input, antenna output and dummy load. This thing resembles a traffic circle, or roundabout for RF. Signal entering from the transmitter is routed clockwise 120 degrees to the antenna port. Incoming signal from the antenna, instead of being allowed directly back into the transmitter to mix and cause spurious frequencies, entered the antenna port and was routed another 120 degrees to the dummy load, where it was dissipated, while potential input from the dummy load would complete the circle with a rotation to the transmitter port. Of course, there is no signal input from the dummy load port, so the transmitter has been isolated from incoming signals.
Prior to our use of this device, we often had a strong signal from a user on 146.52 come in and mix with the transmitter's second harmonic while the transmitter was keyed from some regular event on the repeater, like if someone kerchunked the repeater or the identifier came on. The difference frequency of (2*147.12)−146.52=147.72, with audio from 146.52 mixed with double-strong audio from 147.12 appearing on the repeater input frequency, which would keep the repeater keyed (with a lot of feedback) until the 146.52 signal quit transmitting.
The picture I have up is of a second-harmonic filter, which isn't quite the same thing. Similar, except that off to the side would be a ten- or fifteen-watt dummy load, square, or rectangular shape, with a bunch of cooling fins, color black, where that little gold thing is on the side. A check of EMR's web site on Google came up with about fifteen missing documents relating to isolators or circulators, so I couldn't borrow a picture.