I've finally completed my switch box project. The story behind this project is simple, need is the mother of invention. About a year ago, I thought how convenient it would be to have the ability to switch my station's PTT and ALC lines with a simple switch box. I searched the Internet for something commercially available to perform the task. However, I was unable to find anything that would easily accomplish this feat. Therefore, I decided to design and construct the device myself.
Anybody who owns multiple transceivers and amplifiers, knows the hassle involved when switching out multiple PTT and ALC lines (when required) from an amplifier or transceiver every time you want to change your Station's transceiver/amplifier configuration. Not only is it a hassle, you also take a risk that you may scratch or otherwise damage your gear just by the constant handling.
In designing this project, not only did I want the ability to switch my PTT and ALC lines, I also wanted to have a few additional features that I thought would be useful to me. Not only does this device allow the station operator to switch the PTT and ALC lines among 6 different transceivers and amplifers, in any combination. It also includes a convenient programmable 10 minute ID reminder, and adds the ability to key any transceiver/amplifer combination with a hand switch, foot switch, by computer, or any other way that utilizes simple low (grounded) or positive activation. This device, although not perfect, I believe gives the most flexibility in the ability to configure a station's transceiver, amplifier, and keying mechanisms, with the most ease.
I tried to logically layout the controls on the front panel in a sequence that they would be used. The control functions on the front panel are broken down into 6 sections, from left to right, and the configuration is as follows:
The first section controls which device or source controls the PTT keying for the station. The first selection is Transceiver. When using the Transceiver selection, it allow the operator to choose from one of six transceivers to key one of six amplifiers, such as when using a microphone that is plugged directly into the radio, which would key both the radio and the amplifier though the amplifier buffer.
The second selection is hand key, with this selection you can use a simple hand switch to simultaneously key one of six transceivers and one of six amplifiers, in any combination that you may choose.
The third selection was specifically designed to utilize a Heil Brand Foot Switch, which uses two control lines consisting of a 1/4 inch phone plug for transceiver keying and an RCA plug for amplifier keying. The Heil foot switch includes a mechanical delay to allow the amplifier to be keyed first, the switch box accommodates this feature, and the other keying sequences by utilizing two independent optical keying buffers.
The fourth selection is Auxiliary, this selection allows for use of any other type of switching mechanism that someone may want to use. This selection functions similar to the function of the hand switch selection, but it is independent. As an example, you could conveniently hook up a straight key to the auxiliary jack to operate both a transceiver and amplifier in QSK.
Although not located on the front panel, there is a fifth keying option that is available to for use with a personal computer. On the rear of the control box there are two RCA jacks (one for each optical buffer) which will allow keying of either a transceiver and/or an amplifier, independent of the front PTT source selection. Utilizing the jacks on the rear of the box which are marked Computer T/R, activation will occur if the signal goes high (positive) instead of low to ground.
The second section on the front panel is identified as Transceiver (PTT), with this switch you can choose which of the six transceivers will serve as the PTT source to key one of six amplifiers, but only if transceiver is selected in section one. If transceiver is not selected in section one, the selections made in section two are inactive as far as utilizing the internal optical buffers.
The third section is marked Transceiver (Remote), and serves to allow selection of which transceiver will be keyed with the PTT sources selected in section 1 or by computer keying, again except transceiver. If transceiver is selected, this feature is inactive.
The fourth section is Amplifier (T/R Relay), this section allows the selection of one of six different amplifiers. This feature is available at all times.
Sections 5 and 6 is for Automatic Limit Control (In) and (Out), and is configured as two switches, back to back that share a single common signal path between the two. Basically, these two sections allow you to choose the ALC signal from one of six transceivers to be directed to one of six amplifiers. In hindsight, it may have been better to make the ALC selection (In) automatically follow the Transceiver selection in section 2, and the ALC (Out), follow the Amplifier selection in section 4, but I did not want to complicate the switching matrix any further. The downside is without the automatic coordination, it is possible to drive excessive watts into an amplifier that may be damaged when the ALC selections do not correspond to the Transceiver/Amplifier selections. This is especially important on the newer solid state transceivers, such as the Yaesu Quadra that is part of the station at AB4D.
The heart of the control box is the two optical keying buffers. I obtained these devices in kit form from www.hamgadgets .com. The buffers have two inputs (low and high) and one low output for amplifier or transceiver keying. An additional feature of the control box also consists of two additional ham gadget kits, a 10 minute ID timer and a connection kit. The ID timer can function as a simple ID reminder, which is how I have it configured, or it can also be made to key a transceiver and provide an audio signal consisting of text in Morse code, such as your call. The timer would be idea for use as a master ID unit in a repeater. The connection kit includes an audio amplifier which smooths out the square wave audio signal generated by the timer circuit.
I have been using the key box in my station for the past several weeks and it is working as planned. I had an issue at first with the ID timer, in that once you changed the 10 minute alert from a series of beeps to CW, it affected the default timing sequence. After adjusting the timing sequence from 600 seconds to 596 seconds, the timer began to give an alert exactly every 10 minutes.
Here is a photo of the switch box in operation, if you would like more information concerning this project, feel free to email me at firstname.lastname@example.org