Home Brew Things
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Contents: Basics; Supplies; Antenna Control; The Simple Rocker Switch; Debouncer; Antenna Switch; Remote Control; Other Things; Conclusion;
Some might argue, but the art of home brewing (we're not talking about beer either!) is not dead; it's just evolved! Back in the old days, it was the rule (not the exception) to build your own gear, including transmitters, receivers, antennas, and even test gear. Nowadays, that part of the hobby is all but gone. However, there are other things we can build which will make our life easier, safe us a few dollars, and yet provide us with nearly the same level of pride the old days offered.
What we'll tackle here does require some mechanical and electrical ability, and at least some measure of hand tools. You don't need a drill press, but it would help to have one. You'll need a soldering iron (leave the gun at the door), screwdrivers, needle nose pliers, cutters, and the ubiquitous DVM (digital voltmeter). Of course, if you don't own any of these things, it might behoove you to remain an appliance operator, but that's not the essence of amateur radio!
Ignoring the expenditure of the aforementioned, what follows will easily save you 50% if you're frugal, and perhaps more. If you buy everything new, you might not save a dime. However, the experience you'll gain is worth something, and let's don't forget the pride factor either.
There are a myriad of links on this site of interest to amateurs, no matter their interests. Since we're talking about building, here are a few sites of specific interest to home brewers, tinkerers, and most amateurs.
Aaron's General Store carries a large stock of both inch and metric sized bolts, nuts, washers, and fasteners. They even have a line of security fasteners of just about every configuration you can think of. If they don't have it, you probably can't find it anywhere.
Grumpy Shop is another good supplier of esoteric things. If you're a home brewer, they're worth a visit.
Speedy Metals is a supplier of aluminum and stainless steel rods, tubes, and bars.
Micro Fasteners is a great place to visit if you need set screws, and fasteners.
All Electronics, and All Spectrum Electronics, both carry new, used, pulls, and overages of electronic parts, connectors, LEDs, fans, you name it.
Mouser, Newark, and Digikey are all first-line retailers of all things electronic.
There is an article within these pages about home brewing your own antenna. For whatever reason, it is the 6th most-popular page. I suspect the popularity is due in part to the high cost of procuring a decent-quality mobile antenna. Purchased new, remote controlled ones begin at about $400, and extend to well over $1,000. Add in a few requisite extras, and you're well into the $600 range. That's big money in most amateur circles.
Part of the procurement costs are wrapped up in the control circuitry. For example, a BetterRF automatic controller costs about $150 including shipping, and it only works with an Icom 7000. If you own one of the other brands of HF mobile transceivers, you're pretty well out of luck.
MFJ/Ameritron does make several models, starting at $100 or so. The MFJ-1926 (shown right) moves the antenna to a predetermined point, but fine tuning is by manual control. It also requires the use a reed switch (usually optional), and if careful attention isn't paid to choking the RF off the control leads, the position counter will be erratic.
Adding a little insult, manual controllers often sell for $70 or more, and basically they're not much more than a DPDT switch. Manual control does have a few drawbacks. One, you have to keep an eye on your SWR readout as you adjust the antenna, and this can be very distracting (dangerous actually) while you're under way. In some cases, an external SWR bridge or wattmeter is required. This is true of the Icom IC-706 if you trick it into thinking an AH-4 is connected (10 watt carrier), as it takes about 30 watts before the built in SWR meter will operate.
As long as you're willing to put up with these inconveniences, building a manual remote control is very easy. With a little extra work, you can build in an EOT (end of travel) indicator, and for a little more work, you can tell your Icom IC-706 to transmit a 10 watt carrier.
What you see here isn't original, as remote control antennas have been with us for many years. The circuitry isn't patented, there's nothing special or exotic about it, and you can easily duplicate the effort. How much you spend depends a lot on how fancy you want it to be.
The simple looking rocker switch shown at right is an i-Box (about $75) from High Sierra®. It consists of a DPDT rocker switch, and configured as (on)-off-(on). The parentheses indicate a momentary (spring-loaded) position. Pushing the switch causes the antenna to move up or down, but that's not all. Inside are a few more components which tell the Icom IC-706 to transmit a 10 watt carrier. It has a couple of drawbacks.
Power for the unit, and the antenna, comes from the Icom's tuner or accessory port. Icom specs clearly state that the maximum current draw is one amp, which is easily exceeded if the antenna stalls at one end. If the supply is shorted, for whatever reason, a circuit trace will often fail before the internal fuse blows. The controller has an indicator which lights up when the end of travel is reached, but this doesn't eliminate the problem. It can be prevented by using a RigRunner® or similar power block to power the antenna, but does require rewiring the i-Box, which would negate the warranty coverage.
Using the 706 version on an Icom IC-7000 isn't something you want to do either. Although the unit will indeed work on a 7000, it stresses an open collector output inside the main CPU, and can cause it to fail. High Sierra does make a unit for the IC-7000. In this case, the switch not only operates the antenna, it keys the radio's PTT. You have to switch the radio to the AM mode in order to transmit a carrier in this case. We're going to use this idea, but in a slightly different way.
Here is the schematic of a similar manual control (click to enlarge). The LED can be any color or size, and the transistor can be almost any NPN, at least equal to a 2N2222. The resistor labeled See Text needs to be selected for your antenna. For most remote antennas drawing up to 500 mils of run current, a .72 ohm, 2 watt resistor is close enough. If you have trouble finding one, then use three, 2 ohm, 1 watt resistors in parallel.
All of the components can be mounted dead bug style in a plastic case. If you don't use a RigRunner® to power the unit, rather than use a fuse holder, just use two insulated, 1/4 inch spade lug connectors and an ATO (automotive) fuse. As I stated above, the switch needs to be an (on)-off-(on), momentary type, but almost any style switch will do. Mouser is a good source for any/all of the components. If you're resourceful, you can build the complete control for less than $15.
Once completed, and wired, simply switch your transceiver to AM, push the microphone PTT, and move your antenna with the rocker switch to resonance. Again, this requires you keep an eye on the radio's SWR readout, so you should avoid tuning the antenna when underway. If the LED lights, it means you've reached the end of travel for that direction.
Digressing for just a moment. Using a single switch to move the antenna, and key the radio like the 706 i-Box does, presents a major drawback. As soon as you let off the switch, the carrier stops. Since most remote controlled antennas have some over travel, this makes finding the resonant point much more difficult than using PTT, especially on 80 meters where antenna tuning is very sharp!
I mentioned above about properly choking the RF off of the control leads. How that's done is located here. Sometimes, even if you do a good job of building the choke, you still get miscounts on controllers which use a reed switch. The reason is, most antenna reed switches only switch states (off to on, and back off) for only a faction of a second; typically less than 100 msec. Even though the logic is fast enough to catch the pulse, capacitance in the wiring, and a little residual RF, can cause a miscount. There is a solution.
The schematic shown left elongates, and debounces the pulse. The size of the capacitor varies depending on the controller, but usually a .5 uF or 1.0 uF is large enough. You don't want one too big or the count will be missed altogether. Just about any small, 12 volt, low power relay can be used. You should select one with a coil current of less than 200 mils. The diode can be just about any 1 amp power diode; 1N4008 for example.
You'll need small plastic box to put it in, and a few other minor hardware items, but your miscount problem will be solved. This assume, of course, that you have properly choked the common mode from both the control cable, and the coax.
Modern mobile transceivers are often referred to as DC to daylight radios, because they usually cover 160 meters through 70 centimeters. Being as small as they are, there isn't a whole lot of room for antenna connectors. Quite often, the output connections are on dongles; the Kenwood TS-480 is a good example. In most cases, only two connections are provided. One for 160 through 6 meters, the other for V/UHF. If you use separate antennas for VHF and UHF, diplexers are available to split the one port into two. However, if you use a separate antenna for the HF bands, and another for 6 meters as I do, you need an antenna switch. This begs the question, what do you do if you're transceiver is remotely mounted? You can buy 12 volt powered, remote antenna switches like the MFJ-4712 ($80), but you will need to modify it for mobile use. The solution is to make one, and if you're frugal, it'll cost you about $20.
The left photo (click to enlarge) shows the inside of the switch. It seems simple enough, but there are a few caveats. Knowing how it was made should put you over the hurtle, so to speak.
The box is Hammond cast aluminum one, about 3x4x2, although just about any aluminum or steel box could be used. The relay is a DPDT, removed from it's plastic enclosure, and screwed into the bottom of the box. The flexible white wire (the common connection) originally connected to a terminal on the opposite end of the relay. The poles were wired in parallel, and to the output SO239s with short pieces of #14 copper wire. All of this was done to keep the insertion losses low. Even then, the throughput SWR rises slightly (1.2:1 at 54 MHz). The SWR bump might have been smaller had I used a smaller box, but it was what I had on hand at the time.
If you look closely at the expanded photo, you'll notice a diode and small cap attached across the coil terminals. These are added to eliminate the back EMF when the switch is turned off, so connection polarity is important. Power is fed to the switch from a front mounted control panel, shown at right.
There's a little more behind the remote control shown in the photo above right. I explain what it does in my Amplifier Care & Feeding article, and I've included the schematic here.
The front mounted switch (left in the photo) is the amplifier control switch depicted graphically in the schematic. The rear switch is a DPDT (On-Off-On), and has two functions. When the switch is forward (as shown), all systems are off. When the switch is in the center position, it activates the video coming from the Icom IC-7000, and applies it to the TVandNav2Go video converter. When it is moved to the rear position, it also activates the aforementioned remote antenna switch.
There's a lot more to this remote control than meets the eye. It also brings power to the passenger cabin to power not only the voltmeter shown, but also my SCAF-1 filter. The interconnecting cable is a 12 conductor, #20, with shield. While overkill, it allows room for future additions. There are Molex connectors on both ends for ease of installation. It should be noted that powering the radio, amplifier, and the ancillary devices from the same power and grounding source eliminates ground loop problems.
By the way, the video converter isn't really needed, as there is a way to feed composite video directly to the Navi unit if it doesn't have a backup camera included. However, it requires tricking the Navi into thinking the vehicle is in reverse, which requires tapping into existing wiring. The converter does have an extra benefit, however. There are actually two inputs, so you can add a backup camera if you wish. Or, you could hook up a DVD player, albeit illegal while underway.
Every now and then, every piece of amateur gear has to be worked on. Or, if you're like me, you experiment a lot. The box shown at left, contains a reboxed BetterRF antenna controller, hour meter, indicator LEDs, and all of the interconnecting cables. The Molex at the top of the photo is the cable to the front-mounted control box shown upper right. The smaller Molex on the left goes to the antenna motor, and the other Molex is the power and control wires from the IC-7000's Tuner port. There is also a cable going to the remote port on the SGC SG500 amplifier, which includes a fuse holder (bottom left). As mentioned above, it is only a pair of 1/4 spade lug connectors, with an ATO, 3 amp fuse plugged into them. The box is held down to the amplifier via existing 8x24 tapped holes which hold the cover on.
Out of the photo, and behind the amplifier is the main body of the IC-7000, which is bolted to the SG500's optional cooling fan assembly. The complete package is held to the trunk floor by two brackets. Remove the bracket hold down knob nuts, 8 connectors (two coax, three Molex, Icom remote cable, and two 120 amp PowerPoles), and the whole assembly can be removed, and set on the work bench in less than a minute.
Before you start tearing your stuff apart to rebox it, you need to know a few things. First, the warranty is gone! You'll need schematics, a DVM, more than simple electronics, and the necessary hand and power tools. Cost is also an object. The box, it's innards, the various connectors, Zener diodes (meter protection), caps, and hardware all come to about $350. If it doesn't do anything else of benefit, it is convenient when service is required.
Since you ask... the hour meter reads just over 800 hours. This is the amplifier's on time, not transmit time. I must admit, that the ratio between the two meters (one for total, one for key down) might have been telltale. I guess that's the next addition.
If you have multiple radios in your vehicle, you might want to read this section of the Audio, Filtering, & Speakers article. It describes how to add multiple inputs to an amplifiers speaker.
There is a lot more stuff you can build to make mobile operating easier, and safer. Phil Salas, AD5X, has a bunch of projects listed on his web site. If you own a 706, look at his Tenna-Tune project. With a minor change or two, you can even use it on an IC-7000.
Good luck with what you do to make your life easier.'