In Part 1 I showed that a cheap satellite upconverter can be used as a microwave downconverter with some mods. In this post I'll show you the modifications needed, step-by-step tutorial style, and make lame jokes. After more experimentation and burned fingers today I've found a more efficient way to do the mod that provides a much stronger signal at the output of the downconverter!
Soldering experience level: Moderate – SMD parts removal and fine soldering, but explained so the novice can complete it as well.
Some tools you will need are:
- Soldering Iron – Preferably with a very small tip. r
- Solder – I use Sn63/Pb37 RA type
- Tweezers – Fine tipped preferred but not required
- Needle Nose Pliers or Screwdriver to take the case and shield apart.
- Magnet Wire – 24 Ga or so. Tip: use unwound stranded wire in a pinch
- Wire Cutters
- Magnifying Glass or Goggles
- Exacto Knife
- Bright Light
- Volt/Ohm Meter to test for shorts etc.
SURGEON GENERAL'S WARNING: If you choose to use this information to modify your equipment you take all responsibility for any damage that may occur, up to and including the complete destruction of every device, computer, power grid, interplanetary starship, and/or non-gender specific restroom diaper changing station that may be in the vicinity. Also, I'm not responsible for you burning your own (or others – NTTAWWT) body parts or your wife's/husband's kitchen table. NOT MY FAULT!!! Besides, if you sue me you wouldn't get much. An old moody cat, some chickens that don't lay anymore, and some broken down ham radios. Continue at your own risk!
These boards are fairly forgiving so minor mistakes won't end your adventure. Just don't cross the streams when you can help it and don't hook it up to anything until the modification is complete. A general positive to ground short around the filters and such won't (shoudn't) kill it, but directly shorting the ICs on board or the regulator, well, no guarantees.
First we'll remove all the parts that are in our way. Filters, DiSEqC stuff, etc. In the images below, parts marked with a red dot or line are to be removed from the board. I've found that by heating one side of the smd parts with the iron and applying a little pressure they will "flip" up on the opposite pad. From here you can use your tweezers to pull them off or apply a little more heat to the bottom side of the part to get it to release. Sometimes they'll stick to the iron, just flick or gently scrape them off. Don't worry about losing the removed parts. We're not going to be reusing them here.
We'll start on the input section of the board. Remember red dots or lines are parts to be removed.
After you have removed those there is a capacitor under all that glue that needs to be removed. Also, in the lower right you'll notice a red dot on a resistor. Go ahead and get it off there too.
In the next picture you need to cut the trace where the red line is marked. You could cut it between the solder blob and the 101 marked resistor if you like, just to avoid cutting the hole trace that we'll soon need. I've found that if I scrape across there with the tip of an exacto knife it goes a lot easier, even rolling the sharp edge up and applying plenty of pressure. The red dot in the lower left is the same as the one in the lower right in the previous picture, just to avoid confusion. The red dot in the upper right can be removed now too or wait until the step after this.
There are four parts marked for removal in this image, including the one mentioned in the previous step.
TAKE GREAT CARE IN THE FOLLOWING STEP:
In this step you must VERY GENTLY bend the ceramic oscillator into an upright or leaning towards the IC position. The leads on this device are extremely fragile and it takes some force to bend it into an upright or forward leaning position. Take a small screwdriver or other tool, slide the tip in between the oscillator and the case, and gently apply pressure until it is in a position where you can use a finger tip to move it the rest of the way. It doesn't need to be bent all the way over, just enough to where you can safely reach your soldering iron tip to the board. If you move it around very much the oscillator WILL separate from the leads, so just get it into position and don't fool with it any more. We'll be coming back to this area in a future step. The first picture below is as it appears before adjusting the position.
And this is how it should appear after adjustment:
You've made it this far hopefully, now we begin wiring everything back up. For this part we'll need a small piece of magnet wire or similar about 12 inches (305mm) long. Cut it into pieces at the following lengths – leaving a little extra length on each for screw ups or mismeasurements. Two pieces at 2-1/2 inches (64mm) each, two pieces at 1-1/2 inches (39mm), two pieces at about 1-1/4 inch (32mm).
If using magnet wire or any similar type that has a hard (painted on) coating, grab your exacto knife or whatever is handy and scrape about 1/16th inch (or 3-4mm) back on each end to expose the copper for soldering. Take your 1-1/4 inch (32mm) piece of wire and on one end strip back approx 1/2 inch (13mm). Don't bother with the other end., we're using it as a handle/prop. Once you have that ready make sure your soldering iron is clean, get your solder and tweezers ready, and continue to the next step. From here on out, areas marked with GREEN DOTS are where we will solder. GREEN LINES are the wire jumpers we are adding.
In the following image the green dot indicates where you will place the 1 1/4 inch (32mm) piece of wire. You will slide it into the hole so that only the exposed copper is sticking out above the hole. If you have the converter laying flat about 1/4 inch of wire will stick up through the hole. If not, cut the wire shorter from the other end or slightly bend the wire to where it will stay put. Place a small amount of solder where the wire meets the board, taking care not to use too much solder or form an unwanted solder bridge to the adjacent ground plane. We're using this kick-stand technique because three other wires must be soldered here and it is very easy to bridge the solder or have the wires jump back up on you while adding the next. This makes it SO much easier, trust me. Once soldered into place flip the board over and apply a small amount of solder where the wire meets the board and trim the excess
This is the backside where you will solder and trim the excess. Once done flip the board back over and continue to the next step.
This image shows the beginning locations of where we are soldering from and too. Don't solder anything yet:
This next image shows the first three jumpers connecting the previously mentioned points. First take your 1-1/2 inch (39mm) wire and solder one side to the RF input, which is the big blob of solder middle far left. The solder that is there is nasty to get started so tin your iron tip a little to help the heat transfer fast. This is the most difficult part of the whole mod, solder (very little here) the other end of that wire to the capacitor marked in green in the far top left corner – solder it to the left side. Be very careful here as it is SO easy to create a solder bridge. If you have a solder sucker or solder braid you might keep it handy here. The wire should loop up a little bit once you're done there.
The next wire to solder is 2-1/2 inches (64mm) and starts at the left pad where I marked the capacitor for removal earlier. (The next green dot to the right of the RF input). Apply a small amount of solder to the pad, and place the wire before removing the iron. Stretch the wire out so it touches the kickstand wire. If it is way too long you can trim it some but remember to strip your wire back again. Don't solder it to the kickstand yet.
The final wire for this step begins at the bottom center green dot and you'll use the remaining 1-1/2 inch (39mm) wire. Solder one end to the bottom green dot and stretch the wire so it touches the kickstand wire.
In this step we'll attach the remaining 2-1/2 inch (64mm) wire and solder it and the other two wires to the kickstand. Be careful in behind the ceramic oscillator! This pic just shows the solder point behind the oscillator, the following picture shows this wire feeding back to the kickstand for soldering.
And the wire link:
Make sure to trim and scrape as necessary then solder all three wires to the kickstand – above board level so as not to bugger up the board or bridge to ground. Now is an excellent time to get your magnifying glass or goggles out and have a good look everywhere your soldering iron got near. Little solder balls can normally be popped loose with your exacto knife, but if necessary use the soldering iron and solder sucker or braid. Make sure you don't have any bridges to ground or other unintended traces. Only one more wire to go.
Flip the board over and solder the remaining 1-1/4 inch (32mm) wire as shown in the image below. This insures voltage gets to the PLL.
You'll need a bias tee that can provide 7-12v or so and feed from the SDR side (the side with the glued on cable). Make sure to hook your SDR or other radio to the correct side of the bias tee. You could fry your device, No fun!
Well, if you were able to stomach my rambling and you made it this far, Congratulations! You now have a microwave downconverter capable of up to 4.5GHz with an RTL-SDR dongle for much less than an expensive SDR. I make no claims on performance but it should be pretty decent considering the costs involved. Remember you'll probably need an LNA for many purposes in the microwave bands due to the low power nature of the services and the distances involved.
I hope this was helpful to you, if you have any questions I'll try to answer them in the comments below, on reddit, email, or whatever. I have 3 or 4 more of these laying here if someone needs one and isn't comfortable doing the mod themselves. Work out a trade or something. If you found this tutorial helpful leave a comment.
73's Chris – KD0CQ