SoftRock 6.3 RXTX Transceiver Buildup Journal

[KT6F]

I'm ready to begin the buildup of the SoftRock v6.3 RXTX+Xtall Transceiver Kit with Si570 and RX BPFs. This build will include PA/Filters for all ham bands from 80 through 10 meters. Peripherals include the Electronically Switched BPF Kit and the USB I2C Interface Kit.

There are a LOT of components here and the number of transformers and coils is daunting. I'll start by mounting all the SMT components and go from there...

[KT6F]

Here are the mostly unpopulated SoftRock 6.3 RXTX circuit boards. I previously mounted the SMT components on a couple of the PA/Filter boards as well as the ABPF board. I'm going to sit down here and mount the rest of the SMT components now and will post another picture of the SMT populated boards...

[KT6F]

The remainder of the SMT components have been mounted and I'm ready to work on the through hole components. As usual, solder paste produced excellent professional looking results.

I had to search around to verify that I was mounting the SI570 with the correct orientation. The rule of thumb is that while holding an IC so you can read the print, pin one is always the first pin at the lower left. Most ICs have a mark, but I didn't want to take any chances with the SI570. There was a tiny dot at the lower left. Checking at wb5rvz.com verified it.

[5/19/10 Edited to add; Be sure to use appropriate ESD (electrostatic discharge) prevention when handling your board from here on in. The mounted IC components may be vulnerable to damage.]



Summary of solder paste method I use (added on 5/19/10)...

Small quantities [a syringe containing about 0.5 cc] of normally expensive solder paste may be purchased at http://www.kd5ssj.com/index.php?opti...=120&Itemid=54 for about $5.00. .5 cc goes a long way. I've built six kits with one order of solder paste and there's plenty left for more. Be sure to keep it in your refrigerator as the shelf life is less than a year I believe. It lasts longer if kept cold.

I use the heat (embossing) gun on top of a cup warmer method. The cup warmer is not absolutely necessary but speeds up the process. The method probably warrants a separate thread but here's a rundown.

Apply very small dabs of solder paste to your circuit board wherever an SMT component will go and carefully press each component into the paste. See the article on Yet Another Vacuum Pickup Tool, Lightweight &.... I usually apply components in several rounds, grouping them geographically on the board. Lay the board with the unsoldered components on the warmer and let it heat up for a couple minutes. Turn your embossing gun on and hold it nearly vertical a couple inches above the components. Move the gun around slowly until you see the solder suddenly begin melting and becoming shiny. Be careful not to blow components out of place with the heat gun air. One of the side benefits of the solder paste method is that components automatically slide into the center of the pads which results in very straight layout.

I'm a GW (Goodwill) fan and I see cup warmers both new and used there for two or three dollars all the time. The embossing guns may be purchased at hobby and craft stores for around $20.

[KT6F]

Presorting components saves a significant amount of time usually required to populate the board. Now I'll load the caps according to their reference number and solder away...

[KT6F]

All the ceramic caps are inserted and waiting for solder...

[KT6F]

Ceramic capacitors are all soldered in and trimmed, quick and easy...

[KT6F]

The electrolytics are all soldered and trimmed. Time to take a break and watch Last of the Summer Wine...

[KT6F]

I presort the resistors to speed up mounting time. Some resistor color codes are hard to distinguish, particularly the red and brown. I measure every resistor to verify it's value.

[KT6F]

All the resistors are placed and ready to solder. I find it much faster to load the whole board before soldering. I begin soldering leads that are easy to get to close to the board edges and work my way around, straightening them as I solder. Then I clip everything that's soldered and go around again. I continue until all joints are soldered and clipped.

[KT6F]

The resistors are all soldered on and clipped. There aren't many difficult solder joints to get to so this is a pretty easy build so far. I'll mount the transistors and transformer tomorrow. Then I get to enjoy the most excellent task of winding coils and transformers for some of the BPFs and perhaps a PA/Filter or two...

[KT6F]

I completed mounting the transistors, jacks, and DIP switch. The identifying mark on Q2(2N3906) was too dim to read but process of elimination verified the number.

[KT6F]

The last component to mount was RFC1 on a binocular core. I reamed the holes in the core out with a small drill bit as always. This removes sharp edges that tend to strip the insulation from the magnet wire. The last turn of the windings was difficult to get through the hole past the first turns and took a little careful perseverance.

Stripping coil and transformer windings is probably my most dreaded task. So I decided to try a different technique. I fired up the Dremel with a fine stone and carefully stripped the insulation. This worked very well, so I'll probably use it for all the coils I've got to wind.

[5/19/10 Edited to add; Tony has indicated that the magnet wire in the SoftRock kits is the type that the insulation burns off of with a blob of solder on a hot tip. I've used heat stripable wire before and it's very convenient. The technique hasn't seemed to work with this wire. I suspect I didn't use enough heat and should have turned the iron up all the way. I've got some coils to wind today and will try it.]

[KT6F]

I completed the 80/40 meter BPF (band pass filter) board (small board shown plugged in the lower edge of the main board). There was one gotcha there. I'm used to winding coils that mount vertically and followed suit with this one. But of course, when it came time to solder it to the board, the leads came off the wrong place for a horizontal placement. So a little creative routing of the leads was necessary to make it work...



Note the uncompleted PA/LPF board parked at the upper edge of the board. I'm about to wind the six coils for that one next...

[KT6F]

A rainy cool evening, 40 meter chatter in the background, a pot of hot coffee within reach, and me sitting here winding coils. What could be better?

[KT6F]

The 80/40 meter PA/Filter board is complete. Those binocular core transformers were no fun to wind. One more turn wouldn't have fit. If you follow the instructions for winding the coils at wb5rvz.com, be sure to cut the #26 wire longer than instructed. I usually end up with a long lead at the end so I cut wire just slightly longer than specified. That was ok for the #30 wire. But the #26 wire just barely left enough for the leads when I was done.

[5/27/10 Edited to add] I've had a lot of fun with the 6.3 the past few days. But the fact that 40 meters seems to be dead most of the time has been eating at me. I tuned around on a different radio and found that there were indeed signals on 40 that the 6.3 wasn't hearing. So I double checked winding counts on the coils that are able to be counted while mounted. Surprise! L201 and L202 on the PA/Filter board had way more turns than called for. A little detective work revealed that I had wound them according to instructions for the external LPF for 80 meters that comes with the 80/40 PA/Filter kit. Rather than the 14 turns called for, I incorrectly wound them with 25 turns. That effectively lowered the passband for RX through that board and pretty much took out 40 meters. It was easy removing the extra windings and remounting the coils. Now I've got signals all over 40 meters. That was why the specified length for the #26 wire was so short...

[KT6F]

I finished mounting the headers on the board and cleaned off the resin residue. I performed an abbreviated inspection of joints and orientations. One more meticulous inspection and it will be ready for the smoke test...

[KT6F]

Next, after testing the radio to make sure it works, will be the buildup of the rest of the PA/Filters and BPF boards.

I've decided more or less to interface the ABPF kit and I2C with the 6.3ng I've got waiting in the wings. I've also got a frequency generator/controller w/display on it's way to use with the ng.

[KT6F]

SoftRock Final Exam...

I always try to remedy problems as I go and try to maintain a presence of mind that will prevent later issues. But, a meticulous examination of every component and solder joint is necessary for a successful build. You must make sure that every joint is solid and that there is no conductive debris on the board, including solder where it's not supposed to be. By this you eliminate the most common causes of failed builds. Of course, if there are any faulty components in the kit, you're at their mercy. Otherwise these kits are extremely well put together and proven. So theoretically, if everything is in the right place, and the construction is clean, you'll have a working radio without fail.

A few tips...

Use solder resin remover to clean the resin mess off the board.
Use a strong illuminated magnifier for close examination. Mine is on a flexible arm mount and clamps to my desk.
One negative aspect of solder paste is that if you leave any paste where there is not supposed to be solder, it will happily create extraneous solder blobs and whiskers. They especially like to hide under ICs. So a large safety pin works great for picking at solder connections and potential microscopic solder blobs and whiskers. Make a special effort to turn the board at such an angle to enable looking between the pins under components.

An ohmmeter is a good tool to use for testing questionable solder joints and possible bridges. The last thing I check with the ohmmeter is the resistance of the power connection and rails. The 12v power connection measured at about 15 megohms. The 5v test point measured about 900Ω. If you see continuity or a low resistance, DO NOT PLUG IN THE POWER. Look for shorts or incorrectly oriented components.

Double check component orientation. Yes, I do that when I mount the components originally, but perhaps I hadn't had enough coffee during a session and blanked out. Check pin one on all ICs. Make sure the resistors are all in the correct holes by checking those little lines screen printed on the board. Pay special attention to diodes and transistors to make sure they're oriented correctly. And check electrolytics for the absence of the negative stripe next to the plus signs screen printed on the board.

And lastly, I take the board out to the garage and hit it with compressed air (carefully) to dislodge any debris I may have missed. So far all my SoftRock projects have powered up the first time using the construction methods and techniques posted above. Hopefully this one is no different.

Remember, Murphy IS NOT your friend. Break the law!

[KT6F]

Here's the final exam score, A+. As you can see below the radio came on without any issues. Another perfect score thanks to Tony Parks and his excellent SoftRock design and kitting. The image shows 75 meters during the daytime when all I usually get is noise.

SoftRock 6.3 RXTX observations...

The receiver seems significantly more sensitive than the 80 meter SoftRock Lite II. Head to head comparison indicates at least a 10dB gain in noise level in the same frequency range. Increased noise level usually translates to increased signal reception. The only problem is that I'm seeing a big spur or harmonic on 40 meters from an AM broadcast array that's about a mile from here. It wasn't very noticeable on the Lite II receivers. Perhaps getting the radio into a shielded case will help.

I'm loving the absence of that center spike. It was pretty small in the Lite II version, but this one is practically nonexistent.

I'll have to wait until tonight when 80/40 open up to see how ham signals do. Until then, to work on more BPF/LPF boards for the higher bands...

[KT6F]

Well, 40 meters wasn't good last night so dropping down to 80/75 meters saw some action. Both audio and senisitivity were very good. I have some work to do on connections so I can transmit, but first I'll build the 30/20/17 BPF to see what I can hear during the day today. But according to http://www.spaceweather.com/ there are still no sunspots, so the outlook is pretty grim.

But first... a little business to do and have to get the coffee on...

[KT6F]

Some kit builders may not realize that you can't receive on bands that you don't have a Power Amp/Filter board for. I didn't. I built the 30-17 LPF yesterday thinking I could receive on those bands with the 80/40 PAF plugged in. Wrong! There's more than just antenna interaction going on there. I had previously skimmed the schematics to see how the filters interact but didn't see anything obvious. You must plug both the boards in for the band you want to listen to. So if you didn't buy all the PAFs, you won't be receiving all the bands.

I worked until after 2:00 AM this morning on the 30/20/17 PAF board. These boards are projects in and of themselves. They are very labor intensive. The binoculars are difficult to wind and the three transformers are hard to mount if all the other components are already mounted. But I don't want to mount any of the coils until last because there's a risk of breaking one off the board just from handling.

So, I slept in a little and need to get some coffee going. Then I'll mount the L coils on this board...

[KT6F]

And by the way, I used heat to strip the coil leads this time. A hot iron is the key. I turned the iron up all the way and the insulation burned off easily. Made kind of a mess that had to be removed from the wire. I just used my fingernail. Oh yeah, my coffee...

[KT6F]

The 30-17 meter filters are plugged in and pumping, but the bands are in awful condition. We're still sunspotless. It's like being all dressed up with no where to go...

[KT6F]

5PM PDT and 20 is finally opening up [sort of] with a few strong SSB signals + QSB. The 6.3 is sounding good...

[KT6F]

This thread is continued in the The USB I2C Controller - The only way to go! thread...