The 147.120 Tech Net Blog

Well, mostly conquered
 
Jim has a capacitor that is way more than 50 PF. So it’s time to learn series and parallel capacitance, resonant circuits and probably something else. No, I’m not going to dive into it here, admitingly I have to learn that myself! However, there do seem to be some calculators out and about that should help.

As you can see in the picture his VFO covers a lot more than just the 20 meter band. For some that may be just fine. What it does, though, is limit the ‘resolution’ of your tuning dial. The radio does have a nice fine tune adjustment to compensate for that.

 
Another big breakthrough at the Party was the flashing of Das U-Boot. Yah, we have flashing Das U-Boot! Dave sucessfully formatted an SD card the way the NGW100 likes, we moved the Atmel Flash Upgrade Utility to the SD card, and told U-Boot to load the image. It was cool! Took seconds flat and now reports U-Boot 2010.8.
 

This is important to anyone who has an NGW100 as this upgrades the ‘bootloader’ in the board to be able to read 2GB cards. The U-Boot bootloader that ships preloaded in the card won’t read the cards with large blocks. We’ve been stuck with older cards, usually 64 and 128 MB. Dave had one card that was 1GB with the small block setup. That’s the card we ended up using to load the flash image.

 

We had quite the group for the first Wednesday of the month. Remember there are several other groups that meet the first Wednesday of the month so the Technet and Tech Party are usually kind of light. We did great this week though!

Remember EVERYONE is invited to our group – you don’t have to be involved in any of our current projects to attend. The social value of this group is immeasurable! From time to time the group leader does focus the attention of the group to a specific point, but other than that this is definitely a multitasking group.
 

 
Let the knowledge flow

It is absolutely the best thing in the world to have a room full of Elmers an aspiring techs. Here is Jims VFO showing the large range of coverage he has, with Vern and Dave in the background digging in to their projects.
 
 
 

 
Here is a closer view of Jims setup and the frequency. Also note the power supply showing 80 mA current at 13.8v. Keep in mind the entire circuit is not powered, just the VFO and display.
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
See you next week!
Come out to next weeks Tech Party! Log in to the net on 147.120 Wednesday at 8pm if you can’t make it in person. There’s always something good going on and now n then there’s munchies! Never be afraid to bring munchies – you become an instant hero of the 147120 Tech Crew ;]

Last Wednesdays tech net was a raving success! Although there were only a handful of us there we finalized the defeat of our shortcomings with the Bitx20 VFO. What’s best, is that we used the tools that WE BUILT to test it! woo hoo!!
 

Verns VFO
is the first working properly. With the caps that Dave got from Mouser Electronics (Part # 23PW156; Film capacitors; styrene 50V 560pF) and the replacement variable cap, this puppy is dead on and unbelievably stable! The poor little am radio cap just wasn’t happy; it was shorted or possibly corroded, either way it was ‘jumpy’ every time we tried to do anything with it and we just couldn’t figure out the little trimmers on the back.
 
Replaced the Capacitor
The original was a little rusty or something

I had picked up a small ‘offcenter’ variable cap off ebay some time ago. The value is the same as the one in the kit so I was confident it would plug right in. I had built a small reduction on a 6:1 vernier giving a total of 30:1. Yup, it takes 15 turns of the knob to go from one end of the band to the other – 10 KHz per turn at the bottom end, and 20 KHz per turn at the top. Not bad!!

We used the FLL frequency counter kit we had built a couple months ago to test the VFO. It turned out to be a nice little tool for tuning the circuits in the BItx20. Verns ended up having a coverage of apx 3.998 to 4.352 – again very nice! Verns price for the reduction? He has to make the transceiver look really good ;]
 
The Perfect Setup?
Good enough for Nate!

The test was done on top of Nates neat setup he is building for his breadboard. He found a ‘briefcase’ type box at Skycraft and attached his breadboards on top of it, leaving room inside for all his accessories. In this test we used the power buses to make hookup much easier. Below is a view from another angle. Note the power supply showing the unit drawing 90 mA at 12v – backlight and all! Of course just the VFO and Frequency Counter are powered right now.

We really did have a lot of fun with this one. Vern had to rewind his toroid several times, finally finding a smaller diameter wire in order to put his final 54 turns on the core. It is spec’d at 50 turns, but it ended up being too high in frequency. When he tried to go over 50, it was not in a single layer winding with the wire provided to the inductance was way off. The final verdict – 54 turns with #32 wire on the core provided. Yay!

Vern really likes hot glue. Every time he wound a core he’d glue it down for testing. We finally convinced him to just glue the final result down. When dealing with things like this, like the inductor in an oscillator, physical stability is very important. Gluing the core down will keep it from moving and causing minute ‘microphonics.’ Good job Vern.
 

The Fine Tune Control gives almost a perfect 3 KHz shift – a little over 1.5 KHz each side of center. That’s extremely nice as all you have to do is tune ‘em in so you can hear ‘em with the main tune, and then adjust ‘em so you can understand ‘em with the fine tune. As designed and described!

So we were able to conquer the VFO – now on to the next stage. There are several builders going on to the audio stage next, a couple into the mixers. Next week we’ll discuss who is where and what new challenges we may face.
 
 
The Meeting Was A Smash
and we had a good time, too!

All in all we had a great tech experience, a great tech net, and a great result from the evening! I hope to see you next week at the tech party or at least check you in to the Wednesday Night Tech Net.

TECH ON!!

We have been having a difficulty with the VFO section of our BiTX20′s … I’m scratching my head and wondering why we’re off frequency but with the right spread. Enter Mario …

DUH, I never checked the values; we had discussed that there were no 560 PF NP0 caps in the kit, but I totally forgot. Mario asked, ‘where did you get the caps?’ Well, the builders had used the 56pf caps in the kit and it makes sense why none of them were on frequency.

We are making an order for 560 pf caps, but they will not be NP0. They will be very close, but we can’t find NP0 caps. It’s fine tho, the ones we are looking at have less than a decimal of a PF over a huge temperature range.

If you’d like to get in on that buy please contact Dave KC4ZVW or myself in the next few days and we’ll get you in on the pile.

I feel stupid, sorry I didn’t look at that, but at least we know where to get replacements.

Tracy N4LGH

This weeks Solder Social was a great learning experience!

Yeah, I’ve started calling our BiTX20 building group the Sewing Circle with Soldering Irons. A Soldering Circle! What’s the difference? A bunch of old bitties sitting ’round gossiping and trying to make ourselves sound important to one another. It’s a hoot!

We saw firsthand what a couple of picofarads can do to / for a filter. The BiTX20 transceiver front end has a nice bandpass filter that doubles as the front end filter for the receiver and the driver filter to the 5W PA. It’s a fairly important part of the circuit because if it’s not tuned well, performance will suffer on both receive and transmit.

First off, the documentation is a little contradictory to the markings on the board. In the photos of the board layout, the filter capacitors are marked 68pf. They are also 68pf in the supplied schematic. BUT, on the board itself, and in the written text, it calls for 33pf. In the text it states one could use either a 33 or 47 pf. We figured it was because of the tuning range of the inductors.

Some of us had already built the filter with 39 pf caps that appear to have been substituted for unavailable 33′s or 47′s. Maybe it was in the middle of the range?

Dave KC4ZVW had his Filter / Amp assembly ready first so we applied power and checked voltages per the instructions – everything was within tenths of volts, fantastic!

Next we went about setting up the Tracking Generator and Spectrum Analyzer. Thanks to Tom KD4WOV for helping us get that set up. I’ve never done that on a filter before.

Wow, what a mess! It had huge insertion loss and a lousy pattern. But after fiddling with the caps a bit Dave found a nice compromise between pattern and insertion loss.

Mario KU5E had used 33pf capacitors and came up with completely different results. He ended up removing the 33′s and putting in the 39′s. What a difference! We spent quite some time fiddling with the pattern and insertion loss with the 33′s and were never able to get less than 15dB of pure wasted signal.

As usual, Vern Ki4SDY was an excellent host and generously provided some caffeinated beverages, although I’m not sure this group really needed any stimulants ;]

Once I finally figured out how to take a picture of the spectrum analyzer screen these shots came out pretty well. Next week I’m going to bring my desktop tripod so that I don’t have so many blurry shots. These screens sure tell the story. We were able to get these tuned to with a dB or so insertion loss.

Overall the filter looks like it has better than 20 dB overall rejection, with less than 3dB insertion loss in about a 100 kHz passband. We don’t think we have this filter optimized – I will likely try several values there. Perhaps a variable?

Everyone is invited to our weekly Solder Social at Verns barber shop in Longwood, near the intersection of Ronald Regan Blvd and Church Street. Vern is the second door east on Church.

Hope to see you all there next week!

Last nights build meeting was great! We’re officially batting 1000 on the FLL kits! Jims took some rework on the solder connections to the chip socket, but we were all functional before we left.

We were amazed at the accuracy of these little buggers. One of the units was within 3 Hz at 10 MHz! We were able to accurately read frequencies up to 60 MHz. It was fairly sensitive from 20 MHz and down but we needed to pump up the output of the signal generator as we went up in frequency. But it was very accurate right up to the point where it couldn’t lock any longer.

Cool!!

The next part of the build is the bandpass filter and amplifier for the receiver. Some of us have elected to start on the Power Supply section of the PA so that we have a source of 12v for testing. Since there are provisions on the PA board for ac operation most of us are taking advantage of that.

Anyone is welcome at the build party! We have a couple extra ‘seats’ and truly enjoy sharing at this meeting. I would have to say we’ve had the most pleasant and productive build sessions I’ve been to in decades.

Each week we share sources of parts, play ‘show n tell’ with ‘stuff’ we’ve acquired, and generally just chat away in between questions comments and statements about the project. We discuss the circuit, the nuances of the mechanical construction and even ponder programming code.

All in all, it’s a great meeting and I can’t wait ’till the next one. See you all then!!

Tracy N4LGH

Well, the BiTX Builder Group is moving along just fine! Most in the group have identified the parts inventory, some have begun soldering the FLL kit.

Tonight we discovered how important a good soldering iron is. We also discovered several unique ways to put together this little project!

We decided at the onset of this project that the Frequency Counter portion of the FLL (Frequency Locked Loop) would be where we start with this project. That leaves us with a nice little piece of test equipment to use on the other parts of the project. Nice!

We discovered that all the kits were short one 10K resistor in the FLL parts pile. We also discovered that the header supplied to go on the FLL board does not fit.

Patrick discovered one can simply solder the header on the LCD instead of the FLL board and put the wires directly on the FLL. (It was intended to go the other way around …) I decided to do away with the header and connector altogether.

Here are a couple of pictures of my Frequency Counter. It powers up, but I haven’t tried to get it to display a frequency yet.

I had been saving the clipped leads of the Capacitors and it dawned on me that they would cumulatively have quite a bit of sturdiness even though each in its own was easily bent. It turned out much nicer than I thought.

It’s time to go ahead and see if this thing is able to count a frequency! Then I need to settle in on how to mount it into my RCA CB Co-Pilot chassis I recently gutted.

So much fun – I’ll report more as I progress!

Tracy N4LGH

..

Well, I’ve been working on linear dials for radios for a long time and just haven’t been able to finalize it until just recently.

I realized that the Tamaya gears I had obtained from Colonial Photo and Hobby would screw right on the front of the variable capacitor in the BiTX20. It didn’t take me long to dig out my Universal Plates and pulley hardware and come up with the nifty item pictured below.

I’ll make a post to the Wiki in a few weeks with detailed steps on how I go about actually setting the thing up to work with a real radio. Right now this is a prototype and I don’t know exactly how I’m going to go about the final layout. The marvelous thing about gears is they can be physically laid out just about any way necessary as long as the sequence is correct.

The end result will be a 2 or 3 inch cube that can be mounted behind the front panel with the dial pulleys mounted to the panel as well. I have started to lay out a brass tube runner for the dial pointer which will be very small brass rods (almost wire) soldered onto the brass runner.

It is a 72:1 ratio giving 36 turns to cover the 350 kHz wide 20 meter band. This theoretically exceeds my 10kHz per turn requirement but realistically this is not a ‘frequency linear’ capacitor so it will be very wide at one end and very tight at the other. My luck the tight end will be the upper end. Still, with 72:1 ratio it will have a very smooth tune even at the tightest part of the band.

The feel is decent, the action overall smooth for the course gears I used. The only backlash in the system is introduced by the rubber band type belt I put on for the test. I will get some real dial string and a spring to load the pulleys and it should be smooth as silk. With a flywheel on the other end of the knob shaft it should have a nice ‘spin’ to it!

The only problem it has right now is the gear ratio is very strong and will twist the screw right out of the capacitor without you even feeling it. Once I have the runner made I’ll put stops at each end and there won’t be any problems with the gears unscrewing from the cap.

I chose these parts because they can be obtained at any hobby store and over the internet, as are the pulleys, rods, and universal plates.

I have purchased a lot of gears over the past months but to estimate I think one would have about $15 – $20 in this. If several were to pool and get the larger bags of the gears and rods and would be about $10 – $15 each to make as a group buy.

I have a large gear set up to take the 1/4″ shaft of a regular tuning capacitor. With the strength this thing has, there’s no doubt it will turn it as well.

Dig in!
Tracy N4LGH

Meeting #1

This was held on 30th of Nov 2009.

Talked about tools needed to assemble the project, soldering and the assembly instuctions that we are going to use.

I mentioned that the discussion list was on YahooGroups which can be found from here.

---

---

Other pictures

73,

David — KC4ZVW

Resources abound on the Internet. The G-QRP Club located in England is one that I enjoy. If you “click” on their logo above it will take you to the site. They have data sheets with excellent  information for the beginner to the advanced builder. The Club magazine, SPRAT, is published quarterly and is full of inspiration. I just received the fall edition and found an article on Weak Signal Propagation Reporting, WSPR for short. There are plans for The SixBox, a very simple 6m AM transceiver. The G-QRP Club is devoted to low power communication. Membership is $15 a year and you will receive four issues of SPRAT.  73

Robin

As Radio Amateurs who like to build, anything that we come across could be inspiration for a project or upgrade. I was Elmered into the hobby by  Dave Carter, KA1HDG, during a one week class at Great Lakes Adventist Academy. GLAA is an ARRL “The Big Project” School. With part of their funding they set up a satellite station… the inspiration.

This is the top of my satellite station. I made a 100 point field day contact with AO51 at 10 degrees over the horizon. My first soldered component of my first kit was inspired by that satellite station at GLAA. Needing computer control of the AZ/EL rotors I purchased the PIC16F688 Satellite Tracker Interface: ST1 from FOX DELTA. I wanted USB control so that required soldering a small FT232R chip.

This chip was the first thing I put on a board. I figured that if it didn’t work, why solder the rest.

If I can solder a chip anyone can. Heat up the iron and follow your inspiration. 73

Robin