Jims Coverage

Jim used a larger value variable capacitor, so his VFO has more frequency coverage ...

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.

This is the disk!

This is the SD 'disk' that we used to update the Flash (U-Boot) on the NGW100. It's an older card that the older U-Boot could handle.

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.

Vern, Ralph and Roy

Vern, Ralph and Roy doing what we do at the Tech Party!


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.

Jim, Nate and Bert

Jim, Nate and Bert working on Jims VFO - conquored for the most part, it's on frequency but covers more than the 20 meter band because he used a larger variable capacitor. What we need to do next is calculate the new capacitors to set his bandwidth.

Ejhngofarten nkne hbgrlop

Roy and hbgrlop being entertained by some of the technical magic that happens at every Tech party!

Jims VFO

Jims VFO with Vern and Dave in the back

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.

Jims VFO

Here's Nate working on Jims VFO. Note the neat setup Nate made with some protoboards and a neat 'laptop' type case he found at Skycraft. This week his creation sported individual switches for each of the power busses, 12, 5 and 3.3v regulators and a lot of spirit for the next run of mods!

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!!

lower frequency

Lower Frequency

Upper Frequency

Upper Frequency

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

nice open air capacitor

reduction and variable capacitor

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!

In Operation

In Operation

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.

The Setup

The Tech Party BItx20 Setup!

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!

hot glue

Fastening the toroid with Hot Glue. Once on, simply press the core against the board before the glue sets and this little circuit is good n' stable!

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.

Fine Tune arrangement

Fine Tune Control

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.


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