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.

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

On Wednesday at about 8:00 pm local time is the 147.120 Tech Net.
You can find the Tech Net on the 147.120 MHz repeater (KJ4PLD) with a CTCSS tone of 103.5

the 147.120 Tech Net "net-operator"

Tracy (N4LGH) running the Tech Net

Here Tracy (N4LGH) acting as the Net Op at Vern’s Barber shop.

Trying to figure things out by experimentation can be very difficult, especially when you’re not sure what you’re looking for or dealing with. There are many unknowns in most experiments and we need a way to control the experiment as much as possible to isolate the data you’re looking for.

The Scientific Method is a way of looking at a problem and following a controlled set of steps to solve it. Keeping all known elements constant makes it easier to isolate or identify the unknowns.

Join us this week for a discussion on The Scientific Method. Do a little research on the subject (Google ‘the scientific research’ with or without the quote) and be prepared to engage in a discussion that is sure to enlighten your tech abilities!

See you all Wednesday evening at 8pm on the 147.120!
Tracy N4LGH

Hello Tech Fans!

This coming Wednesday we will be discussing Test and Measurement Equipment – what it is, how to use it, and hopefully personal experiences of our participants. This should be a fantastic conversation about testing and measuring all things ham radio.

See you Wednesday at 8!
Tracy N4LGH

This weeks Technet will be hosted by Phil, AI4OF. Phil is an extremely knowledgeable individual that has a way of explaining things simply and usually with good examples.

I have a one-time financial opportunity that I cannot refuse … I guess we all have a price? hihi we’re all plagued with having to pay the bills ;]

Make it a great turnout for Phil and thank him for filling in last minute!

Thanks Phil!
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?

Contemplating the filter

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.

At last, a decent pattern with low 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 ;]

Best we could get with the 33pf caps!

Now this is a good pattern!

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?

a higher resolution shot of the pattern

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

I want to apologize to everyone who expected a Tech Net tonight. I had a series of personal incidents that prevented me from getting on the air tonight. I’m just now getting in and still, I have no antenna!!

This WILL be solved before next weeks net!

I WILL be at the build meeting tomorrow!

Thanks for your patience,

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.

my FLL (up side down)

my FLL (up side down)

Looking from the back

Looking from the back

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.

Top view showing rigid wiring

Top view showing rigid wiring

Alive! (need to clean the lense ...)

Alive! (need to clean the lense ...)

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

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