Re: Sad reality of stock vfo
It is a complete, finished radio for $45!! Of course it is a compromise, and you have always been frank about the design issues.?
I am not complaining. I had fun putting this together, and I¡¯m learning more from this one project than several years of other experiences. Just understanding the costs and compromises of the design decisions, and their effect on the final performance, has been a great lesson, and it is ongoing.
I will continue to explore, first the limits of changes to the analog vfo onboard, and then possible learn to build an outboard vfo.
I also look forward to the opportunity presented by the DDS VFO and learning about the Arduino architecture.
I find it hard to imagine a better way to spend $45 or $59 for an education.
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I will be frank. This design is a compromise. The VFO should have been on a separate board. I thought about it for a pretty long time. There was no cost difference. There was just one more board to hookup and wire up. In the end and after countless conversations with some co-builders, I decided to include the VCO on-board. I am still convinced that this was a better option than an outboard VFO for easy of use.
Here are some notes from my experimentation.
1. It is NOT about the capacitors. I build a two-tone oscillators using these caps that run at 14.000 and 14.200 MHz directly. They are so solid, I can't believe that it is a free running oscillator. 2. The culprit is heat. The RF amplifiers have significant current, there are three of them. The heat dissipates through the ground plane and heats up the VFO components. This heat would be missing if we used through hole components as those components are off the board. 3. The heat sensitivity is also due to it being a VCO. The varactor tuning couldn't be avoided as getting good quality capacitors is very tough these days.
If you'd still like to retain the analog tuning, do what bill suggests. Build an outboard VFO, shield it well and it will be rock stable.
- f
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Re: Sad reality of stock vfo
NP0 capacitors for C94 95 96 WILL tackle the heat problem Farhan!
Happy new year!
Raj
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2. The culprit is heat. The RF amplifiers have significant current, there are three of them. The heat dissipates through the ground plane and heats up the VFO components. This heat would be missing if we used through hole components as those components are off the board.
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Re: Sad reality of stock vfo
I will be frank. This design is a compromise. The VFO should have been on a separate board. I thought about it for a pretty long time. There was no cost difference. There was just one more board to hookup and wire up. In the end and after countless conversations with some co-builders, I decided to include the VCO on-board. I am still convinced that this was a better option than an outboard VFO for easy of use.
Here are some notes from my experimentation.
1. It is NOT about the capacitors. I build a two-tone oscillators using these caps that run at 14.000 and 14.200 MHz directly. They are so solid, I can't believe that it is a free running oscillator. 2. The culprit is heat. The RF amplifiers have significant current, there are three of them. The heat dissipates through the ground plane and heats up the VFO components. This heat would be missing if we used through hole components as those components are off the board. 3. The heat sensitivity is also due to it being a VCO. The varactor tuning couldn't be avoided as getting good quality capacitors is very tough these days.
If you'd still like to retain the analog tuning, do what bill suggests. Build an outboard VFO, shield it well and it will be rock stable.
- f
On Sun, Jan 1, 2017 at 9:44 AM, Thomas Noel tnoel@... [BITX20] <BITX20@...> wrote:
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John,
As I said - I knew from others¡¯ experience that the stock design has some significant limitations. I just had no previous personal experience with such builds. I have read of quite a few design mods that offer improvement. The design is simple and easy to mod as Farhan intended. I built the stock design as a starting place for learning.?
I was surprised to see the drift so severe that it is hard to hold frequency during an ¡°over¡±. I have made more than a dozen QSOs in less than two hours of operation. The operator on the other end even commented that I was drifting off frequency.
I would like to continue to experiment with the all-analog radio before moving to the DDS VFO.
Where exactly would you start? Replace the resistors as suggested by Farhan? They were included with my purchase. Which capacitors would you replace to stabilize the VFO, and change just the type, or change any of the values? My tuning range is just where I would want it now.
If anyone can give me a step-by-step attack plan in order of best anticipated return on effort, I would appreciate it a lot.
Thomas, That's not optimal behavior for that sort of design. It can do much better than that. I think you should revisit the traditional solutions for such problems and them implement them before moving on- NPO and styrene capacitors might be a start.
John KC9OJV
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Re: It stopped transmitting
Hi Kent,
Firmware version s1.02c is perfect! It is the latest version. In this version there was a change to eliminate audible clicks when the frequency changed.
I don't own a BITX40. On the QRP Labs VFO kit page there are a few connection details that were provided by Ashhar Farhan when he recommended the QRP Labs VFO kit for use with the BITX40. That's all I know!
73 Hans G0UPL? ?
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Re: Sad reality of stock vfo
John,
As I said - I knew from others¡¯ experience that the stock design has some significant limitations. I just had no previous personal experience with such builds. I have read of quite a few design mods that offer improvement. The design is simple and easy to mod as Farhan intended. I built the stock design as a starting place for learning.?
I was surprised to see the drift so severe that it is hard to hold frequency during an ¡°over¡±. I have made more than a dozen QSOs in less than two hours of operation. The operator on the other end even commented that I was drifting off frequency.
I would like to continue to experiment with the all-analog radio before moving to the DDS VFO.
Where exactly would you start? Replace the resistors as suggested by Farhan? They were included with my purchase. Which capacitors would you replace to stabilize the VFO, and change just the type, or change any of the values? My tuning range is just where I would want it now.
If anyone can give me a step-by-step attack plan in order of best anticipated return on effort, I would appreciate it a lot.
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Thomas, That's not optimal behavior for that sort of design. It can do much better than that. I think you should revisit the traditional solutions for such problems and them implement them before moving on- NPO and styrene capacitors might be a start.
John KC9OJV
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Re: Sad reality of stock vfo
I can relate to this, and it's why I am switching to a digital VFO. Gluing down L4 was a *huge* improvement for my BITX40. The other thing is to have it in an enclosure that isn't drafty, so that the temperature stays roughly the same if possible. I'm still waiting for the VFO from QRP Labs to get here, but contacts ARE possible with the stock VFO. KC9OJV's suggestion is also a very good one, and were I not going digital, I'd be doing that next.
Ryan? KC7RYS
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Re: Sad reality of stock vfo
Thomas, That's not optimal behavior for that sort of design. It can do much better than that. I think you should revisit the traditional solutions for such problems and them implement them before moving on- NPO and styrene capacitors might be a start.
John KC9OJV
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I knowingly and with full understanding of the expected consequences built out my Bitx40 fully stock. Analog VFO, original resistors etc. All alignment went just as described in manual, and everything works just as advertised. The receiver is quite sensitive, and even without AGC it is easy to operate weak and strong stations. I have about 220kc of tuning range from 7.070 to 7.290.
The challenge is the VFO drift - even though I leave the set on all the time with volume turned down to silent, the drift is so severe that I must re-tune at least every 10-15 seconds during an attempted QSO or I drift so far off frequency that when I un-key - the other station is often gone, moved out of my passband. Never dreamed the drift would be this bad.
I have the replacement resistors for the VFO, and that will be next. I may try some of the other suggested changes just to further my own learning experience with this simple and elegant design.
But I have also ordered the DDS VFO parts!
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That's very philosophical and I like it! :-))
On Dec 31, 2016 7:20 PM, "ron van doremalen ronvandoremalen@... [BITX20]" < BITX20@...> wrote:
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When shipped it will come
Sent from my iPhone
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I ordered mine on the 25th. Payment shows up in PayPal, but no tracking info.
Rich
KC8MWG
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Yep, tried aftership as well, no info.
73
Don Frasher AD7LL
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When shipped it will come
Sent from my iPhone
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I ordered mine on the 25th. Payment shows up in PayPal, but no tracking info.
Rich
KC8MWG
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Yep, tried aftership as well, no info.
73
Don Frasher AD7LL
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I ordered mine on the 25th. Payment shows up in PayPal, but no tracking info.
Rich KC8MWG
On Saturday, December 31, 2016 7:57 PM, "AD7LL donfrasher@... [BITX20]" <BITX20@...> wrote:
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Yep, tried aftership as well, no info.
73 Don Frasher AD7LL
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Ashhar, do the new ones use 70ma in recieve instead of 90ma because you have switched from100 to 220 resistors? Jerry aa1of
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Yep, tried aftership as well, no info.
73 Don Frasher AD7LL
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My experience was the same as most - I got initial tracking info from IndiaPost, but never heard again until it was on my doorstep.
Have Faith!
Tom kf7rsf
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I placed my order on 12-23, and I did get a tracking # via paypal. ?However, even if I enter it directly at Indiapost, google , or elswhere, I get no info received. ? ?Has anyone else had better luck?? ?or have they not actually shipped them yet?
73 Don Frasher AD7LL
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Aftership? Sometimes search again delivers an update
Sent from my iPhone
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I placed my order on 12-23, and I did get a tracking # via paypal. ?However, even if I enter it directly at Indiapost, google , or elswhere, I get no info received.
? ?Has anyone else had better luck?? ?or have they not actually shipped them yet?
73
Don Frasher AD7LL
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I ordered and paid for just the Raduino on 12/23 and haven't heard anything either, so I'm guessing we just wait. Joel? KB6QVI
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On Dec 31, 2016, at 4:19 PM, donfrasher@... [BITX20] < BITX20@...> wrote:
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I placed my order on 12-23, and I did get a tracking # via paypal. ?However, even if I enter it directly at Indiapost, google , or elswhere, I get no info received. ? ?Has anyone else had better luck?? ?or have they not actually shipped them yet?
73 Don Frasher AD7LL
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I placed my order on 12-23, and I did get a tracking # via paypal. ?However, even if I enter it directly at Indiapost, google , or elswhere, I get no info received. ? ?Has anyone else had better luck?? ?or have they not actually shipped them yet?
73 Don Frasher AD7LL
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Dynamic Mic or Electret Mic in a Bitx40
I have a functional Dynamic Mic from an old CB Radio which would be very easy to use by removing the R121 Mic Bias Resistor from the Bitx40. ?It is my understanding that electret (condenser) mic's are more sensitive, and that replacing the dynamic capsule in the microphone is fairly straightforward.
Is there any reason not to install the electret element, or do dynamic microphones have any advantages over the electret?
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Craig
When you sign up for Yahoo groups you are presented with options for handling messages, replies, etc.
Arv
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On Sat, Dec 31, 2016 at 9:21 AM, 'Craig Kinsman' craig@... [BITX20] <BITX20@...> wrote:
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Hi
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I want to be a member of the group but dont want emails into my mailbox.
How do I do that?
?
Craig
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Re: 50 Turns on L4 VFO Inductor?
Mark
Adding more capacitance may help but this narrows the tuning range.? An interesting alternative might
be to glue two T37-6 cores together and wind your VFO inductor on those.? The turns needed will be
a little over half what would be necessary for a single core.? This is a possible solution that seems to
have been mostly ignored by builders and experimenters.
Arv? K7HKL
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On Sat, Dec 31, 2016 at 12:59 AM, Mark Baldridge marktbaldridge@... [BITX20] <BITX20@...> wrote:
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Greetings all,
I have been building the through-hole BITX20 v3B from Sunil Lakhani. After a good bit of trouble shooting, and a frustratingly illusive shorted solder joint, I was finally able to hear a signal from my signal generator all the way thorough the receiver!
The problem I'm experiencing however, is that I was unable to fit 50 turns of #35 wire on an FT37-6.
I think I finally had 39 turns before I ran out of space. And they're tightly packed! Thus my VFO runs at about 5MHz rather than in the 4MHz range.
Do you know of any solution for this? Is it okay to have multiple layers of windings on the core?
Thank you all!
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Raj vu2zap
Joel Caulkins/N6ALT
Tom Clifton