Topics

PCB uBitx -working on it-

VK3HN
 

Modular boards!  Brilliant!  I never build a receiver, transmitter or txcvr all on one board, as I inevitably end up changing parts or stages of the design.  I always build RF, filters, PA, IF and BFO, and VFO/DDS on separate boards, usually screened and boxed, to provide physical separation, individual debugging and potential rebuilding/replacement, repair, reconfiguration, etc.  The modular boards are the right approach for an early stage design.  I'm working on a scratch build of uBitx and will post pictures and descriptions as the modules come alive. Regards Paul VK3HN.   

Jerry Gaffke
 

That part about the image problem on the Bitx40 wasn't written very well.

Assume we are tuning into 7.25mhz with a stock Bitx40.  The Raduino VFO will be at 12-7.25=4.75 mhz.  The 4'th harmonic of the VFO is at 4*4.75=19mhz, so has an image at 19-12 = 7.0 mhz on both transmit and receive.   The best solution is to hack the Raduino sketch for a high side VFO at 12+7.25=19.25mhz, harmonics of the VFO will be much higher frequencies and pretty much out of our hair  However, you will have to adjust the BFO frequency down by 3khz or so to move back to lower sideband operation, as with a high side VFO you get upper sideband operation.  

On Sun, Mar 12, 2017 at 10:43 am, Jerry Gaffke wrote:

There is a possible problem with transmitting images on the current Bitx from a 4x harmonic of the VFO at 19mhz, as that's a signal that fits through all the filters, easy to fix by going to a high side 19mhz VFO.

 

Jerry Gaffke
 

I agree, I doubt we will be transmitting any images into the aircraft band.  There is a possible problem with transmitting images on the current Bitx from a 4x harmonic of the VFO at 19mhz, as that's a signal that fits through all the filters, easy to fix by going to a high side 19mhz VFO.  On the uBitx, could continue with the current design with optional shielding, fall back to a 35mhz IF and 15 meter max as per my previous post if there are issues.  

On Sun, Mar 12, 2017 at 10:11 am, Ashhar Farhan wrote:

As opposed to airCraft traansceivers that are 25 watts.

 

Ashhar Farhan
 

The fm broadcasts are often powered by transmitters of 10kw or more. As opposed to airCraft traansceivers that are 25 watts. The breakthrough of FM bc qrm will be quite hard to put down as it is pretty broadband. It might make sense to use 55mhz if. The images will be from 110 mhz onwards.
- f

On 12 Mar 2017 10:23 p.m., "Jerry Gaffke via Groups.Io" <jgaffke=yahoo.com@groups.io> wrote:

Perhaps the standard build has a 35mhz first IF, max operating frequency of 21.45mhz.  So 15 meters works though may not be optimal:  At 21mhz, the VFO would be at 21+35=56mhz, an image at 91mhz would have a mixer product at 91-56=35mhz and thus sneak through that first IF filter.   Also, 21mhz is getting close to 35mhz.  Any bands below 15 meters should work great.  Include notes on how to modify for a 45mhz IF and add shielding from copper pipe scraps for operation up to 30mhz as per the original uBitx design.

Jerry, KE7ER

On Sun, Mar 12, 2017 at 12:42 am, John Backo wrote:

Perhaps a 60-90 MHz image would be better?

 

Jerry Gaffke
 

Perhaps the standard build has a 35mhz first IF, max operating frequency of 21.45mhz.  So 15 meters works though may not be optimal:  At 21mhz, the VFO would be at 21+35=56mhz, an image at 91mhz would have a mixer product at 91-56=35mhz and thus sneak through that first IF filter.   Also, 21mhz is getting close to 35mhz.  Any bands below 15 meters should work great.  Include notes on how to modify for a 45mhz IF and add shielding from copper pipe scraps for operation up to 30mhz as per the original uBitx design.

Jerry, KE7ER

On Sun, Mar 12, 2017 at 12:42 am, John Backo wrote:

Perhaps a 60-90 MHz image would be better?

 

Henning Weddig
 

This means that the low pass filter has to be put into a "watertight" box with inner sections to seperate the individual stages. Even then make sure that the self resonances of coils and caps are far away from the image and posssible furtehr images.

Henning

DK5LV


Am 12.03.2017 um 16:21 schrieb Ion Petroianu:

It might be an issue if low pass filter is not well made. If the low pass filter works as designed it will attenuate more than 100 dB at 90MHz.

On top the RF PA does not work at those frequencies, so I would not worry too much.
--
Ion

VA3NOI


Rahul Srivastava
 

Hi!

I am thinking something modular on these lines... Modules are self explanatery..

73

Rahul VU3WJM


On Saturday, 11 March 2017 7:30 AM, Juan Carlos Berberena Glez <cubanqrp@...> wrote:


Hi Guys, here something my friend Heriberto-CM2KMK- is doing for the uBitx
Have a good week end
rv's

73's Jc


Ion Petroianu, VA3NOI
 

It might be an issue if low pass filter is not well made. If the low pass filter works as designed it will attenuate more than 100 dB at 90MHz.

On top the RF PA does not work at those frequencies, so I would not worry too much.
--
Ion

VA3NOI

MVS Sarma
 

Any audio amp could be tried but it should be generally available in spares market. Perhaps for a design, better to use dip8  or soic8.

This is NOT a reply for Ashhar Farhan's design. M1  and M2 are to be shorted by relay contact 3&5 of K3 as per original design.

 If the  PCB implementer wanted to keep out the Linear PA ha may have to bring out that contact back to  exciter board , if I may call it so.
Sarma
 vu3zmv

On Sun, Mar 12, 2017 at 2:12 PM, John Backo via Groups.Io <iam74@...> wrote:
"the image of first LO+IF will float from 90 to 120 mhz. This is bang inside thr FM broadcast band."

Not only that, but it could possibly interfere with the aviation communication band.
That is a definite no-no in any part of the world. Perhaps a 60-90 MHz image would be better?
Or mandatory heavy shielding.

In researching the TDA2822, I note that there are two versions. One, a 16 pin dip is obsolete.
The current one is a 8 pin dip unit. They have different pinouts and are not interchangeable.

In studying the board, there seem to be several differences between the schematic and the layout.

There is an extra transistor in the AVC interface system. It is used where M1 and M2 are
supposedly connected to the relay. (??)

There is only one relay on the board.

It appears that there is no output to the 2N2219's and final transistors; both transformers are shown
as bifilar whereas one is trifilar and is the output interface.

More works is needed to make this a viable board. Looks nice though.

The suggestion to make modules and interconnect them is probably the way
to go right now.

john
AD5YE






--
Regards
Sarma
 

John Backo
 

"the image of first LO+IF will float from 90 to 120 mhz. This is bang inside thr FM broadcast band."

Not only that, but it could possibly interfere with the aviation communication band.
That is a definite no-no in any part of the world. Perhaps a 60-90 MHz image would be better?
Or mandatory heavy shielding.

In researching the TDA2822, I note that there are two versions. One, a 16 pin dip is obsolete.
The current one is a 8 pin dip unit. They have different pinouts and are not interchangeable.

In studying the board, there seem to be several differences between the schematic and the layout.

There is an extra transistor in the AVC interface system. It is used where M1 and M2 are
supposedly connected to the relay. (??)

There is only one relay on the board.

It appears that there is no output to the 2N2219's and final transistors; both transformers are shown
as bifilar whereas one is trifilar and is the output interface.

More works is needed to make this a viable board. Looks nice though.

The suggestion to make modules and interconnect them is probably the way
to go right now.

john
AD5YE

Jerry Gaffke
 

A couple possible solutions if this does look like trouble:  Include a scheme to add shielding at the front end for those that need it.  Or go to a higher freq using the muRata PX1002 86.85mhz SAW filter, $5USD at quantity.  Both mentioned in post https://groups.io/g/BITX20/message/22972


On Sat, Mar 11, 2017 at 08:08 pm, Ashhar Farhan wrote:

He points out that the image of first LO+IF will float from 90 to 120 mhz.

 

Ashhar Farhan
 

Gang,
I received an email about the ubitx from wes. He points out that the image of first LO+IF will float from 90 to 120 mhz. This is bang inside thr FM broadcast band. It could lead to some spurs.
Is anyone scratch building this righway? Id like to get some real world testing done before we press the GO button for the rest.
- f

On 12 Mar 2017 6:59 a.m., "Rahul Srivastava via Groups.Io" <vu3wjm=yahoo.com@groups.io> wrote:
Hi!

You just snatched the words from my mouth, it will be great in true experimeter's spirit...

73

Rahul VU3WJM


On Sunday, 12 March 2017 6:40 AM, Ion Petroianu <ion.petroianu@...> wrote:


This is very nice for a final product but for experimenting wouldn't be better to have small blocks we can interconnect. From what I see we are working with 50 Ohms input and output impedance so short runs of RG 174 will provide links between modules.
Also when experimenting is more cost effective to use the special price for prototype boards (10 boards, 10X10 cm, for $10)
If the layout is squeezed you can get 2 or three layouts on one 10X10 cm board.
What do you think about the idea. Shall we start splitting the schematic in blocks?
--
Ion
VA3NOI


Rahul Srivastava
 

Hi!

You just snatched the words from my mouth, it will be great in true experimeter's spirit...

73

Rahul VU3WJM


On Sunday, 12 March 2017 6:40 AM, Ion Petroianu <ion.petroianu@...> wrote:


This is very nice for a final product but for experimenting wouldn't be better to have small blocks we can interconnect. From what I see we are working with 50 Ohms input and output impedance so short runs of RG 174 will provide links between modules.
Also when experimenting is more cost effective to use the special price for prototype boards (10 boards, 10X10 cm, for $10)
If the layout is squeezed you can get 2 or three layouts on one 10X10 cm board.
What do you think about the idea. Shall we start splitting the schematic in blocks?
--
Ion
VA3NOI


Ion Petroianu, VA3NOI
 

This is very nice for a final product but for experimenting wouldn't be better to have small blocks we can interconnect. From what I see we are working with 50 Ohms input and output impedance so short runs of RG 174 will provide links between modules.

Also when experimenting is more cost effective to use the special price for prototype boards (10 boards, 10X10 cm, for $10)

If the layout is squeezed you can get 2 or three layouts on one 10X10 cm board.

What do you think about the idea. Shall we start splitting the schematic in blocks?
--
Ion

VA3NOI

Rahul Srivastava
 

Hi!

Great looking PCB. Single sided board will go a long way in making it popular and easy to assemble. I guess the PCB is being done in Sprint layout, how about posting the .Lay file so that we all can contribute to it...

73

Rahul VU3WJM


On Sunday, 12 March 2017 4:26 AM, Lawrence Galea <9h1avlaw@...> wrote:


Would be nice to share i with the group on PDF
Regards
HAGWE
Lawrence

On Sat, Mar 11, 2017 at 2:59 AM, Juan Carlos Berberena Glez <cubanqrp@...> wrote:
Hi Guys, here something my friend Heriberto-CM2KMK- is doing for the uBitx
Have a good week end
rv's

73's Jc



Lawrence Galea
 

Would be nice to share i with the group on PDF
Regards
HAGWE
Lawrence

On Sat, Mar 11, 2017 at 2:59 AM, Juan Carlos Berberena Glez <cubanqrp@...> wrote:

Hi Guys, here something my friend Heriberto-CM2KMK- is doing for the uBitx

Have a good week end

rv's


73's Jc


Jim Smith <zx97lite@...>
 

Awesome,and thru hole too!

Pete  WB9FLW

Richard Andrew Knack
 

It would be great if the files could be posted, when finished, in both Eagle format and as a direct image that could be laser printed and toner-transferred. Looking good!

Rich
KC8MWG


On Saturday, March 11, 2017 12:56 AM, John VA7JBE via Groups.Io <va7jbe@...> wrote:


No reason that there couldn't be two versions of the PCB, one for SMD and one for through hole.


John VA7JBE
 

No reason that there couldn't be two versions of the PCB, one for SMD and one for through hole.

Yeonghwan Jun
 

I expect It will be good product.
because I want to have it more quickly.

Thanks for it.