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PCB uBitx -working on it-

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

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


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


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?

 

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
 

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.

 

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.

 

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.