Topics

Rx while transmitting #ubitx


edoardo marchetti
 

Hello everybody,
This is the first time I check the transmission mode. Power output is ok, no emission in ssb without modulation but if I speak to the mike I ear my voice on the headphones. 
What could be the problem? I ear relay switching and also changing lcd writings
Thanks for reading
IU6DBK


Evan Hand
 

Does the feedback happen when connected to a dummy load?

73
Evan
AC9TU


edoardo marchetti
 

I have no dummy load... I know, I should make our buy one.
Thanks for answering my question
IU6DBK


On Sun, 18 Oct 2020, 22:54 Evan Hand, <elhandjr@...> wrote:
Does the feedback happen when connected to a dummy load?

73
Evan
AC9TU


Evan Hand
 

On Sun, Oct 18, 2020 at 04:01 PM, edoardo marchetti wrote:
I have no dummy load... I know, I should make our buy one.
Edoardo,
4 3watt 200ohm metal film resistors connected in parallel and a connector are all that you need.  That, or as I had 4 47ohm resistors and a connector I made one with two sets of 2 parallel resistors connected in series to equal 47ohm (close enough).

I had similar issues with my first build.  My 40meter off-center fed dipole was the issue.   I was able to reduce the RF getting back into the rig with 4 snap-on ferrites.  You could also try an "ugly choke" (ten or so turns of the coax before the shack- look it up on the internet), or some other way to reduce the RF on the coax shield getting into the shack.

There are two inexpensive dummy load kits available.  One is from QRP-Labs, the other from QRP Guys $8.50 and $10 US respectively.

Another question, which version of uBITX do you have, and what is the antenna?

73
Evan
AC9TU


Bob Lunsford
 

When I built the Heathkit QRP radios, they provided four 200 Ohm, 2W resistors that were paralleled for a dummy load. These were mounted on a connector that was attached to the radios' output connector.

Cheap enough. Even a very short piece of coax with a  connector already on it can be used by soldering the four resistors in parallel across the open end. No need to get fancy.

I still have the dummy load and if used only for a second or two, my 100W rig can be used and the dummy load gets warm...enough to touch with no problem.

On Sunday, October 18, 2020, 5:01:15 PM EDT, edoardo marchetti <mentorade@...> wrote:


I have no dummy load... I know, I should make our buy one.
Thanks for answering my question
IU6DBK

On Sun, 18 Oct 2020, 22:54 Evan Hand, <elhandjr@...> wrote:
Does the feedback happen when connected to a dummy load?

73
Evan
AC9TU


edoardo marchetti
 

Nice, so I have many options to decide!
Well, if you all are thinking radio frequency interference to be the cause of my issue, maybe is because audio cable and antenna cable are mounted in parallel to each other so, even if they are centimeters distanced, I should substitute the original antenna cable, made of two wires, with a coaxial.
I must try.
Thanks everybody!
73
IU6DBK

On Mon, 19 Oct 2020, 00:12 Bob Lunsford via groups.io, <nocrud222=yahoo.com@groups.io> wrote:
When I built the Heathkit QRP radios, they provided four 200 Ohm, 2W resistors that were paralleled for a dummy load. These were mounted on a connector that was attached to the radios' output connector.

Cheap enough. Even a very short piece of coax with a  connector already on it can be used by soldering the four resistors in parallel across the open end. No need to get fancy.

I still have the dummy load and if used only for a second or two, my 100W rig can be used and the dummy load gets warm...enough to touch with no problem.

On Sunday, October 18, 2020, 5:01:15 PM EDT, edoardo marchetti <mentorade@...> wrote:


I have no dummy load... I know, I should make our buy one.
Thanks for answering my question
IU6DBK

On Sun, 18 Oct 2020, 22:54 Evan Hand, <elhandjr@...> wrote:
Does the feedback happen when connected to a dummy load?

73
Evan
AC9TU


Rubens Kamimura
 

Hi
I would like help from you, I changed the box of my uBITX v4, now I am listening on the speaker while transmitting FT8, this did not happen before. Would anyone have any information?
73's de Rubens py2pvb.


Em dom., 18 de out. de 2020 às 17:50, edoardo marchetti <mentorade@...> escreveu:

Hello everybody,
This is the first time I check the transmission mode. Power output is ok, no emission in ssb without modulation but if I speak to the mike I ear my voice on the headphones. 
What could be the problem? I ear relay switching and also changing lcd writings
Thanks for reading
IU6DBK


Evan Hand
 

Rubens,
I would check the audio wiring.  When you changed boxes, did you add an audio amplifier?  If so, see if you can shield the wiring or use a snap-on ferrite to reduce the RF getting into the audio amp.  I suspect that is your issue.

More details including pictures heps us with diagnosing your issue.  By details, I mean any changes in modules or added circuit boards.  Also the new box information; was it a kit like one from AmateurRadioKits?

73
Evan
AC9tu


Rubens Kamimura
 

Evan

Photos

--
Saudações fraternais, 73/51 PY2PVB

Rubens Kamimura
Tel. (18) 3746-8680 ramal 116
Cel. (18) 9-9819-2225 WhatsApp ou (18) 9-9819-2255 


Em seg., 19 de out. de 2020 às 09:59, Evan Hand <elhandjr@...> escreveu:

Rubens,
I would check the audio wiring.  When you changed boxes, did you add an audio amplifier?  If so, see if you can shield the wiring or use a snap-on ferrite to reduce the RF getting into the audio amp.  I suspect that is your issue.

More details including pictures heps us with diagnosing your issue.  By details, I mean any changes in modules or added circuit boards.  Also the new box information; was it a kit like one from AmateurRadioKits?

73
Evan
AC9tu


edoardo marchetti
 

Hi Rubens,
Try to change the antenna, I tried today and I notice a huge reduction in the feedback! The effect lasts until now but it is enormously reduced. So it could be really the rfi. You would better use a dummy load.
73
IU6DBK

On Mon, 19 Oct 2020, 15:16 Rubens Kamimura, <rubens.kamimura@...> wrote:
Evan

Photos

--
Saudações fraternais, 73/51 PY2PVB

Rubens Kamimura
Tel. (18) 3746-8680 ramal 116
Cel. (18) 9-9819-2225 WhatsApp ou (18) 9-9819-2255 


Em seg., 19 de out. de 2020 às 09:59, Evan Hand <elhandjr@...> escreveu:
Rubens,
I would check the audio wiring.  When you changed boxes, did you add an audio amplifier?  If so, see if you can shield the wiring or use a snap-on ferrite to reduce the RF getting into the audio amp.  I suspect that is your issue.

More details including pictures heps us with diagnosing your issue.  By details, I mean any changes in modules or added circuit boards.  Also the new box information; was it a kit like one from AmateurRadioKits?

73
Evan
AC9tu


Evan Hand
 

On Mon, Oct 19, 2020 at 08:10 AM, Rubens Kamimura wrote:
Photos
Rubens,
I do not know what the board is above the low pass filters.  What is it and is that in the correct position?  If it has to do with the audio then it could be the feedback point.  My guess is that is the audio amp for the case speaker.  If that is so, then having it so close to the output could be an issue.  Can you move it more towards the front of the rig, and maybe use coax on the antenna lead?

73
Evan
AC9TU


Rubens Kamimura
 

Oi Marchetti,

GOOD IDEA, I WILL TEST.
 73/51 PY2PVB



Em seg., 19 de out. de 2020 às 13:53, edoardo marchetti <mentorade@...> escreveu:

Hi Rubens,
Try to change the antenna, I tried today and I notice a huge reduction in the feedback! The effect lasts until now but it is enormously reduced. So it could be really the rfi. You would better use a dummy load.
73
IU6DBK

On Mon, 19 Oct 2020, 15:16 Rubens Kamimura, <rubens.kamimura@...> wrote:
Evan

Photos

--
Saudações fraternais, 73/51 PY2PVB

Rubens Kamimura
Tel. (18) 3746-8680 ramal 116
Cel. (18) 9-9819-2225 WhatsApp ou (18) 9-9819-2255 


Em seg., 19 de out. de 2020 às 09:59, Evan Hand <elhandjr@...> escreveu:
Rubens,
I would check the audio wiring.  When you changed boxes, did you add an audio amplifier?  If so, see if you can shield the wiring or use a snap-on ferrite to reduce the RF getting into the audio amp.  I suspect that is your issue.

More details including pictures heps us with diagnosing your issue.  By details, I mean any changes in modules or added circuit boards.  Also the new box information; was it a kit like one from AmateurRadioKits?

73
Evan
AC9tu


 

Rubens,

You are using the V4 uBitx with the audio amp that is powered all the time.

Any RF leak in the case will cause this problem.. you could connect the 12V of the
amp stage to RX12V line and that should solve it.

Try bypassing the speaker leads with a 0.1uF or even shielding it to see if the
feedback stops,

Raj


At 19/10/2020, you wrote:
Evan

Photos

--
Saudações fraternais, 73/51 PY2PVB

Rubens Kamimura
Tel. (18) 3746-8680 ramal 116
Cel. (18) 9-9819-2225 WhatsApp ou (18) 9-9819-2255Â


Em seg., 19 de out. de 2020 Ã s 09:59, Evan Hand <elhandjr@...> escreveu:
Rubens,
I would check the audio wiring.  When you changed boxes, did you add an audio amplifier?  If so, see if you can shield the wiring or use a snap-on ferrite to reduce the RF getting into the audio amp.  I suspect that is your issue.

More details including pictures heps us with diagnosing your issue.  By details, I mean any changes in modules or added circuit boards.  Also the new box information; was it a kit like one from AmateurRadioKits?

73
Evan
AC9tu