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no transmit on UBITX6


Vince KA2GRD
 

My new UBITX6 was not transmitting. Seemed to recieve OK.  I replaced the RF power transitors. still no transmit and the TX indicator on the LCD panel flickerswhen I key the mic. 
Anyone know anything about this?

Vince
KA2GRD


Evan Hand
 

Vince,

Have you tried CW and the Key input rather than the Mic and PTT to verify that the transmitter power section is working?  That is where I always start when I have a transmission problem.  This step isolates where it is in the power amp section of the rig or in the IF and audio sections.

The intermittent PTT could be a bad connection in the mic or in the rig.  If you have another stereo 3.5mm plug, tip ring sleeve (TRS) NOT tip ring ring sleeve (TRRS) I would try that and short out the PTT (ring to sleeve) to see if that keeps the uBITX in the transmit mode.

I would also make sure that your power supply can handle the 2.5amps at 12 volts.  If the supply is drooping, that would also cause the rig to drop out of transmitting.

73
Evan
AC9TU


Bob Lunsford
 

I do not suggest that this is the problem but believe it is an appropriate place to remind anyone who may be new to the forum that a simple, transformer-rectifier-capacitor wall-wart is not good power supply to use with the uBITX radios or any other QRP rig. The reason is that if the wall-wart label says 12V 5A, the voltage listed is what the wall-wart will produce AT 5A ... however ... when it is only drawing 1 or 2 Amps, the voltage may well be as high as 16 or 18V...! In other words, the voltage is at the rated amperage so if you draw less from the wall-wart, the voltage is significantly higher. This higher voltage is what we'd find when the radio is in receive and 16-18 Volts is much too high to risk blowing the receiver.

There are wall-wart supplies with switching/solid state rectifier systems inside the wall-wart and if it says 13.8V 5A, the unit can be used for up to 5A and the voltage remains the same.

With any QRP rig, saving money on the power supply can not be done if it results in extensive repairs. A good, modern supply is a good investment here. Good supplies cost only $25-$35 US and are well worth it. But careful shopping at flea markets can be surprising. For example, a good Regency power supply cost me less than $10 and it is rated at 13.8V 5A and is not much bigger than a grapefruit. Even though made 60 or more years ago, it's sturdy and stable and good enough for any of the 10W QRP rigs. 

Bob — KK5R

On Wednesday, November 25, 2020, 3:55:22 PM EST, Evan Hand <elhandjr@...> wrote:


Vince,

Have you tried CW and the Key input rather than the Mic and PTT to verify that the transmitter power section is working?  That is where I always start when I have a transmission problem.  This step isolates where it is in the power amp section of the rig or in the IF and audio sections.

The intermittent PTT could be a bad connection in the mic or in the rig.  If you have another stereo 3.5mm plug, tip ring sleeve (TRS) NOT tip ring ring sleeve (TRRS) I would try that and short out the PTT (ring to sleeve) to see if that keeps the uBITX in the transmit mode.

I would also make sure that your power supply can handle the 2.5amps at 12 volts.  If the supply is drooping, that would also cause the rig to drop out of transmitting.

73
Evan
AC9TU