DX-70 Sideband leakage

[ashok.das81]

Hi all,

My radio Alinco DX-70 transmits on both USB and LSB, when I set it to transmit on USB. Signal is visible in USB as well as in LSB, but signal strength is bit less in LSB. It appears that radio is transmitting as DSB. Now my question how this can happen. What could be the problem that makes a SSB radio to DSB ? One more observation is that, when I transmit on LSB, then it is fine, there is no transmission on USB at this time. I need some help as how to diagnose this problem. At least if I can understand where is the problem, then I can determine if it repairable or not.

Thanks

[iMo]

First step is to get the "DX-70 Service Manual" where you may find the schematics.
On the page 58 you may find the block diagram where you may see the most of the modes switching is done via diodes, so doublecheck them.

[CaptDon]

How do you know this to be true? Looking at signal with a spectrum analyzer? Listening on another radio which may be at fault? Generally speaking they use a crystal filter and in the mixing stages shift the carrier above the upper cutoff to obtain the lower sideband, or shift the carrier below the lower cutoff to obtain the upper sideband. Could be a crystal filter problem or improper carrier offset for upper and lower sideband generation or your measuring equipment is faulty and the radio is fine.

[geggi1]

If you have problem with the BFO or crystal filter you will get some of the opposite side band.
If it is only on one sideband its most likely the crystal filter.