UK Vintage Radio Repair and Restoration Discussion Forum - View Single Post

g4wim_tim · 10th Jan 2019, 8:57 pm

Thanks to the help and generosity of members of this forum I now have the tx operating on 160, 80 and 60 mtrs.

It's producing a nice clean 50 watts of carrier and easily runs up to 100 % modulation.

The following pictures show the modulation envelope / spectrum at 75 and 99% modulation.

Harmonics of the 1kHz modulation are approx 24dB down at full power and modulation.

I had to juggle with the plate / screen modulation ratios to get a nice trapezoid shape and adjust the screen phase compensation.

The modulation frequency response is 340Hz to 3.5kHz at -3dB.

The other spectrum shows PSU ripple on the carrier down at about -36dB, not as low as I would like but seems to be due to ripple on the PA HT line.

Still needs a few mechanical items fixing up, but basically ready for air testing - wish me luck

Regards Tim

10th Jan 2019, 8:57 pm	#20
g4wim_tim Pentode Join Date: Nov 2018 Location: Freckleton, Lancashire, UK. Posts: 232	Re: 160 /80 / 60 mtr AM TX project Thanks to the help and generosity of members of this forum I now have the tx operating on 160, 80 and 60 mtrs. It's producing a nice clean 50 watts of carrier and easily runs up to 100 % modulation. The following pictures show the modulation envelope / spectrum at 75 and 99% modulation. Harmonics of the 1kHz modulation are approx 24dB down at full power and modulation. I had to juggle with the plate / screen modulation ratios to get a nice trapezoid shape and adjust the screen phase compensation. The modulation frequency response is 340Hz to 3.5kHz at -3dB. The other spectrum shows PSU ripple on the carrier down at about -36dB, not as low as I would like but seems to be due to ripple on the PA HT line. Still needs a few mechanical items fixing up, but basically ready for air testing - wish me luck Regards Tim Attached Thumbnails __________________ Building and tinkering for over 50 years, from 807's to digital amateur TV.