UK Vintage Radio Repair and Restoration Discussion Forum - View Single Post - 6-gang FM stereo tuner heads

G0HZU_JMR · 24th Nov 2022, 11:43 pm

The diagram below shows how I would normally set up an IP3 measurement. I'd start with 3dB attenuators as indicated and then increase them if required.

The setup below is usually good enough, unless trying for a measurement with very low IMD levels. I'd be happy to use the setup below to carry out an initial check on a mixer. With some mixers the LO drive level can make a big difference. It is also worth playing around with the RF tone levels and the RF and LO frequencies to see how the result changes.

A modern (strong) lab analyser won't need a diplexer at the IF port, but the internal attenuator needs to be set such that the analyser's internal IMD is at least 20dB lower than the mixer IMD. A good margin is needed here because the analyser also sees the image test tones as well as the wanted tones.

24th Nov 2022, 11:43 pm	#265
G0HZU_JMR Dekatron Join Date: Sep 2010 Location: Cheltenham, Gloucestershire, UK. Posts: 3,077	Re: 6-gang FM stereo tuner heads The diagram below shows how I would normally set up an IP3 measurement. I'd start with 3dB attenuators as indicated and then increase them if required. The setup below is usually good enough, unless trying for a measurement with very low IMD levels. I'd be happy to use the setup below to carry out an initial check on a mixer. With some mixers the LO drive level can make a big difference. It is also worth playing around with the RF tone levels and the RF and LO frequencies to see how the result changes. A modern (strong) lab analyser won't need a diplexer at the IF port, but the internal attenuator needs to be set such that the analyser's internal IMD is at least 20dB lower than the mixer IMD. A good margin is needed here because the analyser also sees the image test tones as well as the wanted tones. Attached Thumbnails __________________ Regards, Jeremy G0HZU