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The 1 KHz (or 400 hz) signal I'm referring to is the one you measure the S/N ratio on. Thats the post detection audio signal, which is present at the speaker terminals, and back at the right side of the am detector diodes. The pre-dectection C/N ratio would be measured in the I/F stages, for instance, where the signal is at 7.8 MHz.

When Robb made his measurement, did he not use a 1 KHz test signal (I thought he did)? Also, thats why the intrest in moving from 400 Hz to 1 Khz.

Some radios will recover 400 Hz audio, so your mileage will vary. Mine starts to die there, so I moved up to 1 Khz. Caught me by surprize, so I started exploring the audio freq response and looking for the specs on it. You will most likely get it to work at 400 Hz, but you could be at the lower edge of the audio pass band, which will degrade the SINAD. Give it a try anyway, press on. !!

For instance, the Kenwood TS-120 HF radio has an audio frequency response of 400-2600 Hz (the band edges of the audio). Your modulating signal on the carrier needs to be in the 1 Khz range to characterize the best possible SINAD.

<blockquote data-quote="KG6YGE" data-source="post: 415731" data-attributes="member: 28834">The 1 KHz (or 400 hz) signal I&#039;m referring to is the one you measure the S/N ratio on. Thats the post detection audio signal, which is present at the speaker terminals, and back at the right side of the am detector diodes. The pre-dectection C/N ratio would be measured in the I/F stages, for instance, where the signal is at 7.8 MHz. When Robb made his measurement, did he not use a 1 KHz test signal (I thought he did)? Also, thats why the intrest in moving from 400 Hz to 1 Khz.Some radios will recover 400 Hz audio, so your mileage will vary. Mine starts to die there, so I moved up to 1 Khz. Caught me by surprize, so I started exploring the audio freq response and looking for the specs on it. You will most likely get it to work at 400 Hz, but you could be at the lower edge of the audio pass band, which will degrade the SINAD. Give it a try anyway, press on. !!For instance, the Kenwood TS-120 HF radio has an audio frequency response of 400-2600 Hz (the band edges of the audio).&nbsp; Your modulating signal on the carrier needs to be in the 1 Khz range to characterize the best possible SINAD.</blockquote>

[QUOTE="KG6YGE, post: 415731, member: 28834"] The 1 KHz (or 400 hz) signal I'm referring to is the one you measure the S/N ratio on. Thats the post detection audio signal, which is present at the speaker terminals, and back at the right side of the am detector diodes. The pre-dectection C/N ratio would be measured in the I/F stages, for instance, where the signal is at 7.8 MHz. When Robb made his measurement, did he not use a 1 KHz test signal (I thought he did)? Also, thats why the intrest in moving from 400 Hz to 1 Khz. Some radios will recover 400 Hz audio, so your mileage will vary. Mine starts to die there, so I moved up to 1 Khz. Caught me by surprize, so I started exploring the audio freq response and looking for the specs on it. You will most likely get it to work at 400 Hz, but you could be at the lower edge of the audio pass band, which will degrade the SINAD. Give it a try anyway, press on. !! For instance, the Kenwood TS-120 HF radio has an audio frequency response of 400-2600 Hz (the band edges of the audio). Your modulating signal on the carrier needs to be in the 1 Khz range to characterize the best possible SINAD. [/QUOTE]

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