Hi Dave

?????????????? Checked the signals and they are all exactly harmonically related, dropping the input to the spec analyzer by 9db with fixed attenuators just lowers the signals by 9db so it is not overdriving the spec analyzer

Setting the generator to 600 mhz does lower the harmonics but they are then 600 mhz apart

By the time I get to 1ghz the harmonics are -40 db down from the fundamental which is not too bad

So whatever is causing the problem, which the service manual suggest could be low drive in to the internal mixer, is only mainly affecting the lower portion of band 0 below about 500 mhz to any great extent.

Time to measure the 3.9 ghz ?signal level into the mixer which I tried to do yesterday but with the cables I had I had to use a 2m length of rg58 to get the right connectors so the attenuation at that frequency would be pretty high.

Trying to find some figure was impossible so I took a wild guess at the figure and came up with about 5 db when added to the level of 5.4 db I measured means the signal is only about 10.4 db well below the 13.5 db specified.

So on the way home yesterday I brought a N to SMA adaptor so I ?can put the power sensor right at the end of the hard line to measure the input into the mixer.

If that signal is low then I need to chase back through the circuit to see where it is being lost.

I have had to mechanically dismantle some of the case to get to the hard line SMA connectors as it is tucked in under the side rails of the chassis

Hope it is not one of those modules down there in the RF section as the manual warns that they are not repairable and very expensive and by now probably unobtainium other than from a parts unit.

Will advise further

Ken

VK2TKE

Sent from for Windows 10

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