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Alan_G3XAQ · 6th Jul 2020, 11:03 am

The guy on the HP forum who has successfully modified an 8568B+8444A to use all 3 LOs and keep the TG transparent down to the SA noise floor has gone to some lengths to keep the reverse isolation high. He has a chain of isolators on the LO1 and LO2 signal feeds and a lot of bandpass filtering on LO3.

I was being tempted by all this because I need to replace the broken LSI output stage on the 8884A that is coming as part of the Cyprus package. One route might have been to buy a second TG just for its output stage and then I'd have most of that one left doing nothing. In the event the local chap with a TG for sale wants more than I can thoil so I'm going cold on the idea anyway. You two telling me it it's a bad idea is another nail in the coffin.

It's a shame that I'll be ending up with a system that is in some ways less functional than my old TF2370. I don't have space to keep both. Maybe I need to become more used to using my NanoVNA and the PC screen grabber although cluttering up the bench with a laptop whenever I want to use it feels clunky to me. Of course, if David has one of those HP VNAs he mentioned for sale for a lot less than the prices on eBay...

73, Alan G3XAQ

6th Jul 2020, 11:03 am	#121
Alan_G3XAQ Pentode Join Date: Apr 2018 Location: Canterbury, Kent, UK. Posts: 189	Re: Replacement for HP8640B signal generator The guy on the HP forum who has successfully modified an 8568B+8444A to use all 3 LOs and keep the TG transparent down to the SA noise floor has gone to some lengths to keep the reverse isolation high. He has a chain of isolators on the LO1 and LO2 signal feeds and a lot of bandpass filtering on LO3. I was being tempted by all this because I need to replace the broken LSI output stage on the 8884A that is coming as part of the Cyprus package. One route might have been to buy a second TG just for its output stage and then I'd have most of that one left doing nothing. In the event the local chap with a TG for sale wants more than I can thoil so I'm going cold on the idea anyway. You two telling me it it's a bad idea is another nail in the coffin. It's a shame that I'll be ending up with a system that is in some ways less functional than my old TF2370. I don't have space to keep both. Maybe I need to become more used to using my NanoVNA and the PC screen grabber although cluttering up the bench with a laptop whenever I want to use it feels clunky to me. Of course, if David has one of those HP VNAs he mentioned for sale for a lot less than the prices on eBay... 73, Alan G3XAQ