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

G0HZU_JMR · 12th Apr 2021, 11:03 pm

If you list up the key presses for the test I can try and do the tests over the coming weekend.

One test you could do would be to measure the noise floor with 0dB attenuation at 50MHz on a 500kHz span. I have done this test many times over the years. I think I used to set the reference level to -30dBm for this test but when I select the 1Hz noise marker and turn on video averaging I always used to see -147dBm/Hz here. However, when I did this test a few weeks ago it was -146dBm/Hz so maybe it needs a fresh run at the cal/error correction routine.

Back in 2015 I did make up an excel spreadsheet to simulate the signal path for gain/loss and noise figure and IP3 performance and it does show -146dBm/Hz. This would have been based on stage gain/loss measurements I made when I had it apart.

Have you checked the condition of the internal backup battery? This lives on a PCB card in the top unit. See the image below. I think the original battery is under this grey cover but I can't remember what it looks like. I recall that mine had died and I fitted some rechargeables here. Note the amusing spelling 'BATTLY' in the image below.

12th Apr 2021, 11:03 pm	#167
G0HZU_JMR Dekatron Join Date: Sep 2010 Location: Cheltenham, Gloucestershire, UK. Posts: 3,077	Re: Spectrum Analyser TR4172 If you list up the key presses for the test I can try and do the tests over the coming weekend. One test you could do would be to measure the noise floor with 0dB attenuation at 50MHz on a 500kHz span. I have done this test many times over the years. I think I used to set the reference level to -30dBm for this test but when I select the 1Hz noise marker and turn on video averaging I always used to see -147dBm/Hz here. However, when I did this test a few weeks ago it was -146dBm/Hz so maybe it needs a fresh run at the cal/error correction routine. Back in 2015 I did make up an excel spreadsheet to simulate the signal path for gain/loss and noise figure and IP3 performance and it does show -146dBm/Hz. This would have been based on stage gain/loss measurements I made when I had it apart. Have you checked the condition of the internal backup battery? This lives on a PCB card in the top unit. See the image below. I think the original battery is under this grey cover but I can't remember what it looks like. I recall that mine had died and I fitted some rechargeables here. Note the amusing spelling 'BATTLY' in the image below. Attached Thumbnails __________________ Regards, Jeremy G0HZU