Wide-band doubler feedthrough suppression; 3 MHz - 3 GHz in - Page 1
Forum section: electronics / rf-microwave

author: ezalys
author_rank: Frequent Contributor
timestamp: November 24, 2018, 05:57:38 pm
content: Hey all,I'm curious how the doubler inside the 85047A test set works, since it seems to go from 1.5 MHz up to 3 GHz. Since the doubler is engaged while measuring from 0-3, it must also have excellent feedthrough supression as well. Any idea how they may have accomplished this?E

author: hendorog
author_rank: Super Contributor
timestamp: November 24, 2018, 08:09:45 pm
content: I haven't tested one of the real HP doublers, and haven't seen inside one either so can't answer your question.However I did manage to build one which the 8753 will use without showing errors. So it is possible to build one yourself instead of forking out $1K for an 85047A just to measure to 6GHz.If the doubler doesn't suppress the harmonics or fundamental sufficiently then the 8753 will show lock errors. (I don't know the definition of 'sufficiently' unfortunately)For mine I used a couple of minicircuits wideband baluns either side of an avago quad diode package - discontinued now.

author: edavid
author_rank: Super Contributor
timestamp: November 25, 2018, 12:14:42 am
content: Quote from: ezalys on November 24, 2018, 05:57:38 pmIf you look at the specs closely, it appears that there is a typo, and the doubler is only used above 3GHz.Other HP doublers, such as the 10515A and 11721A, use a simple center tapped transformer + full wave rectifier circuit.

author: hendorog
author_rank: Super Contributor
timestamp: November 25, 2018, 01:46:30 am
content: Quote from: edavid on November 25, 2018, 12:14:42 amI don't think that is a typo. The start freq of high range is 3MHz as presumably that is the lower limit of the doubler. I guess limited by the frequency range of the balun/transformer. inside the doubler.AFAIK the entire sweep changes to high range any time the sweep ends > 3GHz, it doesn't switch mid sweep between ranges. If it was switching in the middle of a sweep it would have to be a solid state switch and I am 99.9% sure that the transfer switch is just an ordinary mechanical coax switch. OTOH the output port switches are solid state unless you have a unit with option 009.This is the doubler transfer switch part listed in the service manual:https://www.ebay.com/itm/HP-Agilent-5180-8449-Coaxial-Switch-DC-to-6-GHz-/271245448404

author: edavid
author_rank: Super Contributor
timestamp: November 25, 2018, 03:06:54 am
content: Quote from: hendorog on November 25, 2018, 01:46:30 amAs an example, the insertion loss spec is:4 dB +0.8 dB/GHz: 300 kHz to 3 GHz17.5 dB +0.8 dB/GHz: 3 GHz to 6 GHzIf itdidn'tswitch in the middle of the sweep, they would have to specify the higher insertion loss e.g. for a sweep from 2-4GHz, but they don't.

author: hendorog
author_rank: Super Contributor
timestamp: November 25, 2018, 03:15:38 am
content: Quote from: edavid on November 25, 2018, 03:06:54 amI'm seeing the insertion loss spec written like this in the 85047A service manual on page 5 (this is for the solid state switch version):RF In to Port 1,24 dB +0.8 dB/GHz:3 GHz Range17.5 dB +0.8 dB/GHz:6 GHz Rangehttps://literature.cdn.keysight.com/litweb/pdf/85047-90001.pdf

author: TheSteve
author_rank: Unknown
timestamp: November 25, 2018, 03:20:49 am
content: In the service manual it shows the signal path for .300 to 3000 MHz and for 3 to 6000 MHz. It seems pretty clear that if you go above 3 GHz it uses the doubler path for everything and raises the lower minimum frequency to 3 MHz. This only applies to units that have a 3 GHz only source, if they have a 6 GHz source(newer units) then the doubler is never used and you can go .3 to 6000 MHz in a single sweep.

author: edavid
author_rank: Super Contributor
timestamp: November 25, 2018, 03:50:28 am
content: Quote from: hendorog on November 25, 2018, 03:15:38 amHere's a datasheet that lists it the other wayhttp://www.testequipmenthq.com/datasheets/Agilent-85047A-Datasheet.pdf

author: hendorog
author_rank: Super Contributor
timestamp: November 25, 2018, 04:00:42 am
content: Quote from: edavid on November 25, 2018, 03:50:28 amYep fair point. However I am sure that is the typo.