I just bought an HP3586B Selective Voltmeter. It has a 75 ohm input, I'll be modifying it for 50 ohms. An L pad has a power loss of 5.72db, what is the change if I just plug a 50 ohm source into the 75 ohm input? Is it and addition of power loss?
Thanks, Mikek
For a minimum loss pad, this article should have the losses mentioned: Gotta run...
-- Jeff Liebermann jeffl@cruzio.com 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558
Does the HP have a hi-Z switch option? If so, you could use a 50 ohm feedthru termination.
-- John Larkin Highland Technology, Inc picosecond timing precision measurement jlarkin att highlandtechnology dott com http://www.highlandtechnology.com
Thanks Jeff, I had looked at that page, I was disappointed to see the minimum power loss was 5.72db. So then I wondered about just connecting the 50 ohm source to the 75 ohm input, What is my loss there? Mikek
Interesting it has an input that is 75 ohm or switched to 10k/50pf. Also jacks for 124 ohms, 135 ohms, and 600 ohms. So maybe I could use a 50 ohm termination, but only up to a few MHz before the 50pf starts having a noticeable affect. Still looking for a better solution. Mikek
According to the service manual, (0358690002V2) you add .18 dB to the displayed level
-- Never piss off an Engineer! They don't get mad. They don't get even. They go for over unity! ;-)
Can't you simply open up that termination 'box' and change the termination to 50 Ohms?
Or add 150 Ohms in parallel in a BNC adapter? ...Jim Thompson
-- | James E.Thompson | mens | | Analog Innovations | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | STV, Queen Creek, AZ 85142 Skype: skypeanalog | | | Voice:(480)460-2350 Fax: Available upon request | Brass Rat | | E-mail Icon at http://www.analog-innovations.com | 1962 | Why is it that the most unproductive members of our society blame the most productive members of our society for their failures?
Why not install a nice parallel resistor R = 1/(1/50-1/75) = 150 ohms inside the box?
Cheers
Phil Hobbs
-- Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC Optics, Electro-optics, Photonics, Analog Electronics 160 North State Road #203 Briarcliff Manor NY 10510 hobbs at electrooptical dot net http://electrooptical.net
I haven't got it yet to open up, but from what I read, there is plenty of room, so maybe that is the solution. Mikek
I'll have to read some more, I thought I saw somewhere to add 0.2db for a 50 ohm source, but I had not yet had the question. When I went looking for that answer, I could not find it, Thanks, Mikek
Get the manuals from the OEM's website:
-- Never piss off an Engineer! They don't get mad. They don't get even. They go for over unity! ;-)
dB's are for sissies. See NOdBm.zip on the Simulation Tools & Macros Page of my website >:-}
Provoked by customer specs, "Input must withstand +20dBm". ...Jim Thompson
-- | James E.Thompson | mens | | Analog Innovations | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | STV, Queen Creek, AZ 85142 Skype: skypeanalog | | | Voice:(480)460-2350 Fax: Available upon request | Brass Rat | | E-mail Icon at http://www.analog-innovations.com | 1962 | Why is it that the most unproductive members of our society blame the most productive members of our society for their failures?
That wouldn't help it to display the right level, since it's already .18dB low. :(
-- Never piss off an Engineer! They don't get mad. They don't get even. They go for over unity! ;-)
Have it your way--minus 150. ;)
It'd work fine in volts.
Cheers
Phil Hobbs
-- Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC Optics, Electro-optics, Photonics, Analog Electronics Briarcliff Manor NY 10510 hobbs at electrooptical dot net http://electrooptical.net
My way would be to remove the option that converted it to 75 Ohms, and re-calibrating it. I had looked into it a while back, but I decided to keep my HP312B instead.
-- Never piss off an Engineer! They don't get mad. They don't get even. They go for over unity! ;-)
25 ohms (both ends) and 50 pF is down 3 dB at 127 MHz.
-- John Larkin Highland Technology, Inc picosecond timing precision measurement jlarkin att highlandtechnology dott com http://www.highlandtechnology.com
Well, I'll probably take the sissy route for my relative measurements. My plan is to measure the outputs of several ferrite loop antennas. So all I need to know is more power is better. I do see, Input Volts = (0.075)10^(A/10) where A is the displayed power amplitude. My Avast did not like your NOdbm program! But it ran OK.
Mikek
My son, Aaron, wrote that for me when he was a student at UofA... he's now 47 years old ;-) ...Jim Thompson
-- | James E.Thompson | mens | | Analog Innovations | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | STV, Queen Creek, AZ 85142 Skype: skypeanalog | | | Voice:(480)460-2350 Fax: Available upon request | Brass Rat | | E-mail Icon at http://www.analog-innovations.com | 1962 | Why is it that the most unproductive members of our society blame the most productive members of our society for their failures?
Same as putting a 75 ohm load on a 50 ohm transmitter. That produces a return loss of 14dB, which is 0.177dB mismatch loss: Source = 50 ohms Load = 75+j0 ohms
Overkill at its best: "HP3586B selective level meter shown as HF receiver" I use my service monitors (IFR-1500, Wavetek 3000b) in much the same way. Congrats.
-- Jeff Liebermann jeffl@cruzio.com 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558
I received a note from Avast, they said the Nodbm file is clean and it's in now their database as such :-) Mikek
ElectronDepot website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.