75 to 50 ohm instrument conversion

For a minimum loss pad, this article should have the losses mentioned: Gotta run...

Does the HP have a hi-Z switch option? If so, you could use a 50 ohm feedthru termination.

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

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

Why not install a nice parallel resistor R = 1/(1/50-1/75) = 150 ohms inside the box?

Cheers

Phil Hobbs

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:

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

That wouldn't help it to display the right level, since it's already .18dB low. :(

Have it your way--minus 150. ;)

It'd work fine in volts.

Cheers

Phil Hobbs

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.

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

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.

I received a note from Avast, they said the Nodbm file is clean and it's in now their database as such :-) Mikek