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WTB HP 11852A or B 50/75 Ohm minimum loss pad

 

Hi
I'm looking for a pair of the HP 11852A or B 50/75 Ohm minimum loss?pad adapters or their
equivalents. If there is someone that doesn't need them I'm willing to buy them. I'm located at Athens GREECE so will have to ship them with post if possible for economy... reasons :)
Thank you in advance
Sotiris Pdmt
 

How good do they have to be?

How about?the Mini-Circuits UNMP-5075?? They have a ship from UK option.



On Sat, Apr 25, 2020 at 8:37 AM Sotiris via <pdmtr=[email protected]> wrote:
Hi
I'm looking for a pair of the HP 11852A or B 50/75 Ohm minimum loss?pad adapters or their
equivalents. If there is someone that doesn't need them I'm willing to buy them. I'm located at Athens GREECE so will have to ship them with post if possible for economy... reasons :)
Thank you in advance
Sotiris Pdmt

 

I want to use them for an HP 85046B to make 50R testing. I know that is not the best solution but for my use the results will be acceptable. So I guess the best the pads will be the better results will be at the end.
 

¿ªÔÆÌåÓý

Maxim has an application note with equations for designing minimum loss pads:

As a learning experience, I laid out a PCB with an F connector on the 75 Ohm end and an SMA on the 50 Ohm end.

?

On 4/27/20 3:18 PM, Sotiris via groups.io wrote:

I want to use them for an HP 85046B to make 50R testing. I know that is not the best solution but for my use the results will be acceptable. So I guess the best the pads will be the better results will be at the end.

 

I built myself a 50 ohm to 75 ohm matching pad using 3 resistors from a formula or calculator on the Internet a few years ago.? I don't think it's quite minimum loss, though.? Almost exactly 6 dB rather than 5.7 dB, but I figured having a nice round number was better than setting it to absolute minimum.? I removed an F connector for the 75 ohm side from some widget I probably got out of the trash at a former employer, grabbed an SMA for the 50 ohm side from my stash, and soldered them and the resistors to a little board I had lying around, eval board for somebody's SOT-89 amplifier or something.? Not hard to do, and I wanted to be able to look at the spectrum of the IF coming from my satellite dish without introducing ripple from the mismatch.? Yep, it works; I can see a bunch of modulated carriers.? No visible ripple.? I haven't tried it straight F connector to SMA to see if there's a difference (yet).

Jim Ford

------ Original Message ------
From: "BobH" <wanderingmetalhead@...>
Sent: 4/27/2020 8:15:43 PM
Subject: Re: [HP-Agilent-Keysight-equipment] WTB HP 11852A or B 50/75 Ohm minimum loss pad

Maxim has an application note with equations for designing minimum loss pads:

As a learning experience, I laid out a PCB with an F connector on the 75 Ohm end and an SMA on the 50 Ohm end.

?

On 4/27/20 3:18 PM, Sotiris via groups.io wrote:
I want to use them for an HP 85046B to make 50R testing. I know that is not the best solution but for my use the results will be acceptable. So I guess the best the pads will be the better results will be at the end.

 

The Mini Circuits minimum loss pads meet or exceed the specifications of the HP ones and for $30US new you can't go wrong.

Greg
 

Hi all
Thanks for the replies.
Yes I 've checked the mini circuits pads and seems to be the best way to go! I've to order a pair of them now!
 

Hi all,

why not build some pads?
All you need is 3 86.6 Ohm SMD resistors and two RF connectors of your choice and some copper clad FR4.
See pictures at , text in Swedish but I think the pictures will show what you need.

Best regards
Marcus, SA5PMG
 

The main gotcha about DIY pads is if you use them over a wide band of frequencies when making farily accurate measurements with instruments such as VNAs.? Unless you follow microwave layout techniques and use components rated for same you will find that you will not have a very flat response over frequency as the inductances and capacitances begin to creep in at the higher frequencies.

?

I once was designing with a fellow who had spent the majority of his life working on microwave circuits.? We were designing a low power RF product that operated at 2 GHz and all components were mounted on a ?printed circuit board.? There was a SMD resistor in a portion of the circuit that was rather unusual for its location.? I had to ask what he was doing with it and he replied that he had chosen a resistor that became very inductive at the operating frequency but still provided the necessary DC bias current for proper operation.? My only concern was if the purchasing department decided to find a second source and the component characteristics changed.? He made a specific requirement on the BOM that the manufacturer/part number always be the same explaining as to why.

?

From this a $30 off-the-shelf pad with characterized parameters starts to look pretty good.

?

Greg
 

Hi all,

as always you get what you pay for and you always need to be aware of equipment's quirks and limitations, home-made or not. My home made pads are good to at least 1.2GHz (see VNA picture in link). And that is with cheap no name 1% 1206 resistors.

But as Greg explains at higher frequencies (>2GHz) they start to have higher loss. See fresh measurement below.
Best regards
Marcus
 

On 2020-05-02, at 16:42, Marcus Gustafsson <mankan@...> wrote:

See pictures at this page, text in Swedish but I think the pictures will show what you need.
(With link to .)

Requiring registration to view the pictures and then doing the CAPTCHA in Swedish is mean.
Fortunately, duckduckgo is your friend.
Now waiting for manual intervention...

(Ham.se would be a great name for a German shop :-)

Gr¨¹?e, Carsten
 

Thanks Carsten,

I was not aware of the registration requirement on ham.se for seeing picture, thanks for telling me.

Here comes the pictures of my pad build and initial measurements.

Br
Marcus
 

It looks like good success has been made in DIY pads.? The nice aspect of a small project like this is that being able to make simple changes can bring about good results quickly.? But when you may have need for many of them in a commercial environment it is easier to pay a little more for OTS products.

?

Greg

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