RE: 6.25 Watt Hamradio Dummy Load

shabaz — Fri, 31 May 2019 14:30:27 GMT

Hi Bernhard,

I don't think this will operate in GHz region. You can see the difference the construction makes, here (there is a small BNC there, that only works to 100MHz for instance): Which 50 ohm Loads are any good? Finding out with the FPC1500 Vector Network Analyzer

(There is my (awful) home-made construction there, which cannot work beyond HF, but there is also a commercial one (BNC terminator) there which is poor beyond a few hundred MHz (mainly because it is not intended for radio, it is intended for LAN termination).

So from that experience, I believe there is a large amount of inductance in the design, due to the chains of resistors. Is it a dummy load, or an attenuator? I think it's an attenuator, but in this case the best way is to use this website (it is awesome): https://www.changpuak.ch/electronics/calc_02.php

Using that topology (pi or T), you'll get a perfect match for source and load (albeit still only in theory, since it still depends on construction).

The topology you have will result in a mismatch at the end marked 'output', so a symmetrical design is preferred.

In your case, if you need to attenuate a lot, then perhaps an option is to do it in stages, since it gets awkward to attenuate more than (say) 30dB in one stage. Also, another option is to use parallel resistors (e.g. stacked on top of each other) rather than serial strings of resistors.

RE: 6.25 Watt Hamradio Dummy Load

jw0752 — Fri, 31 May 2019 14:14:28 GMT

Hi Bernhard,

This looks like a very nice and well built dummy load.

John