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https://www.ebay.co.uk/itm/Lucas-Weinsc ... Sw3ANb1ssL
As it looked nice and solid and with N-types I took a chance and bought one.
Picture shows the insides. With a spec as shown I'd guess that its pulse rated (radar??) but for me it will be CW or DATV. Fortunately 100 watt tabbed thick film resistors are available (ali-express for me) and with a little drilling and tapping they will fit nicely under the input/output wires (on RHS of picture. A bit of heatsink+fan on the bottom side and I should have a -20dB attenuator that can cope with high power. It might even improve the bandwidth spec??
Pulse ratings are common for radar components. Peak pulse power ratings of several kW are obtainable from quite small components, especially valves, as long as peak voltage and current ratings are not exceeded. I think the venerable 4CX250K was rated to 8 kW.
If you want a high power, high value, VHF attenuator and have not got one, a high power dummy load and resistive tap works fairly well. That unit you have there might be a good starting point if you change one of the resistors for a 100W tabbed 50 ohm load and the coupling resistor for something appropriate.
I have attached the before and after plots from SATSAGEN showing I THINK somewhat variable attenuation vs frequency but very good VSWR 50MHz-6Ghz.
If I assume that SATSAGEN is 'reasonable' at a specific frequency, I can dial that amount of attenuation into my R&S and get 'about right' readings.
At least It can handle 150W now, although the case may get HOT at that level but nothing another heatsink would't solve. Next project is to mount some attenuators (100watt-20dB) on an old CPU heatsink along with some BNC in & out. Seen on a Russian 2m amp test, looked like a good way for HF/VHF.
Guidance and comments welcome....
all numbers in dBm
1240MHz -30 ?leakage?
2200MHz -27 2300-26 2340 -25 2370 -23 2380 -22 2400 -21 2420 -20 2440 -19 More leakage??
5600MHz -42 5700 -43 5800 -42.
Not exactly 'HP' standard then......
With 100K the theoretical attenuation would be about 75 dB.
As you are not achieving that it would appear the coupling between the two sides is dominating.
It might be worth reducing the value of the resistor. This will reduce the attenuation but will probably give a flatter response. You could probably go as low as 1K which should give you about 30dB. It won’t be a perfectly matched attenuator but it would be usable.
So I THINK I have -40dB power attenuator? With leakage, might try without the 100K 'feed-through' and see if it improves the apparent isolation, especially if I block the tiny hole with a screw).
100R centre pin to centre pin is what I would expect as you have two 50 ohm resistors in series via ground in parallel with a very high value resistor.
In a Pi attenuator the series resistor provides the coupling between input and output. An ideal resistor would give a flat response but as Mike says any leaded component is going to have capacitance and inductance which will affect the frequency response.
I'll try something smaller as suggested and run another plot. Other than the lack of high accuracy, I still have a high power attenuator.....meanwhile I'm mounting this (pictured) on a heatsink. I'd guess it needs a neat machined cavity to be any use at high microwave frequencies.... Gareth