Need to Measure Transmitter Spurs, w/o Spectrum Analyzer

That is really cool. I'm amazed that they can get that kind of attenuation in a single IC. I tried using a digital potentiometer as a variable attenuator, and even at low RF, the leakage was incredible. Apparently that IC is "special."

 

It takes considerable time and effort making attenuators that perform well through VHF and beyond. I just bought commercial/lab attenuators instead.

The fifty watters do double duty as dummy loads and attenuators, when using the tx audio, or spectrum analyzers. Obviously the "ON" time must be kept short for higher power levels, and in those instances I also use a small fan.

The 355 step attenuators are a great help some times.

 

Nice... Thank you for the info. Just what I need for a project.

Ed

 

Be aware that's it's only good for a 1/4 watt of dissipation.

 

IC based attenuators are sweet. On the Analog Devices AD9361, the on chip transmit attenuator has a range of 89.75 dB in 0.25 dB steps.

http://www.analog.com/en/products/r...eceivers/wideband-transceivers-ic/ad9361.html

http://www.farnell.com/datasheets/2007082.pdf

 

It takes considerable time and effort making attenuators that perform well through VHF and beyond. I just bought commercial/lab attenuators instead.

I agree; I built my switched attenuator "just because I wanted to" but I also have commercial units.

This was assembled from three Telonics-Berkeley units; I put them in the case;



The 10dB/ & the 1dB/ units were found here in VK at very reasonable prices and it was initially a "two-knob" build; I later added the 0.1dB/ unit which was found on ebay at a reasonable price.

Ebay prices are now, several years afterwards, no longer reasonable; I'm glad I got them when I did.

This one, using an attenuator salvaged from a Wavetek sweep generator and housed by me, probably gets the most use; I put it inline with my spectrum analyser to ensure no expensive blow-ups;



In addition, there are probably some dozens of fixed attenuators; I also have an attenuator "chip" that I will put on a heatsink some day to make a 100W unit.

Be aware that (the SV1AFN device is) only good for a 1/4 watt of dissipation.

True; it may not suit everyone.

High power can be reduced prior to a low-power unit with a suitable fixed attenuator, power tap or coupler.

I've thought about building the deservedly-popular W7ZOI power tap but, with my other tools for reducing power, I don't really need it.

I have several commercial couplers but I also use home-made couplers, eg;





Performance is quite good; coupling is still 32dB at 150 MHz.

 

They work very well at the 5 W level. The temperature rise after dissipating 4.5 W for a whole day as level setting attenuators was about 20 C.
It was impossible to detect any attenuation drift after operation.
73/
Karl-Arne
SM0AOM

 

Mini-Circuits is definitely quality parts -- I work in RF test and measurement and the vast majority of the connectors, splitters, pads, etc. I use on the job are from Mini-Circuits.

I have one of their 40 dB attenuators that I use when testing high power (high-hundreds of watts) devices and I trust it completely not to fail and fry the front end of the six-figure spectrum analyzer I use for measurements

Best quality/price ratio out there in my opinion.

 

How about power to weight ratio ?

 

I was also surprised that the Elecraft attenuator was only specified for 2W of power. I looked at the parts list, and all of those resistors are rated for either 1W or 2W. When I did the calculation on all of the Pi sections, with all sections in-line, there wasn't a single resistor that exceeded 1W of dissipation with 5W of input, and the closest was 0.77W, IIRC. It did require all sections to be engaged, but in that configuration, the step-down was gradual enough to keep all of the resistors in-range of their ratings.