Ilkka,
I use an HP 778D 20dB directional coupler for this application. 1kW
applied yields 10W at the -20dB decoupled port, then I just use an ordinary
20W attenuator (Bird, Narda, HP, whatever -- lots of them available) plugged
into the spectrum analyzer. The 20 dB directional couplers are readily
available surplus for about $100 or so, picked up my last one from Fair
Radio Sales in Ohio, USA http://www.fairradio.com
73 de Steve, WB2WIK/6
"Each success only buys an admission ticket to a more difficult problem." --
Henry Kissinger
> -----Original Message-----
> From: ilkka.kontola@nokia.com [SMTP:ilkka.kontola@nokia.com]
> Sent: Wednesday, May 22, 2002 11:37 PM
> To: amps@contesting.com
> Subject: [Amps] Homemade attenuator or sampler for 1+kW?
>
> Any ideas for an inexpensive and safe way to connect RF spectrum analyzer
> to 1+ kW HF or 6m or 2m linear amplifier? I have HP 8594E in my home lab
> but I do not own any professional 1 kW level attenuators or signal
> samplers.
>
> I do have MFJ "cantenna" for HF/6m and for 2m I could use couple of
> hundred
> meters of RG213 to improve the return loss.
>
> I have been considering Bird 4273 and 4275 to cover both HF and VHF..
> http://www.rfparts.com/bird2.html#4275 . BTW, any hints who is selling
> them in Europe?
>
> What is the topology of the Bird samplers? A capacitive voltage
> divider and a 50 ohm resistor between the lower capacitor and
> output connector?
>
> Has anybody constructed a resistive 1+ kW sampler? The dummy load
> would operate as the first resistor of a "pi" attenuator and the sampler
> would
> contain the other two. In order to keep the dissipation of the first
> sampler
> resistor (or middle resistor of the whole pi) in few watts the attenuation
> has
> to be in order of 60 or 70 dB. The parallel capacitance of the resistor
> (or resistors in a string) surely creates some challenges.
>
> Safety or reliability _is_ a big issue since I do not want to blow up my
> spectrum analyzer.
>
> 73, Ilkka OH3NJC
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