Last update 10/8/07

PRECISION STEP ATTENUATORS FOR THE HJFP2 AND HVTP2 MICPRES:

Price $125 for kit, $150 with Assembled units.

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Attenuator Assembly instructions with photos

WHAT ARE PRECISION STEP ATTENUATORS?

Precision step attenuators replace the potentiometers that control the gain of each channel.  A potentiometer or "Pot" is a 3 terminal device, that consists of a resistive material with a wiper the rotates from one end of the resistor to the  other end.  If a signal is put into one end of the resistor, and the other end tied to ground, the wiper will be an output that increases/decreases with rotation angle.  Pots used for controlling gain are generally "Audio taper", which means their output is logarithmic instead of linear with respect to angle.  In simple terms, the Audio Taper (often audio taper pots are marked "AT" or "A" on the back) gives you a better range of control that attenuates equal dB with respect to angle.  Pots generally are +-10% at best in terms of matching

Step attenuators are a multi position switch, where the various "steps" on the switch are precisely calculated attenuation levels using discrete metal film resistors (i.e. low noise).  The ones we offer are 23 step, 2.00dB/step +-0.02dB.  Because the step attenuators are built with discrete resistors, there is far less parasitic capacitance and inductance, which can become a big issue in Pots over (roughly, depends on the circuit to a good extent) 1M.  Here the parasitic components will cause phase shift, and signal dispersion (different frequencies take different amounts of time to get though the pot, making the signal "smeared" in time).  The pots in the kits are 10k, and 250k, which for all practical purposes work great.  However, the step attenuators are better.

TIPS ON BUILDING YOUR OWN

If you choose not to buy the attenuator kits from us and build your own, here's a few tips.  Mouser sells 23 step switches (open frame type), they are around $35 each, the 22 resistors are all different values, and you will have to buy a minimum of 10 each.  The switches and resistors will cost about $96 before shipping.  Make certain you get "shorting" switches as apposed to "non shorting", otherwise they will make a loud "pop" on every step.  Also,  open frame switches will tend to corrode over time, and I've found roughly 50% fail in 10 years.  Military grade hermitically sealed like the ones we buy are ideal.