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Radio Broadcast Technical Consulting and Sales
10032 Island Drive, Brainerd, MN  56401

Zercom Broadcast Products

Note:  A limited quantity of new units are available at this time.


Zercom ZH-2 Telephone Hybrid

Rack mounted, 19" wide and 1 3/4" high, telephone interface that compliments the remote broadcast telephones to get the most from ordinary dial-up telephone lines. Has low and high frequency equalizer controls. Works very well for on-air talk shows and for recording audio in production studios.      

Technical Specifications:   

The ZH-2 Telephone Hybrid will accept mix-minus (send) audio input levels from -42 DBM to +20 DBM on an active balanced/unbalanced input.  Audio output is also active balanced and is adjustable from zero to +20 DBM at clipping.  Caller frequency response is 300 Hz to 3 KHz +/- 1.0 DB.  The front panel low and high frequency equalizers offer +/- 8 DB at 300 HZ and 3 KHz to make the caller sound more natural.  Audio distortion is 0.2% or less and noise is at -80DBM.    Trans-hybrid null is 10 to 25 DB depending on the telephone line.  A receive filter improves recovered audio signal to noise.  The filter response is -24 DB at 60 Hz, -9 DB at 100 Hz, and -35 DB at 10 KHz as referenced to 1 KHz.


This is an analog product.  It connects to a telephone line either with an internal high-quality line transformer, or with a capacitor in series with that transformer.  This capacitor is also internal.  These two configurations allow the hybrid to terminate and hold a telephone line or bridge onto a line, which might be held by another device like a telephone.  Connections are made via a screw terminal strip at the rear of the hybrid. 

There is a "conference" feature, which was put in the original design, to allow two hybrids to conference/exchange audio between two telephone lines.  However, it does not work as well as expected so it is not recommended that hybrids be connected in this manner. 

Schematics in .pdf:  Main Page  Ducking Circuit add-on  The Ducking Circuit is included in all hybrids sold nowadays.  February 15, 2017 update:  The threshold point of the ducking circuit can be desensitized by 11 dB when a 1 meg ohm/1/4 watt resistor is added in parallel with R1, a 3.3 meg ohm resistor, on the Ducking Circuit board.  This will decrease the chance of accidental caller gain reduction when there is room noise in a broadcast studio while the announcer's microphone is turned on. 


The Zercom ZH-2 Telephone Hybrid carries a one-year parts and labor warranty.  If you get a unit and decide it is not right for your situation, you may return it for refund, minus the shipping costs, within 30 days of purchase.  A refund assumes the unit has not been damaged or modified in any way.    

        $199.00 plus shipping and tax.

   Questions?  Email Mark Persons:  teki@mwpersons.com        

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page last edited 02/15/2017