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Categories | QRP Accessories | W4RT Electronics Help

Show all reviews of the W4RT Electronics

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G8JNJ  Rating: 4/5 Sep 14, 2007 03:24  Send this review to a friend!
Works OK - but not for me  Time owned: 0 to 3 months
W4RT OBP Dual Element Module – OBP with Heil HC-4 & HC-5 mic capsules.

I bought this unit directly from W4RT (as the UK dealers were charging twice the US price). In order to try and improve the quality of audio, and boost the talk power of my FT-897D.

The unit arrived in good condition and I installed it without any problems into the Yaesu MH-31 (stock microphone with the FT-897). The unit has two Heil mic inserts the HC-5, for local contacts, and the HC-4 which provides a 2.5KHz boost for DX working. The modification to the microphone uses the existing ‘tone’ switch on the back of the microphone to switch between the HC-4 and HC-5 microphone inserts, but the OBP compressor is only used in the HC-4 position.

The module works well, but did not solve my problems. The muffled audio was still present (mainly in th HC-5 position)and the average output power didn’t increase significantly.

I investigated both these problems, and concluded that the muffled audio was actually due to the case design of the MH-31 microphone. This uses horizontal ‘vents’ which cover the holes in the front of the Heil elements as they don’t quite line up with the gaps correctly.

The very limited improvement in average audio level obtained when using the OBP compressor is due to the ALC action of the radio. If you increase the average audio level the ALC winds the output power down to compensate. You can read more about this issue at:-

My only minor criticism of the module, is that with my voice, there was a large difference in output level between the HC-5 and HC-4 with OBP and I had to change the mic gain each time I switched between the two.

I eventually solved my problems by using an electret mic and using the internal 'processor' option correctly.
Product is not in production.
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