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VHF 174-215


jwill

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  • 1 month later...

I have used some Lectrosonics 185 systems regularly over the years, not so much recently.  They generally did the job but had some drawbacks.  Some of the drawbacks are inherent in the frequency band, others would depend on the specific equipment.  Another limitation was related to FCC regulations of the time that have recently been amended to improve things.

 

Inherent in the band:

1) Low frequency means large antennas.  For receive antennas we had large Yagi antennas installed in one location and used coax whips other places.  The Yagis were reliable, the whips less so.  On the transmitter side, however, the microphone cable shield was the RF antenna, and so care had to be taken that the cable stayed relatively long and straight for best performance.  This is probably a reason much of the VHF use today is IFB or similar.

 

Specific equipment:

2) Most systems were fixed frequency.  Not as flexible for avoiding other users, but on the upside, it did allow the RF design to incorporate tighter filtering which was good for performance.

3) No diversity.  I'm not sure how big a problem this really was, but it did seem that we'd have places with nulls and I expect diversity would have helped.

 

Regulation:

4) VHF systems were (and still are to some degree, I believe) limited to a handful of specific channels.  Originally, the allowed frequencies had been chosen without much (any?) regard to intermodulation in multichannel systems.  Regulation changes that took effect with the 600MHz auction introduced a new coordinated frequency set that is better for operating more systems simultaneously.

 

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