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Hopping from fiction to fact.

There's a love/hate relationship going on with the frequency hopping multiplexer (FHMUX). Some units won't deploy without the FHMUX. Others don't want a thing to do with it!

The reason for the two views is the garbage being churned out by the rumor mill.

Rumor One

We lose range and power when using the FHMUX.

Okay, it's true you don't get the same RF power out of the antenna connector on the front of the FHMUX as you would at the AM-7238 power amplifier.

But, you do get optimum range and that's what you're after! Using multiple active radios and antennas produces less range than using a FHMUX with a single antenna.

Suppose you're using four OE-254/GRC antennas located around your command center. You're going to get interference and "frequency collisions." Down goes the range of your radios. The FHMUX range will be greater with no interference or "collisions"!

Rumor Two

We can only transmit on one radio at a time through the FHMUX.

Not even ah okay, here. This rumor is not true!

You can receive and transmit on all four radios at any time through the FHMUX. The FHMUX switches between radios hundreds of times per second. The switching is so fast you won't know it's happening.

Rumor Three

The FHMUX can only operate for up to 24 hours, then it must be shut down or it will fail.

This is garbage, folks. True, some early FHMUXs had an over-heating problem, but that's ancient history. Now they can operate until the cows come home--and leave again in the morning!

Rumor Four

FHMUX doesn't always work.

If the FHMUX does not work, the problem is probably with the cables. You've connected them wrong! When the repair guys are called in to troubleshoot, that's usually what they find.

Make sure you have the needed FHMUX manuals to get it up and running. You'll need: TM 11-5820-890-10-8, SINCGARS Operator's Manual; TM 11-5820-890-23P, Unit and Direct Support Maintenance Repair Parts and Special Tools List for FHMUX TD-1456/VRC and Mount MT-6845/VRC; SB 11-131-2, Supply Bulletin Vehicular Sets and Authorized Installations, VOL II, SINCGARS, FHMUX, and EPLRS; TM 11-5820-890-30-6, Direct Support Maintenance Instructions for the TD-14 56/VRC Multiplexer.

Rumor Five There is no advantage gained by using the FHMUX.

That's a rumor that is way off base. Using the FHMUX provides several advantages.

1.The FHMUX reduces your visual target signature. Fewer antennas means you're less likely to draw the enemy's attention. That increases your odds of surviving on the battlefield and that's an advantage you definitely want.

2. The FHMUX has improved radio range. The use of the FHMUX and one antenna reduces the interference and frequency collisions that degrade your radio net ranges.

3. The FHMUX reduces setup and takedown time. A unit takes about two hours to erect four OE-254 antennas and about 30 minutes to set up the one OE-254 antenna using the FHMUX.
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Title Annotation:FHMUX TD-1456/VRC ...
Publication:PS, the Preventive Maintenance Monthly
Date:Nov 1, 2003
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