Monday, October 23, 2006

Learn about Crossband Repeating

Adated from an article written by Christian KC0ARF

Crossband Repeating is a process where a Ham transmits one signal on one band (typically UHF), and it is received by another radio with a better antenna/power installation, and re-transmitted (typically on VHF) to another radio system, or a repeater.

When is it a good time to crossband repeat? Anytime that you are using an HT, and cannot be heard into the repeater system, or when you are working an extended event, and do not want to exhaust your HT's batteries.

Types of Crossbanding

There are two types of crossbanding- half duplex and full duplex. Full duplex means that the crossband repeater manages both "sides" of the conversation through to the repeater, whereas half duplex means that only your "side" of the conversation is re-transmitted.

Half Duplex

The easiest setup for crossband repeating is half duplex.

Using half duplex, the HT is set to transmit on a private UHF simplex frequency to the mobile radio. The mobile receives the signal, and re-transmits it into the repeater. When the HT is done transmitting, the mobile radio falls quiet, and the HT hears other people directly from the repeater.

How to setup this scenario:

* Setup your HT to transmit on UHF (let's say 446.00) Do not use that frequency... find your own!
* Setup your HT to receive on 145.13.

* Setup your mobile radio to transmit on 144.53, Do not, in this case, program in 145.13 with a (-) offset. You want the 144.53 simplex in the radio.
* Setup your mobile radio to receive on UHF simplex (our example, 446.00) .

* Place the mobile in crossband repeat. Check the power levels to ensure they are at minimal levels.

Full Duplex

Full duplex crossband repeating is more difficult to setup, but it does work. If your particular situation allows for half duplex, I strongly suggest that you proceed with that setup. Full duplex places many more demands on your crossband repeater, because it will be working almost 100 percent of the time. Remember, it re-transmits all of the data on the repeater, too! Only use this scenario if your HT is in a location that cannot hear the repeater directly, such as in your basement during severe weather.

Thanks to the contributer Christian KC0ARF

Tuesday, October 03, 2006

Lightning Strikes

One of our Ham member had the misfortune of getting his
rig setup hit by a big bolt of Lightning.

From the fotos below, one can see the damage that
lightning can do to your equipment if steps are not taken to
reduce the chances of it being hit by Lightning.

One good way, is to disconnect the aerial feed cable
connector from the rig. This will prevent the Lightning bolt hitting it.
But mind you, you must now take care to prevent the bolt
of Lightning coming down the aerial feed cable and
hitting you in your room!

Its clear that the cable connector has been
detached from the the cable itself.

The cable end is approximately 12 inches
away from its connector!

This Cushcraft Ringo Ranger bow blown into an oval
shape from its original half dipole shape.

The Dexion angle iron mounting to the
wall made a hole in the concrete that
required wall repairs!

Anothe view of the hole in the wall.

Even the telephone incoming line box just "exploded".

Another view of the telephone junction box.

So it pays to take precautions during periods of Lightning activity in your vicinity.

Monday, October 02, 2006

Bukit Lanjan Repeaters

Ever wondered how the VHF and UHF repeaters
look like on Bukit Lanjan?

I had the rare occasion snapping some fotos to
illustrate for the benefit of some new Ham
members how Repeaters look like.

The grey cabinet on the left contains MARTS equipment

Top to bottom:
UHF repeater made by Standard (now YAESU)
Middle left:
AC to DC power supply loaned by 9M2RT which supplies
power to both UHF and VHF repeaters now!
Middle right:
The 2 Motorola Mobile sets working to be a Repeater in
conjuction with a Motorola Interface. One mobile is the
transmitter, the other mobile is the receiver.
The 2 units are sandwiched between 2 wooden planks to keep
them erect!
The 4 antenna Cavities (looks like storage bottles) that has
been tuned for optimizing our transmit frequency.

Close up view of the 4 Cavities

At the moment, both the our repeaters seem to be working
OK, but the Motorola units will return to Penang once our original
VHF repeater is replaced.