Rating portable antennas in system design

[HumHead]

When doing system design modeling, what do people use as a (negative) gain figure for portables?

Thanks!

P.S. Woo Hoo- 1,000 posts!

[Nand]

-6 dBd

Nand.

[Dan562]

Humhead,

"When doing system design modeling, what do people use as a (negative) gain figure for portables?"

If you are system designing you lost me at the Negative Gain Figure for portables. To me, Negative means signal path losses, there is no gain to the portable handheld signal.

Then you want someone to give you the antenna signal losses for a portable handheld unit without telling which frequency band of operation the customer is using? Is it 40MHz, 150MHz, 450MHz or 700/800/900MHz?

What type of antenna will be used 1/4 wave or Heliflex?

How the individual is using the portable handheld, i.e. at head level or worn at waist level on a belt? The human body absorbs X amount of RF signal when using a handheld portable unit and it's different for each band of operation.

I need clearly defined information from you so I can provide a decisive answer.

Dan

[HumHead]

Thanks Dan and Nand.

I will admit that I painted that question with fairly broad strokes.

It is my understanding that, when modeling possible system coverage, portables are generally rated with a negative dBd or dBi gain figure due to the inherent inefficiency of their antenna systems.

I'm actually looking at variations in coverage for VHF-Low (46MHz), VHF-High (155MHz), and UHF (460MHz) in a hilly area using Radio Mobile. I had been using the assumption of a hand-held radio at 1.5m high, with a heliflex antenna. If was using 5w for VHF and 4w for UHF.

For now, I'm working with the default receiver sensitivity of 1microvolt, although I am eventually planning to go out and measure actual site and field numbers.

[N4DES]

If I remember correctly we used -7dB for the Public Safety Speaker mic at 800 MHz. I would have to check my notes at the office to check the exact figure.

Of course we make up the loss with the use of TTA's and the radios without the shoulder mic. even works better.

[Dan562]

Here's what I have for system Portable losses using a Heliflex antenna at head level: 40MHz -17 dBi, 160 MHz -8 dBi and 460 MHz -7 dBi. Now at waist level (worn on the belt) 40 MHz -27 dBi, 160 MHz -17 dBi and 460 MHz -13 dBi. It's rather obvious that using a handheld portable unit at head level has an over whelming advantage.

When I work on RF system coverage, I always like to have a Topographic map of the area available to determine any potentially RF shadowed or dead spots in the system. I always provide the customer a coverage map using access percentage as 90%, 70% & 50%.

Seven years ago I predicted what a coverage area would look like for a Motorola iDEN 900 MHz Alpha system in Ft. Lauderdale and then the Beta system in Las Vegas a few months later. The site manager was amazed of my system coverage predictions ... they were right on money.

Dan