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Author Topic: Why are all HT 5watt or less?  (Read 9657 times)
LB5KE
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Posts: 141




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« on: November 18, 2011, 04:42:55 PM »

Never seen one above 5w
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AA4PB
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Posts: 12638




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« Reply #1 on: November 18, 2011, 04:51:50 PM »

Battery life, heat, and size. In addition, to get 3dB improvement you'd have to go to 10W. For 6dB - 20W, and for 9dB - 40W.
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WB6BYU
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« Reply #2 on: November 18, 2011, 06:12:28 PM »

I've seen an occasional one that advertises 6 watts.

One issue is concern about the safety of holding such a transmitter beside your head.
You can use the FCC RX Exposure Guidelines and see what the recommended distance
is for higher powers.

But the main issue is practicality:  a HT has to be small, which means a small battery
with limited capacity.  The higher the power, the less operating time you get.  You
gain far more by improving the antenna on the radio than by running higher power.

And, at some point you need a bigger heatsink.  Many of the small HTs get too hot
to hold comfortably after extended operation at high power.


My approach has been to improve my antenna until I can carry on the desired
communication on the low power setting.  That gives me more operating time.
Only if that isn't good enough do I resort to high power.
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K1CJS
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« Reply #3 on: November 19, 2011, 05:30:34 AM »

The Icom 2GAT was listed at 7 watts, but QST measured it doing 8.5 watts!  Icom has 3 other HTs rated at 7 watts-the 2GXAT (great HT), the V82 and the V85.

Icom has several HTs that will do 7 watts--IF--they're used with an external 12 volt source.  BYU has the reasons right, chief of which is the battery power.  You can't have to recharge your handheld battery after every conversation.  That handheld wouldn't be too practical if you did!

Also to note is that those handhelds that can do over 5 watts usually have a temperature controlled foldback on power output to save the finals from destroying themselves by overheating.  Most of those handhelds won't transmit more than a minute or two at higher power before they would get too hot to handle.  The Icom T7H that I have does have that power foldback, and it can get mighty warm fast.  Most other handhelds can also, and probably have the foldback feature as well.
« Last Edit: November 19, 2011, 05:34:45 AM by K1CJS » Logged
KE4YOG
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Posts: 182




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« Reply #4 on: November 19, 2011, 05:37:01 AM »

The old Radio Shack 202 did betwee 7-9 watts when power by external 12 volt supply. It was around 5 watts on battery. I used on for a good amount of time with the 2 meter amplifier that Radio Shack had during that time. I worked for them at the time. We had a special promotion by which the employees could get a discount equal to the sales gain for the same month the previous year. We did a 29 perent gain. I bought the 202 and amp.
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KM3F
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Posts: 494




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« Reply #5 on: November 19, 2011, 09:52:39 AM »

John is correct. At those power levels the radio has no real heat sink to get rid of the heat.
The old 202 HT would get to hot used as a base and rag chewing on a repeater for very long.
For  a battery pack to last very long under those power levels would be bigger than the HT.
The old 202 size was half batteries as it was.
Even many mobile radios for vhf fm are not to be used to long on their high power setting due to overheating.
I hear ops using HT in the car for extended periods and wonder if the radio is really getting to hot powered from the car. If they are using a hand mike doing it, they may not even be awhere of it.
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WB2WIK
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« Reply #6 on: November 19, 2011, 12:36:57 PM »

All good answers.

HTs aren't designed for anything remotely close to continuous duty and the 5-7W models get very hot if you transmit for 2-3 minutes.  They're mostly designed for 1 minute of transmitting with a 1-2 minute cool off period.

To make a higher power hand held takes bigger batteries, bigger heat sinks: Resulting in a large, heavy "hand held" that probably can't really be held in your hand.

Hand helds are designed for field use, with either very limited range simplex or extended range via repeaters, in which case the repeater does all the work so the HT doesn't have to be so great nor powerful.

I can "hit" repeaters here, sitting on my living room sofa, that are 70 miles away, just using a 3W hand held with its rubber flex whip antenna.  In such case, the repeater is up 6000' high or more and I'm pretty much line of sight to it, other than the walls of my house.

In places where there aren't 6000-8000-10000 foot mountains with good repeaters on them, it's hard to do that. Wink
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KQ6EA
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« Reply #7 on: November 19, 2011, 01:27:08 PM »

A 202 is "half batteries"?
I don't think so. The entire radio is about 6-1/2" long, and the battery is about 2-1/4".
More like one-third, but definitely NOT "one half"!
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LB5KE
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Posts: 141




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« Reply #8 on: November 20, 2011, 04:20:07 PM »

Modern batteries has twice the capacity of batteries 8-9 years ago. And regarding heat, isn't that solvable with class-c amplifiers etc?
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W8JX
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Posts: 5319




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« Reply #9 on: November 20, 2011, 04:42:05 PM »

Modern batteries has twice the capacity of batteries 8-9 years ago. And regarding heat, isn't that solvable with class-c amplifiers etc?

 And modern HTs tend to use more power too because efficiency has not improved. Generally figure to make 5 watts out you will consume close to 15 watts to power HT and finals. Talking short battery life unless it is a big brick and them HT is smaller and smaller with trend to LESS battery to keep it small and then less area to dissipate heat from finals too. Could you get 10 watts or more out of a small HT? Yes but it would be a race to see if it overheated or killed battery first. on external power it would have power but not dissipation to live long.
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WB6BYU
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« Reply #10 on: November 20, 2011, 04:46:56 PM »

But radios are physically smaller, too.  Nobody who is used to a standard mobile
phone would want to lug around an IC2AT, TR-2600, or other radios of that
vintage with their heavy batteries - even for just 2 watts output.  (And that
aggravates the problem with high power - there is not as much chassis area
available in the smaller rigs to act as a heat sink.)

All the FM transceivers run class C in the final - there is no reason to do
otherwise.  But at 5 watts output, you still have perhaps 3 watts dissipated
as heat in the final, and somewhat more than that in the rest of the rig.
(The radios that I've modified to adjust the output power still draw about
100mA minimum even with zero output power with the driver stage
shut off.)

So a 5 watt HT is probably drawing around 1 amp from the battery while
dissipating 3+ watts heat.  All that heat gets generated within less than
1 square cm of area, and needs to be dissipated so it doesn't buildup.
To make small and light radios, manufacturers aren't going to add enough
copper or aluminum to dissipate that heat sufficiently for continuous
operation.  

If you need more power than that, rig up a mobile rig with an external
battery in a backpack or shoulder bag.  But make sure you leave enough
room around the heat sink for proper ventilation.
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W8JX
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Posts: 5319




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« Reply #11 on: November 20, 2011, 06:03:50 PM »


So a 5 watt HT is probably drawing around 1 amp from the battery while
dissipating 3+ watts heat.


I would like to see you find a HT that only draws a amp from battery pack at 5 watts out. Example, Kenwood TH F6A draws 2 amps off battery pack at 5 watts out. Modern HT's are smaller but still very inefficient.
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WB6BYU
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Posts: 12974




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« Reply #12 on: November 20, 2011, 06:52:20 PM »

Good point - they are actually worse than I thought.

I pulled out the manual for my TH-D7A and it lists the following output powers and
current draws at various voltages:

High (13.8V external power) gives 6W and draws ~1.6A.
High (9.6V battery) produces 5W and draws the same ~1.6A.
High (6.0V battery) produces 2.5W and draws ~1.3A.
Low (6.0V battery) produces 0.5W and draws 500mA.
Extra-Low (6.0V battery) produces 50mW and draws 300mA.

So running high power on the 6V battery draws 7.8W and gives only 2.5W output.
That's over 5W dissipated elsewhere in the radio.  At the higher voltages the
rig dissipates 10W or more.
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N5RMS
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Posts: 37




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« Reply #13 on: November 25, 2011, 01:08:58 PM »

Look where the antenna is in relation to your eyeball.  RF can cause tissue heating.
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KG4NEL
Member

Posts: 373




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« Reply #14 on: November 28, 2011, 10:10:47 PM »

I remember what the VX-5R was like after a long QSO - that would have caused blistering had it been any more powerful than 5W Cheesy
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