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eHam Forums => VHF / UHF => Topic started by: LETTERX on August 31, 2010, 11:03:40 AM



Title: Highest power HT?
Post by: LETTERX on August 31, 2010, 11:03:40 AM
Was a VHF or UHF HT ever been produced that has an output power of more than about 5 watts?  Is there any reason why a handheld radio couldn't be made with an output of say 25W?  It wouldn't obviously have a shorter battery life, and be a bit larger/heavier, but heat dissipation should be manageable, I think.  Has anyone ever modified an HT to have significantly higher output power?

This is something I've been wondering about.  Seems that handheld VHF/UHF radios of all kinds - ham, business, marine, recreation - they all have a maximum output of around 5 watts, and I'm just wondering if there's a reason why that is.


Title: RE: Highest power HT?
Post by: KG4RUL on August 31, 2010, 11:46:32 AM
Why not 25W?

  • * Weight - Probably 5# or more to have decent battery life
  • * Heat - My Wife's VX-5R gets uncomfortably hot at 5W
  • * Size - Gonna need a big hand or pocket

As far as what IS available, the iCOM IC-V85 at 7W is probably King-of-the-Hill.


Title: RE: Highest power HT?
Post by: LETTERX on August 31, 2010, 12:47:29 PM
Okay, yeah, makes sense.  I was thinking of a high-power mode that could be switched on and used briefly just to get a message heard, so heat and battery life wouldn't really be an issue.  Seems like a handheld like this would be ideal for emergency situations in RF-difficult locations (under a building, in a tunnel, between mountains, etc.).  Perhaps it could be activated by a second, small PTT button on the other side of the radio, so you have squeeze them both for the high-power emergency "punch" mode.

I was thinking another amp stage based on a 25W Mosfet.  Couldn't that be made pretty small, even with a tiny heatsink?  Like I said, sort of a high-power emergency mode.  Maybe limited to a 10-second TX, or something like that.  You obviously wouldn't want to chew the fat on a small 25W handheld without an oven mitt.

Maybe there's no commercial demand for a radio like this, but is it possible?


Title: RE: Highest power HT?
Post by: AA4PB on August 31, 2010, 01:08:35 PM
The mfgs probably wouldn't like a high power emergency mode because it would have to have a limited duty cycle. People would be cooking them and sending them back expecting warranty repair  :'(

The other option I guess would be an internal temp sensor that would force it to low power until it cooled off  ;D  but then you'd have those who didn't understand why the HT lost contact after 60 seconds   ???



Title: RE: Highest power HT?
Post by: K5LXP on August 31, 2010, 02:20:27 PM
Technically there's no reason you couldn't build one, but at powers above 5 watts there is an RF exposure safety hazard with an antenna that close to ones' body.


Mark K5LXP
Albuquerque, NM



Title: RE: Highest power HT?
Post by: LETTERX on August 31, 2010, 05:28:07 PM
True, but the RF field strength decreases exponentially (proportional to the cube of the distance?).  So, I could be wrong about this, but I have a feeling there's more of a potential health risk from people literally touching cell phone antennas emitting 2 watts @ 850-900 MHz, and/or 1W @ 1800-1900 MHz.


Title: RE: Highest power HT?
Post by: K5LXP on August 31, 2010, 07:52:33 PM
Well, the question was why you don't see >5W handhelds, and the answer is exposure hazard, one, and at 5W you reach a practical limit of size and practicality.  A rough guess is that 25W into a 0dBi antenna puts the safe range at about 3 feet away.  Not to mention the size of the battery you'd need for the ~75W or so power draw on a battery at that output level.  That's an awful heavy box to be holding out at arm's length.

As to the notion of what's "safe" or not is a separate question, but part of the responsibility of a license holder is to do a station audit for RF exposure levels and certify that they're safe.

Wouldn't take a lot to strap a gel cell onto a 25W mobile and carry it around for a while if you'd like to get a feel for how that kind of setup works.  Not sure where you'd put the belt clip though.


Mark K5LXP
Albuquerque, NM


Title: RE: Highest power HT?
Post by: LETTERX on August 31, 2010, 08:23:11 PM
Wouldn't take a lot to strap a gel cell onto a 25W mobile and carry it around for a while if you'd like to get a feel for how that kind of setup works. 

That's interesting, because I was thinking that the amp stage alone of a 25W mobile rig isn't all that big, and could be reduced in size further with different packaging to better fit a handheld chassis.  I see your point about the battery, though.  I guess a battery-powered amp with BNC connectors to fit on top of an HT is out of the question. <grin>


Title: RE: Highest power HT?
Post by: WB2WIK on September 01, 2010, 09:24:58 AM
True, but the RF field strength decreases exponentially (proportional to the cube of the distance?).  So, I could be wrong about this, but I have a feeling there's more of a potential health risk from people literally touching cell phone antennas emitting 2 watts @ 850-900 MHz, and/or 1W @ 1800-1900 MHz.

There's a lot more to it than that.  These phones only use the power required to hold the circuit and although GSM is 2Wpk and CDMA is usually 1Wpk, these are peak, low duty-cycle ratings.  Average powers run in the 30-300mW range, and the antennas are in the -6 to -10 dBi range, further reducing effective radiated power.

VHF/UHF hand helds that hams use are generally analog FM with a 100% duty cycle for transmission, and the antennas are in the -3 dBi range.

The Specific Absorption Rates are based on effective radiated power, frequency, proximity and duty cycle.

Below is a listing of all the people who have become sick due to the use of hand held cellular telephones:






Title: RE: Highest power HT?
Post by: AA4PB on September 01, 2010, 10:13:06 AM
Given that the HT is less than 50W PEP output and given that it uses push-to-talk, here is what the FCC requires you to do:


Title: RE: Highest power HT?
Post by: KG4RUL on September 01, 2010, 12:06:33 PM
Given that the HT is less than 50W PEP output and given that it uses push-to-talk, here is what the FCC requires you to do:


Patiently waiting for the other shoe to drop  ::)


Title: RE: Highest power HT?
Post by: WB2WIK on September 01, 2010, 02:08:33 PM
Given that the HT is less than 50W PEP output and given that it uses push-to-talk, here is what the FCC requires you to do:


They require you to stare at a white space? :D


Title: RE: Highest power HT?
Post by: AA4PB on September 01, 2010, 03:37:11 PM
Given that the HT is less than 50W PEP output and given that it uses push-to-talk, here is what the FCC requires you to do:


Answer: Nothing. Radios under 50W PEP and mobile/portable stations using PTT control are exempted from the RF exposure requirements.


Title: RE: Highest power HT?
Post by: KC8WUC on September 02, 2010, 04:58:47 AM
Icom has made and continues to make a 7w VHF HT- the ICV82 and predecessor, the V85.  I've owned the V85  (I forget the exact nomenclature/model),  which put out a considerably strong signal that seemed to reach well beyond what would be expected of a HT (in excess of 50 miles from the third story of my home).  This radio did have a significant downside, the weight of battery and heat generated from operating made talking on this for more than a minute or two less than comfortable.  I imagine that I also received a fair amount of RF radiation as well. 

I've since given up on using HTs and have restricted my operations to remote mounted mobile (marine) and desk top base stations.

73,

Michael  KC8WUC/WDE9344

Toulon, France


Title: RE: Highest power HT?
Post by: LETTERX on September 02, 2010, 05:30:02 AM
I understand Icom makes some 7W HT models, but the effective gain between 5W and 7W is really negligible, and it's why I said "about" 5W in the original post.  I still think a modern 25W Mosfet-based HT is do-able, and could be made about the same size as the average business hand-held of 25 years ago.  You know, those old low-VHF Motorola talkies that police used to have clipped to their belts in the 80's.  When I was a kid, our local police department operated on 39.020 MHz, and their radios were about the size of a small red building brick.  Probably weighed the same, too, with half of that weight being the NiCad pack.


Title: RE: Highest power HT?
Post by: AA4PB on September 02, 2010, 05:36:07 AM
In most cases you'll get more "effective gain" by replacing the typical rubber duck antenna with something better than you will by going from 7W to 25W - and it will receive better too.


Title: RE: Highest power HT?
Post by: K7RBW on September 02, 2010, 06:24:29 AM
I'm sure one could be built, but I'm guessing the market for such a monster would be very small.

I have a Kenwood TM-271a Mobile which is a simple moble and is 80% heat sink. I could imagine it to be reformatted into something the size of a very large handheld (e.g. some of those old CB radios) and weigh about 2 pounds (before battery). A 25W out, it'll probably draw 4-5 amps during transmit so, even if you only used "Super-Hi" power occassionally, you'd still need a battery pack that would survive high current draws, even if only momentarily. So, your looking at something like a LiPo technology (like what is used by Electric RC cars and helis), which is expensive. And even if you said "25W for emergency only," some (most) would complain that it wouldn't be worthwhile unless you could do it for a while, which means a bigger battery.

So, while none of this is rocket science, you end up with a heavy and expensive brick hanging from your belt or harness.

Now, with VHF, the antenna placement is much more important than the raw power out, so I'm thinking that 25 watts into a (beefed up rubber duck) held up to your head or hanging from your waist isn't going to go much further than 5 watts. If you are going to put an external antenna on the radio to take advantage of the power, then you're might as well use a mobile radio hooked to an external battery. Or, just put a better antenna on your existing 5W handheld (I've made 80-mile QSOs from a handheld into a good mobile antenna.

So, I'm sure you could make a 25W handheld, but why bother?

--Bob
K7RBW


Title: RE: Highest power HT?
Post by: KI4SDY on September 02, 2010, 07:04:52 AM
Having carried those brick radios and all the other law enforcement gear, I can tell you that not only did weight you down when running after suspects, but many officers ended up with curved spines in the direction of the greatest weight. In my case, I tried to balance the radio and other stuff out with a S&W .44 Magnum. Unfortunately, my spine curved in the direction of the S&W and has stayed there ever since.  :(


Title: RE: Highest power HT?
Post by: AA4PB on September 02, 2010, 01:25:59 PM
Many of the new mobile radios are getting pretty small. Why not put one in a back pack along with an appropriate battery and antenna?


Title: RE: Highest power HT?
Post by: W3LK on September 03, 2010, 02:06:34 PM
I understand Icom makes some 7W HT models, but the effective gain between 5W and 7W is really negligible, and it's why I said "about" 5W in the original post.  I still think a modern 25W Mosfet-based HT is do-able, and could be made about the same size as the average business hand-held of 25 years ago.  You know, those old low-VHF Motorola talkies that police used to have clipped to their belts in the 80's.  When I was a kid, our local police department operated on 39.020 MHz, and their radios were about the size of a small red building brick.  Probably weighed the same, too, with half of that weight being the NiCad pack.

With the other half being the frame everything was mounted inside. :)

I've seen more than one of those that had been run over by a vehicle with no noticeable damage OR decrease in performance. I'm also familiar with a couple of incidents where they became a "non-lethal" alternative with a baton wasn't available. :)


Title: RE: Highest power HT?
Post by: W4KVW on September 04, 2010, 09:05:04 AM
You can do it! Just buy a HIGH POWER dual band mobile & a deep cycle marine battery & head out.That is why it is NOT possible today.The BATTERY or POWER source would be the issue,NOT the radio! Hope you have a GOOD BACK! }:>)

Clayton
W4KVW ;D


Title: RE: Highest power HT?
Post by: KE3WD on September 04, 2010, 05:29:14 PM
I once hopped up the output of one of those old Motorola HT's that had been converted for 2 meter use.  Got about twelve  watts, measured into the shop dummy load on the Bird. 

However, the doggone thing would give you these funny headaches when attempting to use it in QSO for more than a few seconds.  I wasn't the only one who complained of that, either. 

It hurt the eyeballs, no kidding. 

Battery life was rather short when on the high power setting, even with extended packs. 

But that eyeball thing was the reason for abandoning that notion.

The damn thing could make ya nauseous. 



Title: RE: Highest power HT?
Post by: KB1GMX on September 08, 2010, 07:38:56 PM
25W portable..

Find a good used HTX252, that a RS 25W mobile thats just plain tiny.

Add a antenna. you have to find on that can stand 25W.

Battery, 7AH gell cell, net weight 4.6 pounds!  RX operating like about
6 hours, TX full power 20 minutes total (maybe less).

Find a way to get the RF out of the MIC as it will be impossible to keep
far from the antenna.

And since the usual limiting factor is antenna height and antenna quality
you range for that kluge will be only slightly better than a good 5W HT
with a ground plane on a 12ft collapsible fish pole.

A rubber duck has negative gain. One of the 15" jobs will be better
and they do make longer ones!

I've demonstrated a RS HTS245 dual bander a whopping 1.5W using a
39" tall end fed halfwave (ARRL, mobile manual and antenna compendium)
for repeater contacts out to 12-15miles.     If I strap that antenna to a
12ft fish pole (breem or crappy collapsible) the range is even better.   At
VHF it's height and since good antennas are still moderately small that helps.


Allison



Title: RE: Highest power HT?
Post by: VE3ZXK on October 01, 2010, 08:18:32 PM
Why not use a 1W, 50-pound linear in your car? Or a big antenna fed to a deaf receiver?

As you will learn about communications, your most effective gains are in antenna system and antenna height, especially on VHF/UHF.

Many public-safety organizations use in-vehicle UHF/VHF crossband repeaters, which any ham can use if their licence permits.

I don't know what the point of a 25W portable would be. Perhaps you could be heard, but often you couldn't hear, especially within a building with a crummy rubber duck.

You would be much better focusing on how to improve your antenna situation than to worry about output power. I have been amazed at how well a ground 1/4 wave counterpoise will work on an HT. It looks goofy, but greatly improves performance. A telescopic 1/4 wave works great for an HT too. Isn't there a legal requirement to use the minimum power possible to maintain a radio contact?


Title: RE: Highest power HT?
Post by: K2OWK on October 03, 2010, 01:13:06 PM
Hello, Watts the problem. $119.00 gets a Mirage HT amp for 2 meters that puts out 35 watts. Works on FM and SSB.  It works from 12 volts and has an RF receive amp as well. Hook up a 12 volt gel-cell make a carry holder for the amp and the battery and your set to go. I do not see any reason for this much power on 2 meters or 70 cm. My HT will hit just about any repeater I can hear, and that's why I bought it. If I need a high power system I would buy a Mobil 100 watt VHF/UHF portable.

Just a note, If you want you can buy a 25 watt high frequency amplifier on an IC for not to much money. We used them many years ago on a navigation beacon on 421/441 MHz. Never had a problem with them, and the circuit wiring  is minimal. One of the joys of Ham radio is the ability to experiment. Lay out a 25 watt hand held circuit and see what you can come up with. Might even be marketable who knows.

73s
K2OWK


Title: RE: Highest power HT?
Post by: KC9PWT on October 04, 2010, 09:04:31 AM
i took the proposal and made up a bag radio  with a yaesu ht a 50 w amp and a large gell cell, the ht can operate on internal batteries, external batteries, with it own antenna or the antenna attached to the bag, i can remove the ht to work on it own, it also has some jumpers and a cigarette lighter plug that will power the system from an auto battery , the antenna attached will attach to an auto window so i can adapt it to any car or truck, so this can be down, it weighs about 10 lbs all together but is portable enough and powerfull enoughh to reah some diatant repeaters.  i used an army butt pavck and shoulder strap to carry the whole  deal.

alex

kc9pwt


Title: RE: Highest power HT?
Post by: KQ6Q on October 17, 2010, 07:15:07 PM
If the 5W setting on your HT isn't getting heard where you need to be heard, you either change your location (get out of the building, or out of the gully) to where your signal isn't being blocked, or use a more efficient antenna - if you're using the stock 'duck' that came with the radio, get a better aftermarket antenna (it WILL be a lot longer than the 'duck'), use a counterpoise with the duck or other antenna, or use something like a Jpole or an lightweight beam (ELK and Arrow make some) and a painter's pole or tripod setup to get it up into the air.
If you've ever used an HT extensively on the 5W setting, you'll know that it gets quite hot.  You'd need barbecue mittens to hold onto a 25W HT.  If you regularly operate from inside a building, and have trouble getting a signal out, consider putting an outside antenna on the building, if that's feasible and allowed. Work with the building maintenance people to run the coax properly.

Fred Wagner, KQ6Q


Title: RE: Highest power HT?
Post by: W6RMK on October 19, 2010, 09:35:21 PM
"Answer: Nothing. Radios under 50W PEP and mobile/portable stations using PTT control are exempted from the RF exposure requirements."

not precisely true. You're still legally obligated to do the analysis, etc., but being in certain power and operating ranges makes the analysis simple, because you can use the "safe harbor" sort of approximations. But you'd still have to document that you met the assumptions.

Watch out for the "multiple transmitter" rule though.  A HT and a cell phone make for multiple transmitters, with both transmitters being greater than 5% of the total power.

I'd not want to get into an argument with a regulatory agency about it.