Turn HT into a "mobile" radio via battery contacts?

norcalscan · Mar 17, 2016

I have some UHF Tait handhelds that have no external power solution to them other than charging. The charging circuits don't provide power for transmitting. There are times we need to adapt the handheld to "mobile" aircraft solution since the pilot can't use a "literal" hand held radio and fly at the same time, and a battery just doesn't cut it for large jobs (and pilots can barely remember their lunch let alone managing batteries.)

An idea I had was to rip out the guts of a battery pack and simply use the shell to externally apply the proper voltage and current to the leads in the shell that contact the radio. I've seen other radio manufacturers do this but not sure if I'm missing something like filtering etc. (which we can do on the incoming power if needed). An example I'm talking about is Battery Eliminator for KG-UV9D [BTE-9] - $15.99

Edit: I'm seeing names for these like Battery Eliminators or Dummy Batteries.

ka4gfy · Mar 17, 2016

I would be real careful about installing another radio in aircraft. Using the aircraft electrical system will require an avionics technician with a GROL to OK it and possibly an A&P mechanic will have to sign off on it as well.

Doing anything in an aircraft outside the norm gets real messy and FAA has a low tolerance to these things.

My flying club had to have the entire weight and balance done on both airplanes when we upgraded the radios. An avionics tech had to certify the install and an A&P had to certify the new weight and balance.

73,
Rich, KA4GFY

mmckenna · Mar 17, 2016

norcalscan said:
I have some UHF Tait handhelds that have no external power solution to them other than charging. The charging circuits don't provide power for transmitting. There are times we need to adapt the handheld to "mobile" aircraft solution since the pilot can't use a "literal" hand held radio and fly at the same time, and a battery just doesn't cut it for large jobs (and pilots can barely remember their lunch let alone managing batteries.)

An idea I had was to rip out the guts of a battery pack and simply use the shell to externally apply the proper voltage and current to the leads in the shell that contact the radio. I've seen other radio manufacturers do this but not sure if I'm missing something like filtering etc. (which we can do on the incoming power if needed). An example I'm talking about is Battery Eliminator for KG-UV9D [BTE-9] - $15.99

Edit: I'm seeing names for these like Battery Eliminators or Dummy Batteries.

Aircraft issue aside, Yes, this can be done.

However, you need to look at the specific radio and design accordingly. Supplying 13.8vdc to the battery contacts on a radio that is expecting to see 7.5vdc is not a good idea. You'll need a voltage regulator somewhere along the line to bring the voltage down to what the radio wants to see. This is pretty easy, but the voltage regulator needs to be designed for the amount of current the radio will pull as well as a way to dissipate the heat. This -might- be able to be done inside the old battery housing, or you might want to do it in an external box with heat sink.

N4GIX · Mar 17, 2016

One alternative to having to have multiple sign offs done would be to use a relatively light weight gel cell battery supplying the Tait.

This would remove the issue of being tied into the aircraft's electrical system. The bonus is that this radio could also serve in an emergency situation...

RFI-EMI-GUY · Mar 17, 2016

A comment on battery eliminators and electromagnetic compatibility (EMC).

I have a 6-7 year old Garmin Nuvi GPS in my car. Recently I was using it and transmitting on my UHF SABER GMRS portable at the same time. I started hearing a strange beep. Turns out the cigar lighter power adapter for the Garmin was shutting down (or possible overvoltage) the power to the Garmin.

When using a handheld in a vehicle or aircraft environment, you open yourself up to a bunch of possible EMC problems.

I would avoid making a permanent install of this radio until you have a proper authority like a GROL AP Tech properly install a radio and antenna.

Project25_MASTR · Mar 17, 2016

Try setting the pilot's HT to low power to increase battery life. I know plenty of pilots who run 1W in the air on portables and have QSO'S 100+ miles.

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norcalscan · Mar 18, 2016

Thanks for the avtech concerns, that's all being met. These are temporary radios that we want to adapt to our existing "temporary radio interface" with our aircraft. We have Aux power and external antenna connections available for temporary radios that a client may need such as law, fire, utility, etc. This would tie right into that system. I've got a clean separated 12vdc supply from the 28vdc avionics side that helps feed aux power for temporary devices, GPS and some old secondary AM comm radios.

I did find some 12vdc to 7.5vdc 5A regulators that might fit in the emptied shell of a battery pack. We'll start with that and work from there. We should be drawing about 1.4 amps on high power so hopefully we have plenty of headroom for heat but will keep an eye on that. Unfortunately we do not have access to the programming of these radios so cannot switch from high to low power. I know a lot of this is a people problem and not a technical problem (charge your @$!@ radios!!) but we've got to work around that. Having an external larger gel cell battery to negate some of the people problem still brings me to square one, there is no method of bringing in external DC source to this HT, other than the battery contacts. You'd think a $1500 radio would have that "feature".

Thanks everyone! I'll follow up with what I find or engineer.

cmdrwill · Mar 18, 2016

norcalscan said:
snip/ I did find some 12vdc to 7.5vdc 5A regulators that might fit in the emptied shell of a battery pack.
Thanks everyone! I'll follow up with what I find or engineer.

Just make sure you have the proper 'filter' capacitors on the input and output of the regulator. Check the mfg specsheet. The regulator can oscillate at RF frequencies. We use the three pin TO 220 style regulators mounted on a little flat piece of alum for a heatsink. They are actually a integrated circuit, IC.

Most handheld radios do not draw any more than 2 amps at high power.

Project25_MASTR · Mar 18, 2016

Could always request tait make a convertacom for them…

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norcalscan · Mar 21, 2016

cmdrwill said:
Just make sure you have the proper 'filter' capacitors on the input and output of the regulator. Check the mfg specsheet. The regulator can oscillate at RF frequencies. We use the three pin TO 220 style regulators mounted on a little flat piece of alum for a heatsink. They are actually a integrated circuit, IC.

Most handheld radios do not draw any more than 2 amps at high power.

Thanks cmdrwill. Not sure if the turnkey solution I got has the caps on input and output but will check on that. We'll see how "turnkey" it is. I'm also looking at 3pin TO220 regulators and found a couple that might work - and even take in the 28vdc straight from the copter instead of being behind the 12v converter. With those I do see the schematics requiring the caps and will design accordingly, thanks for the heads up.

This will certainly be behind their own circuit breakers so if the regulator spews noise on a critical freq we can isolate that circuit to kill it. Of course as we design these we'll test them hard against the comm side and FM radios before we give them our blessing. Of course we just tell the pilots if they want to see if the Low Engine RPM warning light works to just push the PTT (push to test). Kidding. Seriously....maybe....

I appreciate the input everyone! It's nice to bounce some ideas off others and make sure my mind is on the right track.

cmdrwill · Mar 21, 2016

norcalscan said:
Thanks cmdrwill. for the heads up..

Glad I can help,

Project25_MASTR · Mar 23, 2016

Boom, already available from Power Products.

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norcalscan · Mar 23, 2016

Thanks W5PKY - we have some of those and unfortunately they do not behave well when using and transmitting the radio while charging. The radios can sit and monitor traffic while charging, but as soon as you transmit the charger gets overloaded. It only provides 700ma of power for the charging and it and the battery freaks out when it's trying to charge and suddenly the load jumps up to 1.5A.

I appreciate you looking. I have exhausted most of my google-fu on this.

Project25_MASTR · Mar 24, 2016

norcalscan said:
Thanks W5PKY - we have some of those and unfortunately they do not behave well when using and transmitting the radio while charging. The radios can sit and monitor traffic while charging, but as soon as you transmit the charger gets overloaded. It only provides 700ma of power for the charging and it and the battery freaks out when it's trying to charge and suddenly the load jumps up to 1.5A.

I appreciate you looking. I have exhausted most of my google-fu on this.

So I actually talked to Power Products about that, they said give them a call. They should not be doing that (even the first gen, current is second gen).

cmdrwill · Mar 24, 2016

norcalscan said:
Thanks W5PKY - we have some of those and unfortunately they do not behave well when using and transmitting the radio while charging. The radios can sit and monitor traffic while charging, but as soon as you transmit the charger gets overloaded. It only provides 700ma of power for the charging and it and the battery freaks out when it's trying to charge and suddenly the load jumps up to 1.5A.

I appreciate you looking. I have exhausted most of my google-fu on this.

Transmitter RF feeding back into the charger, maybe?

Turn HT into a "mobile" radio via battery contacts?

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