Using ship's antenna for handheld?

[ShuRugal]

Is it possible/legal to use the ship's antenna for a handheld radio?  I would love to wire up my Yaesu FTA-750 (which I carry as an emergency backup).  Right now I only have my GNS-430 for primary comms, I would love to either install an external antenna for the handheld, or multiplex it into the ship's antenna, and pipe the audio output to be com-2 on my GMA340.  I plan to ask my A&Ps the same question at annual next month, but coming armed with knowledge on the subject seemed like a good idea.

[Bolter]

My panel has a phono plug with placard for this purpose.  I have a cable stashed in a seat pocket that goes from phono to BNC that fits in place of the handheld's antenna.  This is my backup's backu, and I like having it there.  

[ShuRugal]

Yes and yes. Look around under your panel for an antenna coax with an open BNC connector. There's a good chance one of your plane's previous owners had the same idea. One of mine did.

I'll talk to the previous owner, then. He's an IA, and he restored this plane in 2007.

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[takair]

Try something like this:

https://www.edmo.com/products/handheld-radios/antenna-switchbox-ic-ant-sb

it is for emergency use.  It switches between the handheld and the installed comm.

[Yetti]

You need a coax splitter and a 50 omh terminator if you don't have that switch thing above. 

Most radios have a pigtail out of the back of them of about 6 inches.   Insert splitter, run coax to accessible location.    The switchy thing may be a good idea so you are not pumping RF from the handheld into the back of the ship'sl radio and frying it.

[EricJ]

Get under the panel and see if you can sort out how the coax for the comm antenna is routed.   As others have said, there may already be a transformer that allows a handheld to be connected, or a joint where the antenna could be disconnected in flight from the GNS and connected to your handheld instead.

It took me a while to figure out what the jack in the pic from my airplane was for, but it's a transformer for an old KX99 handheld that allows it to be plugged in with a pin jack to the COM2 antenna.   I bought a piece of coax with BNC connectors and a BNC-pin fitting and tested the receiver, and it works great.

A question I've had relates to the fact that typical comm receiver input electronics are fairly sensitive and I don't know how well a nav/com com receiver is protected (outside of the internal Tx/Rx switch, which is normally in Rx mode) from excessive input power.   When transmitting with the handheld I'd be worried about potentially damaging the receiver if they're connected via a simple transformer.   I *think* the reason the KX99 transformer uses a pin jack is that it disconnects the in-panel receiver side when the pin is inserted.   I checked this, though, with my in-panel receiver on ATIS I plugged in the jack, and while it did get noticeably weaker it didn't disconnect completely.    I haven't been able to find receiver specs for typical nav/com units that shows max allowed input power.   It could be that there is a lightning spec or something that provides sufficient clamping that it is a non-issue, but without knowing that I'm a bit chicken to try transmitting with the handheld plugged into the transformer unless it's actually needed.   I can also reach right behind the transformer and unplug the antenna cable and plug it directly into the handheld and make it a non-issue, too.

Anyway, that's the sort of thing you're looking for or could install.  The below pic shows my engine instruments with the transformer and jack attached at the bottom of the panel.   Took me a long time to figure out what it was.   The bottom pic is me getting my phone underneath it to get a pic of it to figure out what it was. 

 

[Marauder]

Get under the panel and see if you can sort out how the coax for the comm antenna is routed.   As others have said, there may already be a transformer that allows a handheld to be connected, or a joint where the antenna could be disconnected in flight from the GNS and connected to your handheld instead.
It took me a while to figure out what the jack in the pic from my airplane was for, but it's a transformer for an old KX99 handheld that allows it to be plugged in with a pin jack to the COM2 antenna.   I bought a piece of coax with BNC connectors and a BNC-pin fitting and tested the receiver, and it works great.
A question I've had relates to the fact that typical comm receiver input electronics are fairly sensitive and I don't know how well a nav/com com receiver is protected (outside of the internal Tx/Rx switch, which is normally in Rx mode) from excessive input power.   When transmitting with the handheld I'd be worried about potentially damaging the receiver if they're connected via a simple transformer.   I *think* the reason the KX99 transformer uses a pin jack is that it disconnects the in-panel receiver side when the pin is inserted.   I checked this, though, with my in-panel receiver on ATIS I plugged in the jack, and while it did get noticeably weaker it didn't disconnect completely.    I haven't been able to find receiver specs for typical nav/com units that shows max allowed input power.   It could be that there is a lightning spec or something that provides sufficient clamping that it is a non-issue, but without knowing that I'm a bit chicken to try transmitting with the handheld plugged into the transformer unless it's actually needed.   I can also reach right behind the transformer and unplug the antenna cable and plug it directly into the handheld and make it a non-issue, too.

Anyway, that's the sort of thing you're looking for or could install.  The below pic shows my engine instruments with the transformer and jack attached at the bottom of the panel.   Took me a long time to figure out what it was.   The bottom pic is me getting my phone underneath it to get a pic of it to figure out what it was. 


 

If you ever lose receive & transmit capability for the radio that the KX-99 is attached to, it is that box that is the problem. Mine failed that way. The resistance was extremely high on failure.




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[Schinderhannes]

In my opinion the intended use of a handheld is as a backup when the electrical system fails. Having the ability to connect it to an antenna will be very helpful to improve the performance. I would advise against rigging splitters into the antenna cable of your only (panel mount) radio. Splitters, splices, etc will reduce the performance of your antenna and especially in your case with only one radio this is the last thing you want to do. 

In the last year high quality small size TSOed transceivers (Becker, Dittel, Funke) have become available at prices comparable to handhelds. Cup, Aeronca, Ultralight, etc owners are ditching their handhelds and are installing these radio. No need to buck this trend in an aircraft meant to be a serious traveling machine. If you can free up a standard 2 1/4” cutout install will be easy, keeping cost down. 

And if you should lose your alternator these radios will run on your battery for days. 

[cctsurf]

8 hours ago, Schinderhannes said:

And if you should lose your alternator these radios will run on your battery for days. 

I agree that a second radio normally is a far better way to overcome the issue, however, I do like the idea of using a portable because of the lack of the need for the rest of the electrical system. Another reason to have a separate portable is to avoid using the audio panel, etc. that also may malfunction.  Since getting my license, (actually since my long cross country) I have had far too many problems with my electrical systems to rely on ship's battery as a backup.  I have resorted to my portable twice in two different airplanes when I have had to shut down the master switch for safety reasons.

Having a portable as a backup would prevent having to squawk 7600 for no comms and give an extra level of backup IMC.

I do, however agree that a splitter is a terrible way to do this.  Splitters kill a lot of signal.  If I could recommend something, I would have a coax and a BNC connector available through which say com2 is normally connected and have a cable for the portable that could connect there.  If you HAVE to use a splitter, I would highly recommend connecting a dummy load to the open port when it is not in use.  If there is no dummy load, you actually lose more signal in the splitter than if you have one there.  (I'm an EE, I've done the lab exercises on this)

[Yetti]

Most audio panels have a fail safe 

[cctsurf]

1 hour ago, Yetti said:

Most audio panels have a fail safe

Which helps me how if the radio is wired up to the smoking electrical system for power?

Edited March 16, 2018 by cctsurf
Sorry, too personal.

[Jerry 5TJ]

I installed a third com antenna and keep it connected to the handheld radio. The handheld’s battery charges when the master is on.  

 

[cctsurf]

13 minutes ago, Jerry 5TJ said:

I installed a third com antenna and keep it connected to the handheld radio. The handheld’s battery charges when the master is on.

I guess that would take care of it.  Also remove the desire for a splitter...

[EricJ]

3 hours ago, cctsurf said:

I agree that a second radio normally is a far better way to overcome the issue, however, I do like the idea of using a portable because of the lack of the need for the rest of the electrical system. Another reason to have a separate portable is to avoid using the audio panel, etc. that also may malfunction.  Since getting my license, (actually since my long cross country) I have had far too many problems with my electrical systems to rely on ship's battery as a backup.  I have resorted to my portable twice in two different airplanes when I have had to shut down the master switch for safety reasons.

Having a portable as a backup would prevent having to squawk 7600 for no comms and give an extra level of backup IMC.

I do, however agree that a splitter is a terrible way to do this.  Splitters kill a lot of signal.  If I could recommend something, I would have a coax and a BNC connector available through which say com2 is normally connected and have a cable for the portable that could connect there.  If you HAVE to use a splitter, I would highly recommend connecting a dummy load to the open port when it is not in use.  If there is no dummy load, you actually lose more signal in the splitter than if you have one there.  (I'm an EE, I've done the lab exercises on this)

The other benefit of a handheld is that if you do wind up on the ground off-airport somewhere you can walk around with it and use it outside of the airplane.

A good splitter/transformer that's properly installed shouldn't present much loss in the antenna-nav/com path.   It does present *some* loss compared to a direct connection, so that is a consideration for purists.

I'm really curious as to the internals of the KX99 splitter that I have, since the pin jack theoretically would allow a much more efficient implementation.

I'm an EE, too, and have been working in wireless comm for a few decades.    Much of this stuff is so implementation specific that the experience is not always that useful. 

[Yetti]

31 minutes ago, cctsurf said:

Which helps me how if the radio is wired up to the smoking electrical system for power?

I was under the impression that com panel was a smoking mess,  If you electrical system is letting out the smoke,  that needs to be fixed.

You are probably over thinking this, a couple watt VHF handheld a couple thousand feet up in the air has a pretty darn good line of sight.  I would vote for 20 miles of range or more.

Edited March 16, 2018 by Yetti

[Yetti]

I think these are aircraft approved

https://www.radiotwoway.com/rdd5227a-152-162-mhz-1-4-wave-stainless-antenna?utm_source=google&utm_medium=cpc&adpos=1o5&scid=scplp15709&sc_intid=15709&gclid=Cj0KCQjw1q3VBRCFARIsAPHJXrF3n8gTLGhel8OvYDYKwHrpjjACeV3LXZJ8KZwQpWUt9paYz0_ZNhoaAu1nEALw_wcB

[N601RX]

A 2 way splitter has a path loss of 3db to each port. Essentially your power is cut in half. Your are also directing the output of one radio back into the receiver of the other one at a level much higher than it is designed to handle.  If you don’t want to install a RF switch Run the coax along the bottom of the panel and put a male and female connector in the middle. If you have to use the handheld just disconnect the 2 connectors and connect the  one that goes to the antenna to your handheld. 

[ArtVandelay]

How many here have lost all power and both radios for any other reason?

[N201MKTurbo]

If I lose all my electricity, radios are one of least of my problems.

OMG the autopilot will quit and I'll have to drive.

Ill have to figure out how to get the gear down. 

Navigation is more important than talking.

Thank God for IPads.

If you are IFR you will have no distractions, no reroutes, just fly along in quiet bliss.

Edited March 16, 2018 by N201MKTurbo

[Yetti]

I lost power to comm 2 and the GPS on my first student cross country.  Apparently an A&P decided it would not be important to calculate load.   The "fix" was to up the breaker amps till the owner pitched a fit.   I had a handheld GPS and comm  so we were still redundant

[carusoam]

TJ,

Something simple killed the electrical system in my Mooney...

My M20C lost it’s voltage regulator....  I noticed when the radio lights started flashing (day VFR) as the battery had been discharging without my knowledge.... they began flashing as the voltage drops out the bottom of the useful range...

other simple things... a loose / slipping generator belt can do the same thing...

a modern voltage controller with an led light on the IP would at least give faire warning of the impending challenge...

Best regards,

-a-

[N201MKTurbo]

Way back when I was a new private pilot, I was flying a Tamahawk to KTUS when the radio quit. I landed at KAVQ and called Tucson approach on the phone and told them my problem. They gave me a squawk and a route to fly and cleared me to land before I took off.

[ArtVandelay]

Modern engine monitors will warn you instantly if you lose the alternator. I have enough battery power to last 2 hours if I turn off pitot heat, AP, and 2nd com/nav, that’s with nav and strobe lights still on. I can go 3 hours turning off all lights, turn coordinator, 88 and 210.

And if I get low I can use my cell phone in a pinch.

[EricJ]

On 3/15/2018 at 7:43 PM, Marauder said:

 

If you ever lose receive & transmit capability for the radio that the KX-99 is attached to, it is that box that is the problem. Mine failed that way. The resistance was extremely high on failure.




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Do you still have that?   I'd love to pop it open and see if they used the pin jack insertion to isolate the ports.

Meanwhile, I took a couple cable splitters and put them on my lab bench with a couple of Spectrum Analyzers and a Signal Generator.   I connected the signal generator to one of the split ports to simulate transmitting with a handheld, and measured the power output at the input port (which, presumably, would go to the antenna), and the other output port, (which, presumably, would be connected to the in-panel comm receiver).   The antenna output is ~3dB down from the handheld transmitter, and the in-panel comm port is 20dB down from the handheld transmitter. 

There are things other than typical rf splitters that can be used, but I suspect that's usually what gets plugged in.   If something other than a typical splitter is used, results may vary.

However, assuming a typical splitter is used, connected as above, with a handheld with a 7W output the nav/com would see 70mW (~+18.4dBm) at it's receiver input, which isn't too bad.   That's not out of the realm of expectations for a receiver to be able to handle, especially when it is designed for a reasonably harsh environment that deals with lightning and another transmit antenna a few feet away, etc.

Of course the bad news is that the 3dB+ loss to the antenna port means your 7W handheld is instantly turned into a 3.5W handheld, but for VHF AM LOS voice radio 3dB is really not that much, and the advantage of getting to the outside antenna rather than using the handheld antenna inside the airplane is likely greater than that.

A better method might be to have a junction or a union in the coax that could be easily reached so that you can disconnect the antenna cable from the nav/com and connect it directly to the handheld.   That would give you the full 7W to the external antenna.   3dB isn't that much in this application, but it's 3dB you wouldn't have otherwise and if you're on the fringe of reception it'll be noticeable.   This would also avoid the 3dB loss to the in-panel nav/com with a transformer/splitter in place.

My airplane goes into the shop for an avionics-ectomy next month, and I'm thinking of having them delete the KX99 (whatever it does) and just put a bracket there with a connector that I can reach and disconnect the antenna.   If this is done the cables need to be clearly labelled so that you plug the handheld into the antenna and not the nav/com, or have the antenna cable loose and the nav/com cable bulkheaded on the bracket.   Or something like that.   Don't try this at home, YMMV, etc., etc.

 

 

 

Edited March 17, 2018 by EricJ

[Marauder]

Do you still have that?   I'd love to pop it open and see if they used the pin jack insertion to isolate the ports.
Meanwhile, I took a couple cable splitters and put them on my lab bench with a couple of Spectrum Analyzers and a Signal Generator.   I connected the signal generator to one of the split ports to simulate transmitting with a handheld, and measured the power output at the input port (which, presumably, would go to the antenna), and the other output port, (which, presumably, would be connected to the in-panel comm receiver).   The antenna output is ~3dB down from the handheld transmitter, and the in-panel comm port is 20dB down from the handheld transmitter. 
There are things other than typical rf splitters that can be used, but I suspect that's usually what gets plugged in.   If something other than a typical splitter is used, results may vary.
However, assuming a typical splitter is used, connected as above, with a handheld with a 7W output the nav/com would see 70mW (~+18.4dBm) at it's receiver input, which isn't too bad.   That's not out of the realm of expectations for a receiver to be able to handle, especially when it is designed for a reasonably harsh environment that deals with lightning and another transmit antenna a few feet away, etc.
Of course the bad news is that the 3dB+ loss to the antenna port means your 7W handheld is instantly turned into a 3.5W handheld, but for VHF AM LOS voice radio 3dB is really not that much, and the advantage of getting to the outside antenna rather than using the handheld antenna inside the airplane is likely greater than that.
A better method might be to have a junction or a union in the coax that could be easily reached so that you can disconnect the antenna cable from the nav/com and connect it directly to the handheld.   That would give you the full 7W to the external antenna.   3dB isn't that much in this application, but it's 3dB you wouldn't have otherwise and if you're on the fringe of reception it'll be noticeable.   This would also avoid the 3dB loss to the in-panel nav/com with a transformer/splitter in place.
My airplane goes into the shop for an avionics-ectomy next month, and I'm thinking of having them delete the KX99 (whatever it does) and just put a bracket there with a connector that I can reach and disconnect the antenna.   If this is done the cables need to be clearly labelled so that you plug the handheld into the antenna and not the nav/com, or have the antenna cable loose and the nav/com cable bulkheaded on the bracket.   Or something like that.   Don't try this at home, YMMV, etc., etc.
 
 
 

Nope. It went into the electronics graveyard with the rest of the misfit and dead toys. I do know that were using some sort of signal strength gizmo to look for loss along the antenna path. They tracked it down to the splitter and it was removed.

The signal loss was also noticeable with the splitter removed but to a lesser extent. I ran all new RG-400 and let the shop makeup the new BNC connectors. This was the stuff I was finding when I pulled the RG-58.




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