backup Handheld radio antenna

[Cozy1200]

Just pondering some future plans.

 

I plan on putting a com antenna in each winglet and having two radios in the panel.

 

I'd also like to have the ability to hook up a handheld radio in case say electrical failure. I envision a BNC connector somewhere on or under the panel that could be hook up easily in flight.

 

What are the suggestions from the gurus?

 

can I 'Y' off one of the antennas? Put a third antenna in somewhere? Forget the external antenna all together, use the whip antenna on the handheld?

 

I'm still at least a year off, but just thinking about it tonight. (thinking of building, not actually building because I'm sitting in a hotel in the middle of nowhere Australia)

[longez360]

Drew, I have a panel Comm and an Icom that I take on cross countries. I have two winglet antennas. The second antenna RG-400 coax is up in the left leg well which I can connect if I don't get range. I had planned to add a B&C recpeptacle and carry an extension.

[JTest]

G'day Drew

 

I would recommend putting a splitter in line with both antennas. and running them to a BNC plug (or two).

 

I have used the whip antenna that comes with an icom handheld for years, but I also have a BNC plug on my panel of my C172 that gives me connection to the external antenna.

 

I find the range is better with the external antenna and in Oz you just may want the extra range.

 

Try the splitter solution is my suggestion and then you can use the handheld to troubleshoot the radios and antennas...

 

Hope this helps.

 

Jeff

[JCPJCP]

Either a Splitter or a Tee fitting are both the wrong answer.

 

Neither provide isolation between the high RF Power output of the transmitter and the delicate receiver input amplifier.

 

End result may (will) be a dead receiver when you transmit on the second radio.

 

JCP

[daveb]

The idea of a spare is that it is independent of things that might go wrong in the plane. So perhaps it should be separate from all the installed systems? I take an ICOM A23 & pack it with the rubber duckie antenna separate, it fits nicely in a side pocket.

 

I have used in when the installed radio failed and had good coverage after realizing I had to hold it up with my left hand to get the antenna clear of the surrounding metal bits.

 

The other extra is a fitting that goes from headset to the radio for the speakers and mike. Using the handheld radio's PTT is easy and allows another redundancy.

 

An extra might be to consider a fused output for radio power to backup the battery and maybe things that passengers might want to use? CD player/computer/toaster...

[JTest]

G'day

 

Here is the web site for just one Duplexer (splitter) that is available on the market.

 

http://www.comant.com/productdetail.aspx?PID=210

 

The CI601

Dual communication/single antenna duplexer designed to provide operation between two transceivers and one antenna. In the de-energize mode, the diplexer acts as a 3 dB coupler with the output ports isolated by 20dB. Control voltage actuated by the microphone circuit switches the antenna to transmitter No. 1 or transmitter No. 2.

 

Yes, you can connect two transceivers to one antenna. I recommend if you wish to have a panel mount BNC connection for the handheld you may just wish to run an extra copper dipole antenna on the fuselage (unless the plane is completed already.

 

I hope this helps.

 

Jeff

[JCPJCP]

This device acts as a passive splitter on receive, which is OK.

 

But on transmit it acts as a relay, which solves the isolation problem.

 

Unique gadget.

 

JCP

[Lynn Erickson]

This device acts as a passive splitter on receive, which is OK.

 

But on transmit it acts as a relay, which solves the isolation problem.

 

Unique gadget.

 

JCP

it will also isolate you from your money, only costs $900 so i think adding an antenna might be a little cheaper way to go

[JTest]

it will also isolate you from your money, only costs $900 so i think adding an antenna might be a little cheaper way to go

G'day

 

Do some shopping, I have found it on-line new for under $500. I agree it is expensive for a couple of zener diodes.

 

The zener diode can be used as a switch by using the bias of the diode as a switch. They will block transmission (high power) from the other radio, but will let transmissions out and also let low power (reception) pass.

 

Jeff

[emteeoh]

Its been a while since I played with them, but as I recall, you could isolate the two radios using a simple circuit called a hybrid. They used to use them to build telephones. It is, as I recall, 3 coils of wire around an iron core (ie: a transformer, more or less). In the telephone, its set up so that signals from the line go to the speaker but not the microphone, and signals from the microphone go to the line, with a weaker signal going to the speaker ( so that you have some feedback as to how loud you need to speak). Anyhow, as long as you can find some info about its design, it should be a simple part to obtain, or at worst, hand-wind.

 

http://en.wikipedia.org/wiki/Hybrid_coil

[JTest]

Its been a while since I played with them, but as I recall, you could isolate the two radios using a simple circuit called a hybrid. They used to use them to build telephones. It is, as I recall, 3 coils of wire around an iron core (ie: a transformer, more or less). In the telephone, its set up so that signals from the line go to the speaker but not the microphone, and signals from the microphone go to the line, with a weaker signal going to the speaker ( so that you have some feedback as to how loud you need to speak). Anyhow, as long as you can find some info about its design, it should be a simple part to obtain, or at worst, hand-wind.

 

http://en.wikipedia.org/wiki/Hybrid_coil

G'day

 

Yeah, you can find several schematics on some of the Ham operators pages. I would use a couple of old marine radios to test. They are cheaper and if you blow them up you only lost about $10 to $20 per unit if you get them on eBay.

 

It should all fit into a Arnetts can. You may even want to build them for $300 and go into business.... Hmmm, no I already have to much on the workbench. Maybe in a year or so....

 

Good luck and keep us posted.

 

Jeff

[JCPJCP]

RF 101 lesson:

 

1) PIN diodes are used as RF Switches, Zener Diodes are used as voltage regulators.

 

2) What an RF Engineer calls a "Splitter" is actually a "hybrid". There are many ways to build one, but the telephone hybrid is a good example.

 

3) All Hybrids have 4 ports, in our case the antenna, 2 radios, and a dummy load.

 

4) On transmit, half the power would go to the antenna, and half to the dummy load. The dummy load has to be capable of absorbing 1/2th the transmit power without burning up. (not a typical cable tv splitter !)

 

5) And the receive signal also splits equally between the two radios.

 

6) Isolation from one radio to the other typically runs 20 dB, hence 1/100th of the transmit power would be presented to the opposite radio input.

 

BUT (there is always a BUT !)

 

7) This all depends upon a perfect match to the antenna.

 

8) Power reflected by a mismatch to the antenna again split between the two radios, just as a receive signal does.

 

Hence

 

9) With a typical antenna, power presented to opposite radio can quickly approach or exceed 10% of the transmitters power.

 

10) This is why the $900 box contains a switching circuit on transmit.

 

Hope this clears up some misconceptions.

 

JCP (I'm an RF Engineer for the last 38 years !)

[JTest]

G'day JCP

 

The Zener diode is the switch. I used them in variable antennas on the Guardrail \ Quicklook \ Common Sensor airborne platform. By applying forward or reverse bios the zener will block or pass signals. The a/c used six different radios to listen and three to communicate on several bands. I do not question your experience.

 

I only said that it can be done, and the price is around $400 for the CI601 if you shop it. I think it may be possible to get one second hand for less.

 

 

Thank you for the RF 101 lesson. Do you think a 50 ohm terminal load from Radio Shack would work as a dummy load?

 

Jeff

[Lifessamsara]

Hi Gang,

 

I know it is not quite as elegant a solution as the discussion so far, but what about a manual panel selection of RF? With some additional thinking the audio of both the panel mount rx/tx and the back-up hand held could be coupled while still leaving the hand held unit able to to removed from the aircraft simply and easily.

Have a look down this path and see what the collective (borg?) think

 

http://www.pasternack.com/product-MANUAL-COAX-SWITCH-WITH-SURGE-PROTECTOR-2-OUTPUT-PORTS-PE7139-71926.html

 

Just my 2 bobs worth.....

 

Bruce.

[JCPJCP]

Radio Shack stuff can be very suspect at times. At they sold an UHF right angle connector that used a spring (think of a ball point pen spring) to "turn the corner" of the center conductor. While it worked OK on Citizens Band (27 MHz), was totally worthless at VHF and UHF.

 

Yes, a fairly good coaxial switch will work, but opens chance of being in the wrong position.

 

For a back up, an additional antenna, perhaps up the side of the cockpit behind the front seat, it the simplest and best solution.

 

Just separate it from you comm antenna's (winglets) and localizer antenna (canard).

 

I give up on Zener vs PIN, not worth arguing about.

 

JCP

[Cozy1200]

Thanks all. I'm not sure what direction I'll go, but it gives me something to ponder.

 

The splitter (hybrid) is interesting, but I really don't anticipate needing to use the hand-held if the others are working. So why spend a lot of $$ if it's not being used at the same time. Question: does the hybrid reduce the range or effectiveness of the antenna?

 

The third antenna is a possibility, but I don't see a really good place to put it yet. I do like the simplicity of this idea plus is a completely independent system. Another antenna would be cheap if done during construction.

 

A switch on the panel is something I didn't consider. As long the the antenna and switch are good, it should be isolated from the radios.

[argoldman]

Thanks all. I'm not sure what direction I'll go, but it gives me something to ponder.

 

The splitter (hybrid) is interesting, but I really don't anticipate needing to use the hand-held if the others are working. So why spend a lot of $$ if it's not being used at the same time. Question: does the hybrid reduce the range or effectiveness of the antenna?

 

The third antenna is a possibility, but I don't see a really good place to put it yet. I do like the simplicity of this idea plus is a completely independent system. Another antenna would be cheap if done during construction.

 

A switch on the panel is something I didn't consider. As long the the antenna and switch are good, it should be isolated from the radios.

 

If you want to do it on the cheap, bring one of your com antennas to a male BNC (chassis mount) mounted on your panel. Then bring your antenna wire from your tranciever to a close position on your panel with a loop of wire (doesn't have to be long) with a female BNC on the end of it. Connect the two together for normal operation. Make a jumper cable from our handheld with a female BNC on the free end (make the cable long enough so you don't have to stretch when connected to the above mentioned bnc on the panel. The if you want to use your handheld, disconnect the female from the assembly and connect the female from your handheld.

 

No switch cost very little.

 

She may be ugly, but she sure can cook:cool:

[jprock]

I would also make sure that any open BNC connectors have a terminator at the end. These will eliminate any RF noise that an open BNC connector can pick up. Cheap insurance...

 

http://www.cablesnmor.com/bnc-terminator-75ohm.aspx

[argoldman]

I would also make sure that any open BNC connectors have a terminator at the end. These will eliminate any RF noise that an open BNC connector can pick up. Cheap insurance...

 

http://www.cablesnmor.com/bnc-terminator-75ohm.aspx

 

Great Idea JP

 

Make sure they are the right impedance-- those listed on the site are 75 ohm, don't we operate with 50 ohm impedance.-- or has my mind slipped another cog?

[dirtdox]

I found this on the Spruce web site. Is this what you had in mind?

 

 

 

http://www.aircraftspruce.com/catalog/avpages/icomswitchbox.php

[argoldman]

I found this on the Spruce web site. Is this what you had in mind?

 

 

 

http://www.aircraftspruce.com/catalog/avpages/icomswitchbox.php

 

Sometimes what we look for is right under our spruce. that's the switch that was talked about. Really simplifies things:)