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hash noise on icom handheld.


hihosland
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I have an Icom handheld hardwired into the 912 UL powered Skyranger. Radio works very well however at just under 5000 revs a very pronounced background 'hash' sound abruptly cuts in. Drop the revs back a bit and it stops.

 

Any and all suggestions greatlyfully received.

 

Davidh

 

 

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Guest Michael Coates

Hand-held radios are exactly that "hand-helds" they are not designed to use in aircraft but having said that there are a lot of them out there and they can be successfully adapted. Obviously the noise you are hearing is electrical/ignition noise because it comes in as the revs are increased. The best way to fix your problem is to insulate the radio from the ignition source.

 

You need to give us more information about the installation, are you only running of the battery or are you running off 12 V which are supplied from the aircraft ? Are you using the standard aerial or do you have another aerial attached to the top of the hand-held to an external aerial. Is the system grounded ?

 

There are 100 things that we can suggest but we need to know more about the installation, my guess is without knowing anything else if you replace the coax cable with RG 400 double shielded coax the problem will go away, if you are trying to use the standard rubber ducky on top of the hand-held you are wasting your time. You may also have to filter the power supply running the radio from the aircraft 12 V system.

 

Please give us more information and we can help

 

 

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Michael, you must be a radio retailer. I have heard that old quote about handhelds not being for aircraft use, but the bloke who sells you the Icom handheld will also sell you the headset to go with it and Icom package the cable to connect the headset.

 

If you want a radio for an ultralight, the handheld is what the retailer is going to offer you.

 

Having said that, I used handhelds for years and have just fitted an Icom A200. Wonderful, I now get worse noise than I did with the handheld. Works real well until about 2000rpm on the Jab engine then it sounds like ignition noise, turning off each mag makes no difference. The only problem is that the comms experts are not at the local airport and are extremely busy, so I am still battling on.

 

 

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Guest Michael Coates
Michael, you must be a radio retailer. I have heard that old quote about handhelds not being for aircraft use, but the bloke who sells you the Icom handheld will also sell you the headset to go with it and Icom package the cable to connect the headset..

Yes i am and yes i know... We get about 3 calls a week with people frustrated and who have tried absolutely everything to get a handheld working and they end up spending more than a panel mount radio in the end anyway and it still doesn’t work. It annoys the customer and it annoys me because they have (in many cases) wasted money.

 

 

There is a good resource on our website regarding radio problems and noise etc, Radio instillation is not rocket science BUT you must do the install properly to get a result that works and this includes using the correct materials.

 

 

Most planes are not wired correctly to start with, not because the owner does it wrong but because he doesn’t know any better....

 

 

Try http://www.mcp.com.au/xcom760/faq/wiring-aircraft.pdf as a starting point and wade through XCOM760 VHF Aircraft Radio - FAQ for more info.

 

 

Come back to me with any questions, thanks

 

 

 

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Guest Michael Coates
This post is replacing a post that has been hidden as it is being considered for moderation.

Thank you for putting my reply to Yenn back into the forum after it was removed for moderation.

 

I didn't think there was anything commercial about my reply because I'm not trying to sell anything, I'm simply referring one of your forum members to a valuable repository of information on our website which may help him further diagnose and fix the problems in his aircraft.

 

 

 

 

 

 

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Thanks Michael,

 

for the advice.

 

Question

 

how does one tell if one already has RG 400 double shielded coax other than making the quite reasonable assumption that one does not??

 

Why would the noise suddenly cut in at 5000RPM? rather than slowly build up as the rev increase.

 

What mechanism could be involved in this apparent abrupt threashold?

 

best of wishes

 

Davidh

 

 

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Guest Michael Coates

RG 400 cable is double shielded and it is much more difficult to bend that normal coax cable. It is usually (but not always) a Brown/Tan colour and it will usually have the specification including the word RG 400 on the outside of the cable.

 

The real simple way to check however is to simply cut the cable and have a look at the shielding (although this is not always possible if it is installed in your aircraft) there should be two distinct layers of shielding, hence the name double shielded coax.

 

It is just a coincidence that the noise is cutting in at 5000 rpm, it could be 2000 rpm or it could be 4500 rpm it is just when the threshold increases enough to break in the squelch.

 

You also need to check the grounding of the aircraft because most rag and tube aircraft are not always good aircraft for grounding because of all the corrosion between the aluminium tubes and the bolts etc.

 

Basically in real simple terms you should have one wire (ground wire) coming from the battery un-interrupted all the way to the regulator where if you have a look on the side of the Rotax regulator you will see a grounding symbol. This wire should be around 16 mm² minimum and in one single length. Do not try and cheat and run the grounding through the airframe because you will get resistance as everything starts to corrode. From this one point on the regulator you then run another wire of the same size out to the back of the starter motor as the engine ground and from the same point you run a wire back to your panel which then becomes the avionics ground.

 

Leapfrogging grounds all around your aircraft will create problems as you can see from your experience. If you have a look at the diagram in my reposted reply there is a drawing called "how to wire up and LSA aircraft" and this will give you all of the information you need on how to do it properly.

 

I am actually just fitting a new Rotax engine into a Hanuman X-Air aircraft and it is very interesting going through the latest installation manual regarding grounding, the use of a capacitor, a wire size and the fact that the body of the regulator must be grounded with no resistance and temperature considerations that were not there before. interesting !

 

 

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Thanks Michael.

 

My setup is very similar to your wiring diagram except that the earth runs direct from radio to battery as they are very close together. The other difference is the P leads from the mags are co axial cable both ways from the mag to switch and then to earth on the engine. That was done to reduce the possible effect of ignition pulses even before I fitted a radio.

 

I know Jab engines are supposed to be electrically noisy and am looking for a filter.

 

 

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Guest Michael Coates

You probably need to connect a 22,000 uF Electrolytic Capacitor.

 

Q: I am getting noise or a hiss coming trough the headsets ??

 

A: Probably the hardest of all questions to answer, generally it's interference of some kind, usually electrical but sometimes it can come from the aerial.

 

Each aircraft powered by either the Rotax or Jabiru engines MUST be fitted with an Electrolytic Capacitor rated at 22,000 uF at 25V, this will assist in eliminating most of the problems and to prevent spikes from the aircraft's power supply which can damage the radio.

 

========================================================

 

Q: How do I hook up the electrolytic capacitor ??

 

A: Hopefully this simple diagram will assist you in hooking up the electrolytic capacitor. Please make sure the capacitor is fitted on the power supply side of the fuse as shown in the attached diagram. Try and keep all of the wires as short as possible and position the capacitor close to the radio for best performance. Please note that the capacitor is polarity sensitive, that is there is a positive and negative side to the capacitor.

 

 

 

 

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