Radios

[extralite]

Had a good weekend getting the latest Thruster together and airborne. Quite nose heavy so a weight and balance check next. That's 5. Ready for a get together soon. 

 

Has anyone managed to get good VHF coms in their thruster and if so how? The VHF aerials for 2 are placed back behind the cockpit, on the centre boom, but still very staticy. One is an ICOM in dash, the other hand hand with remote aerial. They receieve well, lot of noise on transmit. Any tips appreciated. 

[cherk]

MobileOne.com.au

 https://www.mobileone.com.au/images_antennas_airband/airkit.png

Edited November 8, 2022 by cherk

[Blueadventures]

Have you got a capacitor fitted to clean up voltage spikes?

[RFguy]

some of the rotax have an RPM indicator coupled to one of the spark plug leads, and they will generate an antenna for the static source.

 

where is the RPM tacho source from with your rotax ? that wire may be radiating. 

I would recommend the antenna under and behind you. or up near the tail.  IE away from the engine...

[FlyBoy1960]

2 hours ago, cherk said:

MobileOne.com.au

 https://www.mobileone.com.au/images_antennas_airband/airkit.png

Sorry but these aerials are really TERRIBLE.  I have the RF plots somewhere.

 

[FlyBoy1960]

Found them, the range is just so NARROW it will cook most radios at either end of the frequency range.

 

 

Mobile 1 Ground plane independent VHF aerial system

[RFguy]

They are quite narrow. but they are typical of most efficient air band antennas

you cant have efficiency and wide bandwidth

 

many antennas (like the swept back ones  use lossy resistors or lossy elements  in them to improve bandwidth (throw away half the power and signal) 

there is no free lunch in this game

MOST of the swept back airband antennas have awful VSWR, and or a resistor  to even them out.

You'll find it very hard to find a published curve for them- they dont want you to know how bad they are! 

Mobile One have been honest.

 

Suggestions : 

 

BTW no antennas are truly ground independent, just ground less dependent.

The mobile one ground independent is very narrow. If you have metal in your frame there is no point to using a ground independent, you'll suffer narrow band.

 

just go a mobileone quarterwave whip. not the mobileone ground independent

on the mobileone site- the  M124-1 whip. 

https://mobileone.com.au/5b_airband.html

 

and you want a UB5BNC base , coax and connector

https://mobileone.com.au/7c_cables.html#ul12bnc

 

 

 

The mobile one antenna that FlyBoy doesnt like - they can be OK with a 3dB attenuator in series- this is 

made from standard RG58 polyethelyne dielectric- not the low loss foam stuff) - you'll need 15m coiled up.

OR you can buy a 3dB attenuator inline coaxial 

 

https://www.ebay.com/itm/373625363386?mkcid=16&mkevt=1&mkrid=711-127632-2357-0&ssspo=Y3gm5yYcQcy&sssrc=2047675&ssuid=&var=642635709538&widget_ver=artemis&media=COPY

 

That will make the antenna OK for the radio over the whole band. 

BUT I suggest the quarter wave whip instead of the ground independent (assumign you have a metal frame.)

if you dont have a metal frame, use the quarter wave which with two wire ground wires 180 deg to eachother, approx 59cm long . make them thick- out of 10mm wide strip of copper tape or ally tape. or just 10-20mm wide 1mm ally strip.

 

you'll need to drill and wire the threaded antenna base. 

 

 

 

 

Edited November 8, 2022 by RFguy

[Thruster88]

2 hours ago, RFguy said:

some of the rotax have an RPM indicator coupled to one of the spark plug leads, and they will generate an antenna for the static source.

 

where is the RPM tacho source from with your rotax ? that wire may be radiating. 

I would recommend the antenna under and behind you. or up near the tail.  IE away from the engine...

The tacho on a Rotax 582 is driven from a single coil in the alternator, there are 8 other coils to generate electricity. A permanent magnet spins around the out side motorcycle style. 

[RFguy]

OK different to a 400 series 2 stoke rotax I think it was I saw ? Maybe that was a Hirth . 

 

[jackc]

Ferrite beads can be your friend 🙂 

[RFguy]

they can... if the source if the interference is conducted on the cable not radiated. 

 

beads on the coax can help stop garbage being coupled onto the outer shield of the cable, (say behind the dash) 

and then the interferene is carried on the outside of the shield of the coax cable al the way to your antenna... where the antenna picks it up from the shield.....

in this case, good to use beads (half  a dozen ) just after the coax leaves the dash.

a few a quarter wave away on the coax from the antenna may assist.

 

however, in fibreglass aircraft, usually gargage is directly pocked up from the antenna

 

[Jabiru7252]

On 08/11/2022 at 2:22 PM, FlyBoy1960 said:

Found them, the range is just so NARROW it will cook most radios at either end of the frequency range.

 

 

Mobile 1 Ground plane independent VHF aerial system

Given the huge price we pay for aviation radios I would say that they would have protection against high SWR. It's easy to implement, being found in cheap CB radios. If my radio was 'cooked' because the antenna was rubbish I would have every right to shove the radio down the manufacturer's throat.

[facthunter]

I find it completely remarkable that after all these years we don't seem to have better aircraft radios. Nev

[jackc]

It’s easy in theory, but millions of radios need to be replaced globally and it would be a mammoth task, already there have been changes in existing radios from 25Khz channel spacing to 8.33Khz which offers more frequencies with narrower bandwidth which helps with noise rejection etc, along with reducing adjacent frequency interference.

 To make a total design change using modern technology is very possible with a different modulation scheme etc etc but imagine rolling that out, globally.  Not to mention costs and certifications etc.

I think we will be stuck with what we have for a long time for our primary radios 🙂