Update on some RF experience

[ZULU1]

Thought I would share this...

Just when we thought we had conquered the Rf "challenges" with trikes, last week we had a small smack behind the ear !! Hence I wish to share this with the forum..Big boys we are and now only slightly embarassed !!

Our forum member "Massimo" bought a nice pair of helmets from ourselves..all is well, Slow poke gave his radio/chatterbox (Vertex Standard VXA 210) a few hours up and down the coast turning fuel into noise, with our headets and the "new power supply". No problem, all is well on Zulu1 (HKS powered Aquilla). So in all good faith sent the toys off.

Phone call from the customer..terrible whistle in the ears. So we happened to be in Gauteng and hot footed across to Microland. Sure thing same aerie as mine, but Rf as i have said before is a black art. After a few minutes of extreme frustration we headed home, (highly embarassed I may add)..1 O'clock in the morning and a RF bead on the power supply. Problem solved. So it seems that some model Vertex radios create a loop in the power side.

I hope this helps some chaps with installations that give problems, the best bead to acquire incidentally is the unit supplied with the Icom charger as it works a treat !!

Will keep the forum posted on other findings as they arise..

eish Zulu1

[t-bird]

Hi Zulu

I have bought an Ela gyro and also experienced a terrible whistle in the ears on Sunday.
The radio is a filser ATR 500
GPS – 296
Aerial mounted on nose with base plate and body is carbon fiber.
How do I identify the problem ?
Will it help if I move the aerial away from the radio and GPS ?
Will an external gps aerial help ?
Where do I get some RF beads ? Where do I put them ?

[ZULU1]

Hiya t-bird.

May as well place answer on the forum..firstly we need to ascertain the source of noise ??

Is it Rf induced ie from the antenna or other device back in to the headsets cables etc. or is it a audio feedback ??

The Garmin GPS 296 is a real bad animal for introducing noise but not neceesarily whistles. The Filser is really a excellent radio and if I am not mistaken its a 1 watt output which is more than sufficient. This will limit any potential rf ingress in itself.

At this point I may add that this project is without question a Black art, sometimes you get it quickly and sometimes a longer time is required..

Firstly remove the GPS completely and press the PTT does this give a whistle/ whine and so on ?

If so it is required to define the whistle, ie touching antenna, power cables and so on, does this noise change in frequency and or volume. If so then its realted to antenna location and possibly the ground plane. As an example the Quiks and so on have ally tape, this is not ideal and the Aquilla has a front mounted antenna. In a trike environment we use our King Post antenna. As yet we have not mounted one on a Gyro. BUT we can do so and make tooling if required. That nails it immediately..

Next step, Audio ingress..does the Filser have adjustable side tone, turn this back to reduce audio possible ingress. Does it have mic gain, if so turn it back until it stops. The Icom ICA 6/24 is notable for these problems. At this juncture report back..please leave the GPS in the hangar as it confuses details.

If you are having a power feed "feedback" ingress this is identified by touching the power supply in, also the whistle changes accordingly..You need Rf beads and it will nail it..The Vertex Standard VXA210 is notable for this problem.

Rf beads are available from ourselves or alternatively RS Components or Farnells (Mantech in SA). I will post the part nos required from the office in the morning. Or a Icom charger !!

Try this first and dont spend any money until the source is in fact found. I think report back on the forum for us all to learn this frustrating problem.

I will endeavour to nail it with my experience.

Oh... What headsets do you have and is the intercom the Filser inbuilt unit ?? Do you have digital instruments, does it happen on any specific frequency and anything else you can advise.

qedila Zulu1

[t-bird]

Thanks Zulu

I will try it over the weekend.
The filser radio have a built-in intercom.
The headsets is lightspeed qfr solo with an adjustable gain on the mike.
No other digital instruments.

[t-bird]

Hi Zulu

After taking everything apart, I still had the interference on the GPS and Radio.
I then bought an antenna from Butch at Bennies hardware.
The antenna consist of two straight pieces a long one at the top and a sorter one at the bottom.
The shorter one is probably the same as a base plate.
I have mounted the antenna on the Rotor boom. The radio is now working perfectly and I have no interference from the GPS.
I went for a test flight to Ellisras works like a charm received transmissions from Carltonville and Nylstroom

[ZULU1]

Hiya T Bird

The SWR may not be correct but if it works thats brilliant, as I suspected it has to be moved away from the GPS.

Well done

Paul

[Perry]

Folks,

Invest in one of Zulu1's Vee Rabbits - they are the best antenna we have used - we have chucked (yes binned) all our others since getting this gear.

I am sure Paul could get it to fit on the mast for you as well.

Regards

Perry

[Aerosan]

something interesting from me as well, Im not sure if this has always been there but this weekend I saw, purely by chance, that whenever I transmit my egt and rpm gauges double or tripple!!!! and only for the time you transmit. Not sure what the hassle is and Im in no way implying any problem from Mr Zulu. There is absolutely NO connection between the instruments,(skydat) exept for the powersupply of course and then my radio is supplied from a Zulu filter unit.

I will still investigate and give Mr Zulu a call.
San

[John Young]

...whenever I transmit my egt and rpm gauges double or tripple!!!!

Hi San,

Try this one ....

viewtopic.php?t=5066

Regards
John ZU-CIB

[Bennie Vorster]

...whenever I transmit my egt and rpm gauges double or tripple!!!!

Hi San,

Try this one ....

viewtopic.php?t=5066

Regards
John ZU-CIB

Or turn the voluim down.

Zulu what is the max leagle output for an aviation radio and what is the max output it can be set to?

[ZULU1]

Hi Benny

I am unsure on legal outputs of radios, however as a retro fit project we are doing for a Central African air force i can advise the following tests.

I have installed/tested the ICOM ICA 200 (type certified ) which delivers (correct wording) a full 12 watts. I hitched the worms and other kit in the pannier of ZU-LUI with a seperate supply from the battery, cranked the mic gain up to maximum that I could get away with, connected to a Vee Rabbit and then went flying. I flattened every frequency and everybody within about 10ks, rattled Dave Jacksons cage. It was so vicious it even bled over to other frequencies (spurious). So in short not a good idea to consider that set up. It distorted speech within 5kms !!

As part of the same project I took a ICA 6 and turned the power down to a half watt, the mic gain also cranked up to maximum with the Vee rabbit and contacted Margate tower and Richards Bay. The transmissions were clear distortion free and perfect using the same headsets. I still use that radio on half watt by the way..

The Microairs come in with a five watt output, they are attached to normally a small 1/4 wave whip without a good ground plane. Now dont wish to go into VSWR etc. but if the ground plane is poor then your antenna will send that rf it cant get rid of all over the place, instruments whistles, local township TV..you name its gotta go somewhere. I have turned several down with good results..the small sticker on the left hand side is a small screw, turn it back.

So Bennie in my experience, 1,5 watts is perfect, but far more importantly a good antenna will do you much more good than any amount of power that you wish to pump out, it cleans the entire show up. Secondly and equally important is a good power supply. Now here if you have space, first prize is a second battery and for short flights just use the radios. The new Vertex radios are Li Ion (and some Icoms) they last for ever. My policy is KISS (Keep it simple stupid). At the end of the day you just need comfortable simple comms that work.

Whilst on the subject of line filters, I may add some further tests as we are doing some big Mil toys at present. The benefits of this forum are that we are all learning, I always listen to others comments.

Anyway I took some torroids and with my colleagues we went looking for a back to back test, over 20k they are awesome, but a wire choke below 10k will out perform line noise. However the torroid is better for rf suppression through the range. Each device has to be selected for specific frequencies. So we stay with our initial experience and use a combination of wire line chokes and rf beads (must get correct frequency). The best rf beads come with Icom mains chargers !! I use a Jonway scooter with all suppression devices removed for power and line tests, it blows headlight bulbs and sometimes peaks at 60 volts but does the job for me !!

i attach a pic of our military intercom board clearly showing a wire line choke, rf beads at specific points with a LM7805 and LM386
.
This really works well as it removes rf at specific points, mic amps etc. the unit illustrated is on a bus and can accept a high number of headsets and will accept three radios in.

eish zulu1

[Aerosan]

Thanx John I will do just that. Im just surprised that I never saw this before!! Im also not sure how this can happen, looking at my installation that is

Zulu what is your bit on this? I have the nice Zulu PSU on the same 12v line that supplies the instruments and then the psu supplies the radio.

San

[ZULU1]

Hiya Aerosan

I am unsure at this stage where the problem comes from not seeing the installation, I know that the ICA 5 is a true 1,5 watts. In the past when we install Vee rabbits then it stops rf getting into instruments. BUT, If you look at the thread that started all this; Massimos, his gauges also went hectic as well until we placed the rf bead on the power supply to the radio.

So why not try a rf bead, use the one supplied by Icom with the charger on the power lead to the radio ??

As I have said before this is Black art and I learn daily so its a good project to learn on..then maybe try removing power supply from plane..

eish Zulu1

[Rudix]

I find that in many cases where you get RF feedback into other equipment it is caused by a high SWR. I often run hundreds of watts of RF power (At home and in the car) without problems if the antenna is nicely matched and resonant but you can have problems even with 500mw if the SWR is high. The reflected RF has to go somewhere !

I have measured the SWR on a few plane installations and they were horrible ! Remember the environment (plane construction, shape and antenna position) all affects SWR so you cannot always take a "perfect" antenna, install it and expect the SWR to still be low, for best results the SRW must be checked and adjusted once the antenna is installed.

For best results use an antenna analyzer and not just a SWR meter, it will show you where the antenna resonates (If it does !) and the actual impedance. A SWR meter can be fooled, remember a perfect dummy load will have a nice low SWR on a SWR meter :D

Regards,
Rudi

[ZULU1]

Thats correct, you can even use the cable length between the transmission device and the antenna to "fool" the SWR. I am not a ham but it can be done.

Maybe you can inform us on the formula ??

eish Zulu1