2M or Airband?

[cra3y]

both (vx-6r and vx-7r) with mod are able to transmit (TX) on airband (in AM mode). with my vx-6r i have to set TX freq. to 5kHz more that RX one (if RX is 122.700, then I set TX 122,705 for clear and loud transmit).

also i bought dual-band antenna, especially for 122MHz and PMR usage (PMR for everyday use and pilot talk, 122 for comm to my local airport, when I will enter to CTR)

--

best regards

Chris

Edited November 3, 2022 by cra3y

[Phil_P]

I think you'll find that they are transmitting on FM regardless of what the display shows. The display switches to AM as you go onto airband, but the sets I've experienced only receive on AM and transmit on FM even when they have had the band modification.

By tweeking the frequency off slightly, you are relying on slope detection (a crude way of listening to FM transmissions on an AM receiver).

[slim]

both (vx-6r and vx-7r) with mod are able to transmit (TX) on airband (in AM mode). with my vx-6r i have to set TX freq. to 5kHz more that RX one (if RX is 122.700, then I set TX 122,705 for clear and loud transmit).

also i bought dual-band antenna, especially for 122MHz and PMR usage (PMR for everyday use and pilot talk, 122 for comm to my local airport, when I will enter to CTR)

--

best regarda

K.Gajda(cra3y)

Aaaaaaaggghh.

What you are doing is causing interference over a wide range of frequencies. Your radio isn't transmitting AM it is transmitting FM and all you are doing by offsetting your TX frequency is transmitting on an adjacent frequency such that the interference on the main frequency sounds a bit like AM. It appears to work but it won't work all the time and you are in danger of causing interference on other channels.

The CAA and OFCOM have very strict rules about what transmitters can be used on airband for one very simple reason - if you get it wrong people will die. The VX-6R & 7R are not approved for use on airband and are not designed for it either.

If you are going to break the rules please make sure you understand exactly what you are doing and what the impact of your actions are on other people. For an example search for a post of mine containing the phrase "black ski masks"

Yes I am sounding a bit like the radio police and I make no apologies for it - I may not be able to fly particularly well but this is an area where I can claim guru status both on the technical aspects and the legal ramifications.

[pete_b]

both (vx-6r and vx-7r) with mod are able to transmit (TX) on airband (in AM mode). with my vx-6r i have to set TX freq. to 5kHz more that RX one (if RX is 122.700, then I set TX 122,705 for clear and loud transmit).

also i bought dual-band antenna, especially for 122MHz and PMR usage (PMR for everyday use and pilot talk, 122 for comm to my local airport, when I will enter to CTR)

--

best regarda

K.Gajda(cra3y)

Aaaaaaaggghh.

What you are doing is causing interference over a wide range of frequencies. Your radio isn't transmitting AM it is transmitting FM and all you are doing by offsetting your TX frequency is transmitting on an adjacent frequency such that the interference on the main frequency sounds a bit like AM. It appears to work but it won't work all the time and you are in danger of causing interference on other channels.

The CAA and OFCOM have very strict rules about what transmitters can be used on airband for one very simple reason - if you get it wrong people will die. The VX-6R & 7R are not approved for use on airband and are not designed for it either.

If you are going to break the rules please make sure you understand exactly what you are doing and what the impact of your actions are on other people. For an example search for a post of mine containing the phrase "black ski masks"

Yes I am sounding a bit like the radio police and I make no apologies for it - I may not be able to fly particularly well but this is an area where I can claim guru status both on the technical aspects and the legal ramifications.

Listen to him he KNOWS what he is talking about belive me.

Pete b

[gordon_dunn]

Slim,

Is the Icom A6 approved then? Technically it is a true Airband transmitter/reciever, but someone told me it has not been approved by the CAA?

[slim]

You ask a tricky question! The A6 is approved by the FAA (US equivalent of the CAA) for use in the air. The CAA have different rules. If you want to use a radio off the ground then not just the radio but the whole installation has to be approved and registered to the callsign of the aircraft it is installed in. Because of this it is impossible for a handheld radio to be approved by the CAA because it isn't built in to the aircraft.

Having said that the A6 is approved for use on the ground on Airband (obviously it doesn't than have to be installed in an aircraft )

I've had long conversations with the CAA on the subject and unofficially, someone using an airband radio properly (i.e. not causing interference on other frequencies and not ordering pizza on a Heathrow final approach frequency) isn't going to get into any trouble.

I know it isn't a definitive answer but it is the best we have at the moment.

Stuart

[gordon_dunn]

Interesting Slim,

Indeed this is a very sensible approach... most of the guys i know that carry airband do so purely for safety reasons, i don't think anyone would argue that is a bad idea- even though it is technically illegal.

Just to clarify on the legality- if we are using the system sensibly on the correct frequencies, etc... are the CAA the only 'body' that have jurisdiction on this matter?

GD

[cra3y]

What you are doing is causing interference over a wide range of frequencies. Your radio isn't transmitting AM it is transmitting FM and all you are doing by offsetting your TX frequency is transmitting on an adjacent frequency such that the interference on the main frequency sounds a bit like AM. It appears to work but it won't work all the time and you are in danger of causing interference on other channels.

You are wrong, because both radios has FM/AM switch mode - when i switch to FM, the tower "see" busy channel without any sound (only carrier locked the channel). when i switch to AM, everything is ok. for example Vx-5r doesn't have AM transmitter.

my radio was tested with wise persons who's working as radio operator in tower (in local airport) and we tested it with broadband spectrum analyzer (wavetek) and it didn't cause any disturbance over whole freq range.

but You know better?

PS: i doesn't want to encourage any person to mod his ham radio. i modified my vx-6r by with help by qualified personel (in term in radio/tech and operator radio operator to check if everything is ok)

PS2: we used radio before take off and in final approaching - the purpose is to make tower know about our presence, not for bla bla talking about pizza

PS3: in my country there is proposal in new bill to legalize some devices for PPG and PPGG to legalize way to use such (modded and tested by specialized personel) devices to comm with tower - now is like You described - if we doesn't make mess in airband, there will be ok, because knowledge about flying objects (reported by radio) is most important than rest aspects of using radio in airband.

[alan_k]

Interesting Cra3y, are you saying you have had your radio modified to give AM transmit on the VHF band? If so that is a complex modification as it needs changes to the RF stages of the circuit as well as modification to the modulator stages. It is not just a reprogramming exercise.

The specification of the VX radio says it is AM ONLY on the 50MHz (6 m) band.

Alan

[cra3y]

The specification of the VX radio says it is AM ONLY on the 50MHz (6 m) band.

because is locked via firmware/processor. it is like cars engines, the same engine - different output power, because of processor

this is positive aspect of cutting costs. manufacturer doing near the same radios and locking features based on purpose of radio.

yes, vx-6r and vx-7r has AM tranmitter and it could be used with mod and propelly tuned antenna (i have customized duobander tuned on 122 and 434 MHz)

PS: i didn't want to fight with law/caa authorities in this forum. we (i and my ppg friend) have an agreement with local airport to permit to use airband for purpose which I described in previous post. of course i'm not able to use legally airband in different places without such agreement, but i mentioned that there is a bill i my country that should solve PPG and PPGG demanding to communitation with tower.

Edited December 14, 2008 by Guest

[alan_k]

Cra3y, I am not concerned about the legal issue of using this radio, but I am not convinced that it is actually putting out AM.

You mention the cost aspect for the manufacturers, if a multi band radio is designed to be AM on all its bands it is going to be more expensive. The manufacturers are not going to build in features that there isn't a call for.

I can see a demand for AM on the 50MHz band as this is just an amateur radio (Ham)band, but I cannot see a demand for AM on the VHF Ham band or the UHF Ham band.

The radio does not have an 'AM transmitter' that would cover any band that is included in the design. The output stages for 6m, 2m and UHF are all separate circuits and are very unlikely to all be constructed for AM transmit. This requires amplification that is very linear, this is more complex, more expensive and less efficient.

I can't see this in a triple band 100 odd quid radio.

If the radio is AM on all bands then why don't the manufacturers say so in the specification?

Alan

[cra3y]

If the radio is AM on all bands then why don't the manufacturers say so in the specification?

1) because release AM TX capable radio (especially in airband) needed additional certification process? (and having this radio, with TX AM enabled on airband will require special license, which is not needed for radios, whos haven't enabled AM TX in airband - they behave like radio scanner in this band, not radio transmitter)

2) because "John Smith" should buy two complementary radios (one for airband, second for PMR/LPD) and he have to pay twice? (radio producer will do double deal with single person)

3) if something is for everything, there is for nothing? (because is not specialized, so is not fine tuned for specified usage?)

during measure my vx-6r with TX AM on 110-130 MHz, the radio trasnmit best in 125-130 Mhz, 115-125 is acceptable, but 110-115 give poor quality + very loaded TX circuit (voltage drops rappidly and load amperage is very high).

i don't want to say, that both yeasu are developed to support this trasmition, but instead they are capable to transmit in airband with acceptable quality for PPG purpose (slow speed aircraft, like PPG, did't required verly long TX range, my yeasu support about 1km at ground level to about 8-10km in air)

PS: i'm still looking for good ham radio, that will work very well "from the box"(without mod) in airband and PMR/LPD freq.

[slim]

Hi Cra3y.

I didn't say that your radio was causing interference all across the band. I only said it was causing interference on a range of channels (ok I may have used the word "wide" in there as well ). The proof is in what you said about de-tuning your transmit frequency so that the tower can hear you. Your signal will not only be audible on the tower frequency but also the one above. If your radio was transmitting AM then you'd be using the same frequency - he can hear you because of something called slope detection (see AlanK's earlier post in this thread) so you must be transmitting AM.

Airband channels are on frequencies separated by 8.33KHz. If your tower is on 122.700MHz then the next channel up is 122.70833. Your radio cannot do 8.33KHz steps so you've changed the frequency by 5KHz. This means that you are 5KHz off your tower's frequency but only 3.33KHz off the next channel. This means that you are causing interference to someone and as we've already discussed in another thread, radio waves travel a long way when you are in the air.

Amateur Radio 2m frequencies are separated by 12.5KHz, partly because FM uses more spectrum (a wider range of frequencies) than AM. Anyone who really can't sleep is welcome to read the excellent but technical page on Wikipedia http://en.wikipedia.org/wiki/Frequency_modulation. I'm not talking opinion here, I can walk you through the physics. The maths don't lie.

Yes, Kenwood, Yeasu and the other manufacturers do build very similar radios and then turn on or off features in software for different markets but AM transmit on 2m is simply not possible on the VX series handhelds. As AlanK said earlier today, they have a different transmit circuit for 6m, 2m and 70cm. The 2m circuit doesn't have the physical components to do AM.

And finally (yes I do mean finally, if you've read this far and still haven't lost the will to live then you must be at least a little tempted to get an Amateur Radio license ) we have the problem of antenna mismatch and filters. Cra3y mentioned that as the frequency changed the strength of his transmitted signal seemed to drop off, as did the quality. At the frequency that it was designed for, an antenna launches almost all of the electrical energy that the transmitter is generating off into the ether. As you tune away from that frequency less and less of the energy leaves the antenna and more and more of it bounces back into the radio - the first thing it hits is the power transistor that is your final stage amplifier. This wonderful piece of silicon was meant to generate radio waves not absorb them. It copes by getting hot and transmitting on other frequencies to try and get rid of the energy (causing even more interference) - for a little while. Then it melts. Once the smoke escapes it will stop working. PhilB has seen this first hand.

Amateur Radio transceivers are designed for 144MHz to 146MHz where the wavelength is 2.08m to 2.05m. At 122.7MHz the wavelength is 2.44m, almost 25% longer. It is highly likely that more than 50% of the transmitted power is being reflected back into the radio. It could be as much as 90%.

On that note I am going to lay down my geek credentials and go out and have some fun for the evening.

Stuart.

P.S. Gordon - unfortunately the CAA are not the final arbiter of things radio in the UK. OFCOM are. The good news is that they're far too busy to be looking for people breaking the rules. They only get involved if someone complains. The simple solution is to use proper kit and use it properly. You won't cause anyone else a problem, they won't complain and OFCOM won't find out.

[Phil_P]

The earlier comment about handheld radios not being licensable for use in aircraft is inaccurate, as previous models of ICOM handheld have the appropriate type approval (A4 & A22 perhaps). I have spoken at length to the ICOM UK MD who told me that the current CAA type approval requirements are so onerous, that ICOM do not feel it is worthwhile seeking this approval unless the requirements change, the market being so small, the potential return financially is not worth it. The A6 & A24 exceed the specification of the earlier models, but as the goalposts have moved, they don't meet the new regs.

I believe that a handheld can be granted type approval as a removable installation, and does not need to be tied to any particular aircraft callsign. This is my understanding having read the application document for installation approval.

All that said, I doubt that a non-type approved radio will illicit a prosecution providing that it is operated in the appropriate manner and preferably by someone with a Flight RT License. I personally will be continuing to use the IC A24.

[cra3y]

I didn't say that your radio was causing interference all across the band. I only said it was causing interference on a range of channels (ok I may have used the word "wide" in there as well ). The proof is in what you said about de-tuning your transmit frequency so that the tower can hear you. Your signal will not only be audible on the tower frequency but also the one above. If your radio was transmitting AM then you'd be using the same frequency - he can hear you because of something called slope detection (see AlanK's earlier post in this thread) so you must be transmitting AM.

ok, I will ask a person, who's modded my yaesu, what he did (he mentioned, that he also did something else that simply remove solder-jumper connection).

THX for info!

[slim]

Phil,

I'd thought that the installation had to be approved even if the radio could be removed. I'm more than happy to be wrong though. Can you point me in the direction of a web version of the document?

Your point about the Flight RT license is very valid. There is no substitute for proper training in any field (pun intended)

Stuart

[Phil_P]

If you have a look here;

http://www.ofcom.org.uk/static/archive/ ... ical.htm#d

Under 'Aircraft Radio' you will find a reference to the fee for a radio license for a removable installation

Also here;

http://www.caa.co.uk/default.aspx?catid ... =9&faqid=1

The CAA site also has links for checking what equipment meets type approval.

It would seem redundant to have an 'installation certificate' as such for a hand portable radio, however the equipment must be on the CAA approved list.

[flyingdoc]

Hi Guys,

Is the ICOM IC-A6 a usable airband handheld transceiver in the UK?

Seems cheap enough at £180 why do we want 2m?

just my 2p

Snowman

[t_andrews]

Nice thread guys.

I always knew my vx5 was outside it's efficient broadcast spectrum, but chewing through this thread helps me understand why a bit more.

Is the tool I used to open TX up outside factory settings.

It allows step adjustment too, and from what I'm gathering here, I can adjust it to clean up broadcast overlap?