8.33hz radios

[The Westmorland Flyer]

Whilst it is perhaps inevitable that 8.33kHz will eventually become the required standard, I think this is going to end up as another Mode-S debacle, with similarly protracted deferrals.

In essence, 8.33kHz is not backwards compatible with 25kHz: where 8.33kHz channels are deployed, 25kHz channel radios can't be used because they will receive more than one channel simultaneously. This makes the imposition of 8.33kHz far more devastating than the Mode-S saga.

HOWEVER...

At the moment 8.33kHz is only implemented in a small part at the top end of the airband spectrum. This area is used by, inter alia, Class-A airspace service providers and for company frequencies. Whilst the split between 8.33kHz spectrum and 25kHz spectrum is bound to change over time, I think it highly probable that there will be 25kHz spectrum for lower level airspace, small regional airfields, etc. well into the future.

Certainly if all other things were equal then this would be the outcome. Unfortunately, another force acts against the retention of 25kHz. Spectrum Pricing encourages airfields to go 8.33kHz as it will reduce their, now considerable, annual licence fees.

The showdown will be interesting.

The doomsday scenario is that spectrum pricing forces small airfields to go non-radio and 8.33kHz forces the lower end of GA to follow suit. CAA (SRG) is aware of this scenario and is rightly concerned from a safety point of view. AOPA is, I understand, on the case. The LAA should also be taking an interest.

The more practical scenario is that 8.33kHz is implemented in stages, leaving the channels that us LAA types use in the 25kHz spectrum for the foreseeable future. The Eurocontrol legislation permits this and it is up to all of us to exert pressure on the CAA to implement the legislation in a common sense fashion, rather than its usual approach to enforce immediately, in full and with gold plating. The Mode-S debacle is a useful precedent.

It makes no sense to fit 25kHz only kit to new builds now, just as it makes no sense to fit anything other than a Mode-S transponder. For those of us that are already flying, it makes little sense, for the time being, to rip out perfectly serviceable radios. My guess is that we'll still be saying the same thing in five years time.

[John Clarke]

I'll wait till the last possible moment before fitting a new radio as there's bound to be a far better choice of radios on the market by then and the cost will, of course, drop dramatically...just like Mode S transponders .

[John Brady]

I don't usually get into this sort of thing but a previous post saying that 8.33 radios are not "backwards compatable" is just nonsense.

After and during the change-over 8.33 channels will live alongside 25 kHz frequencies. For example the FIS frequencies and 121.5 will be 25 kHz and your local airfield and regional radar will be 8.33. Although you could know which is which you don't need to bother because your 8.33 radio will do both and take care of that automatically. Put an 8.33 set in today and it will work just fine on 25 kHz.

Magic? No just clever wiggly amps.

Read all about it the next LAA magazine wot I have just wrote.

John

This is your captain speaking .... there is no cause for alarm

[Donald Walker]

This is your captain speaking .... there is no cause for alarm

[The Westmorland Flyer]

I don't usually get into this sort of thing but a previous post saying that 8.33 radios are not "backwards compatable" is just nonsense.

I'm afraid I do not agree. This issue is not whether 8.33kHz capable radios are backwards compatible. They are - via a cunning technical trick that, by the way, also reduces the number of 8.33kHz channels available by one third. The issue is that the deployment of 8.33kHz is not backwards compatible with existing airborne equipment. When (if) 8.33 is deployed in the frequency ranges used by us, our 25kHz radios will not work.

The reason for this is that 25kHz channel radios have IF filters that are approximately 15kHz wide at the -6dB point. Let's say that the radio is tuned to 123.600MHz (a 25kHz channel). The adjacent 8.33kHz channels are at 123.60833MHz and 123.59167MHz. AM sidebands from these adjacent frequencies spread ±3kHz from the transmit frequencies, and that puts the near sidebands WELL within the ±7.5kHz bandwidth of the 25kHz radio IF filter.

This means that once 8.33kHz is deployed at airfield level, 25kHz radios will be liable to pick up anything up to three separate transmissions (two of them probably rather badly distorted). Now, of course, this can be avoided by carefully allocating channels that are well apart within a given geographical area but that utterly defeats to purpose of 8.33, which is to create more usable channels.

The only solution will be to fit 8.33kHz radios to your aircraft at considerable expense for nil benefit. I therefore stick with my statement that deployment of 8.33kHz is not backward compatible with existing airborne equipment.

No alarm necessary but definitely occasion for a sharp intake of breath at the expensive futility of it all.

[tnowak]

I don't think the issue with 8.33KHz channel spacing is any different to the issue we had many, many, years ago when we had to upgrade our 360 channel radios to 720/760 channel radios.
New specification radios will be needed to receive the new, additional, extra channels.
There will be some interference experienced by 720/760 channel radios if two/three adjacent 8.33 KHz channels transmit simultaneously, and your "old" radio is trying to communicate on a 25 Khz frequency in that channel range.
One would like to think that whoever manages frequency allocation will keep that technical fact in mind (for a while anyway).

Tony Nowak

[The Westmorland Flyer]

You're right in principle Tony but there are some differences that make this change more problematical.

When channel spacings were 100kHz, then 50kHz and eventually 25kHz, the receiver IF filters, which set the effective channel width, remained more or less the same at 15kHz wide. Admittedly in the old radios the shape factor would have been worse because of the limits of technology at the time but in principle the channel width remained the same.

This is as much a characteristic of AM transmission as anything else. A communications-quality double sideband + carrier (AM) signal requires a bandwidth of around 6kHz. In the days before synthesised radios it was not unusual for transmit and receive frequencies to be off by a few kHz - again a limitation of the technology of the day. A 15kHz receiver IF bandwidth of 15kHz gave a fair bit of leeway and was fine right up until the advent of 8.33kHz. With the channel spacing reduced to 8.33kHz, channel width becomes a problem in a way that it never was before.

You're absolutely right that new radios were needed to get the intermediate 50/25kHz channels but that was the only reason they were needed. Many airfields stayed on the old 100/50kHz channels for a long time and everything worked just fine. Again, this isn't possible with a fully implemented move to 8.33kHz, especially with the elephant in the room that is spectrum pricing (see my original post).

The cost (to aircraft owners) of implementing 8.33kHz could be spread over time in just the same way that the cost of moving to 50kHz and then 25kHz was spread over time - by sensible spectrum management. The combination of spectrum pricing and the UK tendency to implement EU legislation in full and without question creates a perfect storm... and a lot of unnecessary cost. A further point is that the life expectancy of radios was far shorter back in the days of 50kHz channels and, especially, in the (largely valve) days of 100kHz channels. So kit was being replaced more often anyway.

As an aside, it's worth noting that because of the need to retain 25kHz channel capability, e.g. for 121.5MHz, the actual number of channels created by this change is not trebled as you might think. It is in fact somewhat less than double what we had with 25kHz. A further point if interest is that this is the end of the line (for AM at least). There is no possibility to reduce channel spacing further without going to a different modulation method.

[The Westmorland Flyer]

One would like to think that whoever manages frequency allocation will keep that technical fact in mind (for a while anyway).

And this really is the nub of the issue. There are two key reasons why this won't happen without a concerted outcry from us aircraft owners.

1. The CAA will, left to its own devices, fully implement the Eurocontrol directive, despite the fact that the directive permits local amendment. It will, in short, pull another Part-M on us (Part-M is the EASA continued airworthiness directive, implemented, in full and without question by the CAA. It added several thousand pounds per annum to the cost of C of A aircraft maintenance for no discernible benefit. Other countries either didn't implement, or waited until a less draconian requirement emerged. By then it was too late for us).

2. The pernicious effect of the tax heist that is Spectrum Pricing in the internationally protected airband. This will encourage airfields, that otherwise had no need to, to switch to 8.33kHz as soon as they can, hastening arrival of the problem.

[R Perry]

No one seems to have mentioned it yet on this thread but the Dittel KRT2 8.33 radio seems excellent value at £999 inc VAT. I have had a Dittel for over 20 yrs in our syndicate plane.

[Mick Bevan]

Hi all,
I stand to be corrected but why, if this is a compulsory requirement of Europe, is it not being subsidised by Europe? As an airline person, I know that the cost of retrofitting airliners and CAT for 8.33 will simply be borne as a cost to be offloaded onto the passengers in the long run or as a reduction of the airline's tax bill by the accounts dept. Despite any bluster you may have heard from the airline industry, they will simply toe the line and change the equipment, as they have done with every other piece of kit that has been required to be changed or added, because they know that ultimately, someone else will pay for it. Airlines change or swap out pieces of aircraft every single day of the week at huge cost, either to comply with ADs or SBs or because kit is rubbish and unreliable so this is nothing new. An example would be Airbus IDGs at Eu80,000 under pool exchange......... If it were a piece of farm machinery or a requirement to do something with land or to get rid of a toxic pesticide, that Europe suddenly decided was compulsory, the farmers (many of whom are LAA members) would immediately take steps to ensure that their representative organisations and their local MPs/MEPs would lobby the EU intensely until the required action was either knocked on the head, deferred as unnecessary or else paid for by the EU taxpayer or written off against tax. Why is this not being done for the compulsory imposition of expensive radios? I'm not good on EU law but I am given to understand that if they impose something on you, then they must either compensate you or subsidise it. Can anyone clarify this?

regards
Mick Bevan

[Derek]

Hi Mick et al.,

8.33 has been compulsory in airliners for at least 10 years now. Lower level airspace/GA was left out of the conversion until now. I don't expect any noises from the higher end of aviation as they already have the newer radios.

As regards the tax/cost implications I'm sure if you use your GA aircraft for business then some tax relief would be available but probably not for our permit end of the market.

Derek Doyle
026153

[Rob Swain]

Despite any bluster you may have heard from the airline industry, they will simply toe the line and change the equipment

There are several reasons why they will do so:
As you say, they will pass on the cost.
In the grand scheme of things a few grand on radios per plane is really very small beans for them.

You did miss the most important one, though.

They will do it without complaint because they are the ones that want the extra frequencies!

Seeing as this is ultimately airline driven, and for their benefit, surely they should be subsidising our replacement costs!

One can but dream!

[Jon Leigh]

One question that has not been put to date is:
When we change the radios in our aircraft, as we will have to change not only the radio but also the design of the radio stack, will this require a minor mod application in addition to the cost of the equipment?
If there is a mod charge, as this is a change being forced on us, with as it has been stated, no obvious increase in safety would the LAA be able to reduce or waive the cost?

Jon Leigh

[jangiolini]

Its very simple for me! I am just going back to non radio!! Safety be damned I am wondering what is involved in fitting narrower filters to the microair radios and the likes!! I have fitted them to my Amateur radios in the past with varying results so it should be possible! I also seem to recall sending an Icom A200 in for repair and for a very nominal amount they fitted filters suitable for 8.33 £10 or so. It can be done maybe we need to force the manufacturers hand a little.
John.

[Chris Martyr]

We can sit around picking the bones out of the politics of all this until the cows come home , but it still doesn't alleviate the fact that by 2017 we are all going to have to be 8.33khz compliant. [ or NORDOs]

What we should be concentrating on is what John has mentioned . I.E. the most painless way of achieving this. Handheld radios with 8.33khz bandwidth spacing are available now , but of course are approved for ground use only , and if we were to have our currently used handhelds altered to 8.33khz , would they still be legal for use ?
If the Feds could be pressured into allowing a concession for PtF Day/VFR types to use handhelds, it would cure many grass-roots flyers problems instantly. OK , it probably wouldn't help the cause for those who choose to go european touring , but it would certainly be an option for classic/vintage types not to mention our weight-shift brothers.
Otherwise , we are going to see a proliferation of NORDOs appearing, which in itself is not a dangerous thing , but if one is in the circuit at somewhere like Popham, which accepts both , it is preferable if you can hear them as well .
I am sure that our capable ambassadors within the LAA are probably doing a fantastic job already of making this rather irritating and unnecessary task as pain-free as possible.
Although, I would be interested to know how those well known EU Ignorers , the French are going to tackle this.

As a footnote ; Funny how the Americans are still getting by with 25khz bandwidth spacing.
Guess it's down to the small amount of aircraft movements out there