Primarily for general aviation discussion, but other aviation topics are also welcome.
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By Marvin
#1516183
riverrock wrote:We don't use the memory or intercom, and have it set on 25kHz mode so I don't know how fiddly its going to be once we have to change.
So not really much help in your decision!


I've just changed mine to 8.33 working. it's done through the set-up menu which you push a couple of buttons to get into on power up - manual explains. Relatively easy to do.
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By G-BLEW
#1516295
cockney steve wrote:Am I missing something? Isn't every 3rd 8.33 channel a 25 K Hz one as well?......Or have the frequencies been offset to force abandonment of "old " 25 K Hz kit?

Anybody? pretty please?


Yes - how would you select 124.485 or 119.015 on a 25 kHz set?

Ian
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By Paul_Sengupta
#1516299
Yes, essentially every third frequency is a 25kHz frequency.

Problems will arise when they start allocating the four frequencies, two either side, up to the next 25kHz frequencies. Your receiver will suffer interference from these frequencies, or at least the two nearest ones.

Also older transmitters may not have the filtering to keep them strictly within the 8.33 "band".
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By stevelup
#1516301
cockney steve wrote:Am I missing something? Isn't every 3rd 8.33 channel a 25 K Hz one as well?......Or have the frequencies been offset to force abandonment of "old " 25 K Hz kit?


25KHz spacing is still available on 8.33KHz radios. It works like this.

132.025 is a 25KHz channel on 132.0250
132.030 is an 8.33KHz channel also actually on 132.0250
132.035 is an 8.33KHz channel on 132.0333
132.040 is an 8.33KHz channel on 132.0416
132.045 doesn't exist
132.050 is a 25KHz channel on 132.0500
... and so on ...
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By Flying_john
#1516344
Our Funke 833 was very professionally installed too - I did it !. So I know there are no mounting screws that go into the case at all. All the mounting is done with 4 machine set screws through a plastic protrusion either side of the front panel. I have the rectangular version not the circular version. These four screws go straight into the threaded panel captive nuts.

I hope its not a "no fault found" because then it makes you start wondering what could be wrong. I measured the input supply, checked the earth, initially thought it may be RF , but it does it even before you transmit. Its worked fine for 5 months - so I hope they do find an actual fault.
By riverrock
#1516352
Ours went back and forwards a few times - it appeared to work on a bench but failed pretty soon after re-installation in the aircraft. Then it failed when on a bench too. They seemed to fix it, but the fix only lasted a few weeks. Then it was fixed properly - haven't had an issue in a year.

Hopefully now that the same issue has happened a few times to others (like myself), it will be a standard fix for you.

On the spacing - I didn't mean to cause confusion. The fiddly comment is because we have left ours in 25khz mode till we start finding stations using 8.33 spacing, to reduce the amount of knob spinning to get past the 8.33 channels. Therefore I don't know how the extra knob twiddling will affect usability. I'm sure we'll soon see (doubt it will be much of an issue).
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By Kittyhawk
#1516467
This unit from Air Avionics looks interesting. It can be split mounted like the Trig and the display looks good. It can also control their Mode S transponder from the same head, which saves on panel space. I spoke to the factory last week and they are awaiting final approval and hope to have it on the market late spring. Cost is comparable with Trig etc and I understand LX Avionics are the UK dealer.
By riverrock
#1516474
Yeah - I contacted them too.
Looks like an excellent unit at a good price (did they say the output power?)
However they have a huge pre-order backlog apparently - meaning you aren't likely to get one before 2018!
By cockney steve
#1516509
Thank you to everybody who replied....by coincidence, there is a "Farnborough radio" thread running today, and many of the same respondents have made this even clearer.

AIUI, now, 25 Khz spacing has a coarse, nominal frequency, whereas, as the 8.33 channel is much narrower, so it has to be much more accurately defined , meaning the corresponding 25 Khz band has around 2/3 "empty" when used for 8.33...but the 8.33 falls in the "empty " area.

Am I getting it?
By riverrock
#1516534
In simplistic terms, the signal has a fixed carrier signal and two side lobes which contain the audio info
Image

If using an 8.33 spacing, that carrier needs to be in the middle of that spacing, or its side lobes will affect other channels.

If using a 25kHz spacing, there is more flexibility, - that carrier can be within a wide area in that spacing.

The side lobes are mirrors of each other, so to get the frequency bandwidth required to transmit sound, you need to multiply by 2 the maximum allowed audio frequency.
So 8.33kHz spacing means the maximum audio frequency possible is 8.33/2 = 4.12kHz. Generally the filter is 7kHz wide, so only 3.5kHz.

Human voice spectrum:
Image
But with the key vowels, which makes speech intelligible here:
Image
So its possible to cut off some of the top of the full spectrum and still have intelligible words. Music might not sound good, and a high soprano singer might get cut off, so perhaps listening to classical music over airband wouldn't be the best, but speech still works.

The 25kHz spacing allows for old transceivers to not be accurate with their transmitting frequency yet still be picked up.
It is also used by some wide area services (D&D, Scottish Info, London Info, Farnborough North etc) - they transmit the same thing at different points within that spacing, far enough apart that the side lobes wont interact. Eg Scottish info's Craigowlhill TX/RX site operates on the spot frequency of 119.875mhz, Lowther hill operates on an offset of -7.5khz and Windy head on an offset of + 7.5khz. So all sites transmit within the same 25kHz frequency, but if you're high enough up to pickup multiple sites, they shouldn't interfere.

So your radio must be able to switch receive filter between 8.33kHz spacing and 25 kHz spacing, or you wouldn't be able to pickup the wide area transmitters or you will get interference between different 8.33 kHz channels.

Does all of that make any sense?
cockney steve, T67M liked this
By Highland Park
#1519022
For those of you who've had an 8.33 radio fitted only, not part of any other refit and not a permit aircraft, out of curiosity how much has the installation cost?

It's been suggested that we will need a new antenna, possibly new cabling etc for the Shiny Colt, which being an Annex II aircraft will probably increase the cost quite a bit.

Thoughts appreciated...
By riverrock
#1519027
I suspect there are a lot of variables.
If it's pin compatible, and going in the same place, installation should be:
1. Unscrew and disconnect old one
2. Unbox and place new one in hole.
3. Screw in and connect new one.
4. Do any required setup on new one (intercom on/off etc)
5. Test
6. Paperwork ( including weights and balance update)

However few installs would be that easy.
Our previous install cost £2000 labour, but that included new intercom, rewire, removal of lots of surplus equipment and wires, creation / fitting of blanks due to all the holes left!