Question for aircraft comms engineers.

[magpienja]

Hi all....I am a licence UK radio ham.....on off over the years I have enjoyed listening to trans atlantic HF radio comes....not very busy now due data comms unfortunately.

Often wondered....what sort of RF power out a typical Airliner has??

Most of our off the shelf HF radios are 100w.

[dixi188]

If I remember correctly the Collins 618T HF TxRx was 125 Watts AM and 400 Watts SSB. This was the standard HF kit on many aircraft in the 1960s, '70s and '80s.

[magpienja]

Thankyou Sir.....can you remember...did they have a separate Antenna Tuner ATU....I remember a tuning sound often heard on the frequency.

I suspect todays HF kit has auto antenna tuning.

[happybiker]

Yes the 618T did require a separate ATU. The following link provides some general info but lots more available if you google Collins 618T. https://www.bing.com/ck/a?!&&p=7b20ab08939f6082JmltdHM9MTcwOTI1MTIwMCZpZ3VpZD0wNzkzMDY5My 01OTQ3LTY5YmUtM2VjZS0xNWNjNThmYzY4MDEmaW5zaWQ9NTIzNg&ptn=3&ver=2&hsh=3&fclid=07930693-5947-69be-3ece-15cc58fc6801&psq=collins+618t+radio&u=a1aHR0cDovL3d3dy5yYWRpb21hbnVhbC5pbmZvL3NjaGVtaS9TdXJwbHVz X0NpdmlsL0NvbGxpbnNfNjE4VF9TcGVjaWFsX0ludGVyZXN0X0dyb3VwLnBk Zg&ntb=1

[magpienja]

Thankyou for that link....very interesting.

[MAC 40612]

Thankyou Sir.....can you remember...did they have a separate Antenna Tuner ATU....I remember a tuning sound often heard on the frequency.

I suspect todays HF kit has auto antenna tuning.

Most modern airliners still have a separate ATU and this is normally placed as close to the antenna as possible, which can be a bit of a pain when they fail. On the Boeing 777, for example the ATU is located high up on the fin behind an 'access panel' [well that's what Boeing call it....I would just say it is a normal non-structural panel] and it is definitely not 'quick access' as it has about 250+ countersunk screws in in that have to be removed to get the panel off before you can access the [two] ATUs that are at the top of the fin.

[ve3id]

Yes the 618T did require a separate ATU. The following link provides some general info but lots more available if you google Collins 618T. https://www.bing.com/ck/a?!&&p=7b20ab08939f6082JmltdHM9MTcwOTI1MTIwMCZpZ3VpZD0wNzkzMDY5My 01OTQ3LTY5YmUtM2VjZS0xNWNjNThmYzY4MDEmaW5zaWQ9NTIzNg&ptn=3&ver=2&hsh=3&fclid=07930693-5947-69be-3ece-15cc58fc6801&psq=collins+618t+radio&u=a1aHR0cDovL3d3dy5yYWRpb21hbnVhbC5pbmZvL3NjaGVtaS9TdXJwbHVz X0NpdmlsL0NvbGxpbnNfNjE4VF9TcGVjaWFsX0ludGVyZXN0X0dyb3VwLnBk Zg&ntb=1
Oh yes, that antenna tuner. If it was the one I saw once, it was quite a thing. My first job out of high school was working at the KW Electronics factory in Crayford, Kent, where I aligned and tested brand new ham radio sets off the production line for sale. The engineers that did repairs quite often got some commercial gear in, and one day they had a Collins aviation transceiver with ATU. To test it out, they strung some magnet wire across all the wooden benches in the lab (after we got off them, thankfully) and powered up the Collins. Key down, there was way too much current for the wire to handle, and you could see current nodes getting red and eventually melting the wire. the new antenna length cause a high SWR, and then you heard the 'eyee euew errrr' of the motors in the antenna tuner unit correcting that, only to be followed by more melting of wire until it was too short and they stopped the test! (Another ham here, now living in Canada, as well as examiner for the amateur and pilot radio certificates).

73

[TURIN]

Is the ATU what is now known as a coupler?

[magpienja]

Most modern airliners still have a separate ATU and this is normally placed as close to the antenna as possible, which can be a bit of a pain when they fail. On the Boeing 777, for example the ATU is located high up on the fin behind an 'access panel' [well that's what Boeing call it....I would just say it is a normal non-structural panel] and it is definitely not 'quick access' as it has about 250+ countersunk screws in in that have to be removed to get the panel off before you can access the [two] ATUs that are at the top of the fin.
Interesting....I presume that the 777 as most modern aircraft....that the ATU will be fully automatic in operation.
Also can I ask.....what do modern air craft use for a HF antenna....as you will know....generally they need to be long to cope with the long wave lengths of HF frequencies and the older a/c may have a long wire from the top of the fin to the forward fuselage.
You see nothing like that now.....so where an earth is the HF antenna on the likes of a 777.

[magpienja]

Oh yes, that antenna tuner. If it was the one I saw once, it was quite a thing. My first job out of high school was working at the KW Electronics factory in Crayford, Kent, where I aligned and tested brand new ham radio sets off the production line for sale. The engineers that did repairs quite often got some commercial gear in, and one day they had a Collins aviation transceiver with ATU. To test it out, they strung some magnet wire across all the wooden benches in the lab (after we got off them, thankfully) and powered up the Collins. Key down, there was way too much current for the wire to handle, and you could see current nodes getting red and eventually melting the wire. the new antenna length cause a high SWR, and then you heard the 'eyee euew errrr' of the motors in the antenna tuner unit correcting that, only to be followed by more melting of wire until it was too short and they stopped the test! (Another ham here, now living in Canada, as well as examiner for the amateur and pilot radio certificates).

73
Would loved to have seen that VE3

[TURIN]

Interesting....I presume that the 777 as most modern aircraft....that the ATU will be fully automatic in operation.
Also can I ask.....what do modern air craft use for a HF antenna....as you will know....generally they need to be long to cope with the long wave lengths of HF frequencies and the older a/c may have a long wire from the top of the fin to the forward fuselage.
You see nothing like that now.....so where an earth is the HF antenna on the likes of a 777.
Usually in the leading edge of the fin. Known as a notch antenna. Please don't ask me what that means or I'll start to whimper. 😁

[dixi188]

I see the 777 is no different to the old 707 regarding access to the ATU. The 707 usually had one in the fin and one in the stbd. wing tip.
I also remember Sunair HF sets that were often fitted to smaller aircraft like Islanders for ferry flights. They had a TR and an antenna coupler, they used a trailing wire antenna that had to be tuned by varying the length. The controller had a SWR meter to use when tuning.
We had one in an Electra, with a fixed wire antenna, for a transatlantic ferry flight but it was next to useless. Fortunately the VHF coverage at high latitudes was very good so we didn't need the HF.

[happybiker]

I also remember Sunair HF sets that were often fitted to smaller aircraft like Islanders for ferry flights. They had a TR and an antenna coupler, they used a trailing wire antenna that had to be tuned by varying the length. The controller had a SWR meter to use when tuning.

Blimey, I had almost forgotten about Sunair HF sets. I recall spending a few hours setting the Antenna Coupler on new installations on Shorts Skyvan aircraft using a Bird Thruline Wattmeter to achieve the optimum VSWR for each channel. On one occasion I was still holding the clip to adjust the inductance when I pressed the transmit button which resulted in a nasty RF burn on my forefinger that took several weeks to heal properly. Painful lesson learned!
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[magpienja]

Great story....yes RF burns are nasty arnt they....did it leave a little on your finger.

Only had one RF burn....neat little hole....took a while to heal.

Happy biker...are you?....I ride a 2020 Triumph T100....and an old Bantam.

[happybiker]

Yes a nasty little hole in the finger.
Yes, a Hinkley Triumph Thunderbird 900

[magpienja]

Yes a nasty little hole in the finger.
Yes, a Hinkley Triumph Thunderbird 900
Arrrrr a fellow Triumph Owners....I sort of already knew....great machines.

You tried the factory tour?

[dixi188]

I managed to avoid the HF burns but saw an apprentice get burned when working on some piece of kit on the bench. He was not happy.
I had old Triumphs, Tiger Cub, T21, Tiger 90 and then a new Tiger 750 in 1980. I stopped riding when I started a family in 1984.

[magpienja]

I managed to avoid the HF burns but saw an apprentice get burned when working on some piece of kit on the bench. He was not happy.
I had old Triumphs, Tiger Cub, T21, Tiger 90 and then a new Tiger 750 in 1980. I stopped riding when I started a family in 1984.
Cant keep a Triumph Man down....I only got into bikes aged 63.....started on an old B175 BSA Bantam still use it......used that for 4 years till I though I was ready for a bigger big.....love my Triumph.

[happybiker]

No I was planning to go on the factory tour a few years ago but work got in the way:sad:

[mnttech]

I see the 777 is no different to the old 707 regarding access to the ATU. The 707 usually had one in the fin and one in the stbd. wing tip..
Our ex Pam Am and American 707's had two couplers at the tip of the tail and a LARGE RF relay that swapped between TX on #1 or #2. The coupler controller sat in the E&E next to the TR.
Interesting to read the number of 707's that had the one on the STBD wing tip.
I think we had both 618Ts and one or two had the 628T with the adapter rack to fit where the 618T was.

Our CV-990's had Collins S4's, coupler in the tail, controller next to the TR.

I don't remember our L188 having HF.

[magpienja]

Our ex Pam Am and American 707's had two couplers at the tip of the tail and a LARGE RF relay that swapped between TX on #1 or #2. The coupler controller sat in the E&E next to the TR.
Interesting to read the number of 707's that had the one on the STBD wing tip.
I think we had both 618Ts and one or two had the 628T with the adapter rack to fit where the 618T was.

Our CV-990's had Collins S4's, coupler in the tail, controller next to the TR.

I don't remember our L188 having HF.
Those HF antenna must have been quite short by the sounds of it.....make me wonder how effective there were....compared to the external long wire.....top of tail to the cock pit area.,