Primarily for general aviation discussion, but other aviation topics are also welcome.
By cockney steve
FLYER Club Member  FLYER Club Member
#1516279
Back about 1977, i did a trade-show in Burnley. Customer from Accrington walked in with what appeared to be a hand-held Walkie-talkie.
We paused business, whilst he spoke to somebody who was about 8 miles away and explained that he would "lose" the contact when the other "Ham" drove into a valley.
As a nosey, inquisitive type, I asked a lot of questions, as he was the first "Ham" I'd knowingly met.
He said the Transmit power was 1/4-watt and I questioned it's practicality. He assured me, that power was sufficient for "line of sight" comms and suggested that, should he be standing on Dover's white cliffs, he could happily converse with someone in Calais....I had no reason to doubt his word.
In those days there were a lot of illegal AM American CB's about , which were several watts output. He assured me, given suitable atmospherics, the operators could converse with other units actually in America.

It's discussions like this where we really miss the wisdom of Keef. :cry:
#1516285
cockney steve wrote:..He assured me, that power was sufficient for "line of sight" comms .., given suitable atmospherics, the operators could converse with other units actually in America.

It's discussions like this where we really miss the wisdom of Keef. :cry:


Indeed

HF propagation (or failure thereof) is a wonderfully complex and fascinating subject. I have never been a civil-licensed 'amateur', but have at several times in my various employments had to be professionally dependent on HF. Most interesting (both challenging and allowing amazing distances at low power) was in Northern Canada at times of high Auroral activity. The conventional 'cut-off' of HF-and-below over-the-horizon propagation of 30 MHz is fairly arbitrary (but convenient for CCITT-compliant regulation). Analogous effects are often available well above that, and conversely may fail well below it.
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By Paul_Sengupta
FLYER Club Member  FLYER Club Member
#1516291
VHF line of site propagation is power dependant but if you imagine your signal spreading out as it gets further from the antenna, higher powers get proportionally less range. A quarter watt may very well get you from Dover to Calais with a sensitive receiver under normal conditions but not an awful lot further. You'd both have to be standing up on the cliffs otherwise the earth would get in the way.

However, there are conditions like tropospheric ducting (or...see below...sporadic E) which can take VHF further than is normally possible. I once, from the top of a tower block in London, spoke to a radio ham in Germany through a Belgian repeater (so my signal was going as far as Belgium, but so was the German chap's) using 150mW into a little "rubber duck" antenna from a handheld. It was foggy all across Europe - high pressure and inversions cause both ducting and fog.

Back in the sunspot high of 1980/1981, we could indeed talk to the US on a standard CB with a good aerial, but that was usually on SSB with about 12W peak power. Occasionally it worked with 4W AM. It was better with a higher power linear amplifier connected though, say 30W! :D

kanga wrote:Analogous effects are often available well above that, and conversely may fail well below it.


If you Google "Sporadic E" you can see that the E layer of the ionosphere can refract radio waves at VHF frequencies.

Or just click on the Wiki link...

HF ionospheric propagation ("bouncing" signals off the ionosphere) depends on a lot of things, but mostly the sunspot cycle and time of day. You'll get higher frequencies being propagated during the day. Google "maximum usable frequency".
#1516538
Bathman I feel your pain :(

I find my self in the same position PA28-140 with Narco MK12D nav com and CDI having went through the the same pricing excersise there is no way I can spend half the value of the aircraft on new nav com kit.

Discussed the options with the nice chaps at Mendelssohn's and they suggested leaving existing kit installed and fitting an Icom IC A220T. Just need to see if I have the panel space to accommodate an extra box.

Noted a sujestion earlier in this topic to use a handheld is this an option in a C of A type.
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By ThePipster
FLYER Club Member  FLYER Club Member
#1576098
ADIRU777 wrote:A plea to all of you wonderful experts out there :D

Please forgive the thread hijack and drift. I've tried searching various threads and posts but can't find a 'definitive 'answer...

Does our group have to remove our trusty (?) KX155 NAV/COMM when we install our new 8.33 capable COMM or can we keep the KX155 installed to use only the VOR capabilities?

Would marking the old 25khz COMM section 'INOP' be sufficient or do we have to have that deactivated?

Many thanks for any up-to-date info, pointers and opinions.

HNY



Did anybody come up with an answer to this?

Pipster
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By wigglyamp
FLYER Club Member  FLYER Club Member
#1576174
You can legitimately keep the KX155 and the Com side is limited to those frequencies retained for use on 25kHz such as 121.5. The nav side is still fine to use.
You can't de-activate the Com side as there's only a single circuit breaker powering both sides of a KX155
You only need a single 8.33 radio to meet the requirements of UK AIP Gen 1.5-11 unless you're a commercial operator flying on an AOC .
By riverrock
FLYER Club Member  FLYER Club Member
#1576175
You can leave 25kHz radios installed - so long as you only use them to contact stations which are still using 25kHz spacing (such as 121.5).
See http://www.caa.co.uk/General-aviation/A ... Hz-radios/ under "Continuing to use a 25kHz Radio"
CAA wrote:IR 1079/2012 states that from 1 January 2019, all ground services will be operating on 8.33 kHz channels.

Ground services across the UK will be converting to 8.33 kHz channel spacing at different dates throughout 2018, mostly driven by their annual licence renewal date.

If a ground service is still using a 25 kHz frequency then you can still communicate with it using a 25 kHz radio. Once a ground service has converted, aircraft must utilize an 8.33 kHz capable radio to communicate with it.

In practice, you can only continue to fly with just a 25 kHz radio if throughout your entire flight you only need to communicate on 25 kHz frequencies. Note, you must check regularly to confirm that your ground services have not converted. The CAA expects that most ground stations will have converted well before the end of 2018.

After 1 January 2019, use of a 25 kHz radio will very restricted, principally to only the emergency frequency of 121.5 MHz.