Powerful Aircraft VHF Radio

[Pelagic]

Originally Posted by bill good

A simple vertical whip on top of a wheel house? what is the installation going on? Bit hard trying to advise without knowing a bit more!!

Thanks again Bill....This is the fairly tight budget project I am involved with. Normally all these answers would have been well researched, but the radio was a last minute thing.

These early drawings show the structure but not the final mast design which is next on the production list as all the gear is here now

You can see we have many platforms to mount an antenna

[Wotname]

OK, time for some professional advice . Well, free internet professional advice anyway.

First, What Bill has said is pretty good so far.

Bear in mind that the A109 will have a 1/4 wave ommi antenna with a reasonable groundplane and a general aviation radio with a transmitter output of around 10 watts (often a Bendix King KX 155A or KY 196A or Garmin GNS 430W).

You will not need anything more than what the aircraft is using as anything more will then be limited by the aircraft system not yours. If you duplicate a similar setup as the A109, you will get the same performance envelope.

So I suggest a transmitter output somewhere between 7 an 12 watts and a 1/4 wave ommi antenna. Make sure the coax feed is not too long or use a low loss coax. If less than say 10 ft, then RG 58 will be fine, anything between 10 and 20 ft maybe RG 400 and over 20 ft, I would suggest at least RG 213 or RG 214.

The Icom mentioned earlier is a good starting point and any 1/4 wave antenna (centered around 125MHz) with a suitable groundplane will do. The groundplane should have a radius around 18 inches. Going by the pictures, you should have plenty of room to play with . You can make a simple whip for around $10 or buy one for any amount .

IMO, stay away from a high gain antenna - you won't get any advantage in the usage you describe and as others have said, can cause problems when rolling.

For the record, the aviation band is 118 to 136 MHz and maximum power is limited to 25 watts AM carrier power.

[svaletheia]

Note that having a handheld radio capable of AM communication on aircraft bands is perfectly legal without a license so long as you only use the aircraft bands for emergency purposes, as well. In nearly EVERY country there is an emergency exception for almost all normal voice frequencies, and in the US you are permitted to use any frequency at your disposal in an emergency.

However, in some countries it may be illegal to own a *dedicated* aircraft radio without a license.

I've considered getting a station license for aircraft comms as well, but like some other posters mentioned, most of the aircraft that are interesting to communicate with on a ship have marine radios already, and HF is definitely the way to go offshore. I may just pick up a cheap secondhand handheld aircraft radio as a backup.

Further NOTE: the VHF antenna for an aircraft radio is going to be very different from the VHF antenna for marine use because of the frequency difference. However the ground plane issues are exactly the same. Since a typical VHF works just fine on a boat, a 1/4 wave whip antenna mast mounted has a perfectly suitable counterpoise in the mast and shrouds themselves and shouldn't need ANY more groundplane than that. If anything, the takeoff angle is improved by the downward sloping shrouds, which is perfect for working the skies.

Don't worry about needing any further ground plane work - at those frequencies its just not necessary at all.

I'm a Amateur Radio Operator. Callsign KI1L.

[Pelagic]

Thanks Wotname.

You guys have helped me a lot to quickly get a handle on this.

I will have them order the Icom, A110-05 because it will fit in nicely and will do the job.

Here is my preliminary sketch of the mast layout before they play with the styling.

I will have them create a number of platforms and if I put the whip antenna on the upper spreader arrangements where I show antennae mounted up and down the cable run will be about 60 ft

Wotname, if I were to buy a good quality whip antenna to match this radio, any thoughts on what I should specifically order?

Cheers!

[Wotname]

Originally Posted by Pelagic

...............
I will have them create a number of platforms and if I put the whip antenna on the upper spreader arrangements where I show antennae mounted up and down the cable run will be about 60 ft

Wotname, if I were to buy a good quality whip antenna to match this radio, any thoughts on what I should specifically order?

Cheers!

Let's deal with the easy bit first, the coax:- For a 60 foot run, I would use LMR 400 or LMR 400 Ultra. The LMR 400 Ultra has a stranded center conductor so it is much more flexible but is about 15% more lossy than the solid center conductor LMR 400. However if you can't source it (or the connectors) then use RG 214.

Now for the harder question:- As for a specific ship type antenna, I am probably not your best man for advice as I am not up to speed with what is available (unless it is an airframe antenna ) - but I will have a go anyway.

Try an RF Industries GP3 which is essentially an airband 1/4 wave antenna with its own counterpoise but it might not be pretty enough for your application. Ground Plane Antennas | Wireless | RF Industries

If you wish to go for an airframe antenna then try either a Comant Industries CI 121 or CI 211. These are normally mounted (and grounded) onto an Al airframe. You might need a metal plate (groundplane) to mount them on. In the perfect world, this plate would be circular with a 0.6 M radius but the antenna could possibly be just mounted onto a significant bit of metal on the ships structure. Electrically these are the same antenna but have different styling.

COMANT ANTENNAS from Aircraft Spruce

Pilot Supplies, Avionics, and Homebuilt Aircraft Parts from Aircraft Spruce and Specialty Co.

Bill's suggestion of a DM C63-1/A antenna is also suitable but the Dorne & Margolin antennas usually significantly dearer compared to Comant Industries units - at least in Australia.

Svaletheia note about the counterpoise of the mast and rig of a yacht carries some weight and may apply also to a ship's superstructure. However I don't have the hands on experience of ship antenna systems to confirm the leap from a dedicated groundplane (which I know works) to just bolting it on to the ship's superstructure (which only might work).

I will be around this weekend it you have any other questions but then I will be away on an oil rig for a couple of weeks and therefore out internet access.

[bill good]

Recommend you contact someone at Commscope see www.andrew.com. You need to consider placement of the aerial to prevent interference from each service. Attention to cable dress to prevent water ingression & water tight entry points all need to be addressed. Andrew supply a range of ground plane independent base station aerials & will do one for the frequency range you need. They supply a vertical element enclosed in glass & will make to suit the frequency range you need. (you may have to request what frequency you can have programmed into your radio from who ever is in control of spectrum management in the USA) What you are doing should be planned by experts. All the coax, connectors etc can be supplied by the above company. RFI may have product in USA but they also sell out here Andrew equipment as it is top line gear. The Cessna type is fragile by comparison but would work if mounted on that support system & provide with a ground plane if not metal.(Aviation & Comms has been my past) Now retired to work on my boat!! ps Given the task from a clean sheet, if there is only one heli involved & over water ops being undertaken, then I would have recommended the marine radio be installed in the heli. It works out here with the ship pilots, SAR aircraft & Coast Guard aircraft all come up on marine Chs & all sound very clear. It gives extra level of safety to the heli ops to be able to use Ch16 if needed. Yes it is more expensive but how much is being spend between that boat & heli?

[Wotname]

Additional note to fitting a marine VHF into an airframe.

Bill's comments are spot on but I must add that there are many many many POOR installations of of this type flying around and they give the process a bad name. I know because I have made a small fortune over the years bringing such installations up to scratch.

When installed properly, they work very well (as evidenced by Bill's experience) but there are some significant traps to be avoided. I can also say that many of the poor installations have been carried out experienced licensed aircraft radio engineers (even some of my colleagues) who don't realize what they don't know when it comes to fitting non-aviation comms into an airframe (especially helicopters). The problems lie in the significant difference in microphone requirements, vibration levels and the high noise environment in some airframes.

It would be significantly cheaper/easier to fit the airband radio to the ship rather a marine radio to an A109.

[hellosailor]

Pelagic-
With a little web searching you should be able to find charts of the radiation patterns from various antenna types. Whether they are ham, aircraft, marine...won't matter much, the radiation patterns for whip antennas will be similar, in the sense that as the gain increases, the radiation pattern goes from a sphere to a donut to a pancake.
When you see this plotted on a polar chart, you can get a pretty good idea of just how much gain you want--versus how that will impact the angle/distance of effective communications.
Of course, with all the real estate that you have available, it is also entirely rational to install two aircraft antennas (either with two radios or an antenna switch) so that you have "the long range antenna" and "the short range antenna".

[Pelagic]

Thanks Guys…

Wotname has confirmed what the local heli pilots tell me that the marine band VHF radios don’t fit and work well on smaller air frames because of ambient noise factors. (I guess that is why they are much cheaper and I am sure the USCG are fitting special ones...also SAR is a joke in this country )

That is why they want the yacht to have VHF Airband for ETA's and landing conditions... especially if the yacht is underway!

Hellosailor, I have looked at Google/ YouTube patterns and to be honest, all I got was a headache trying to figure out which antenna is best

There is nothing that beats actual experience when deciding whether 3, 6, or 9db is better for an aircraft flying at 8000ft, which the pilots tell me is their preferred maximum altitude.

This table shows the difference but actual experience will tell you the best compromise, so I was hoping to find a consensus here from the technical gurus here, before I confirm it with an unknown supplier

We will not be fitting 2 radio setups so I just want to try and get into the “Excellent” range with the proper cable and the right antenna for this application

[Wotname]

Originally Posted by Pelagic

..........

There is nothing that beats actual experience when deciding whether 3, 6, or 9db is better for an aircraft flying at 8000ft, which the pilots tell me is their preferred maximum altitude..............

Just to repeat: The A109 with have a 1/4 wave antenna with no gain and a ~10 Watt transmitter. This will give it a transmit range of say "x" miles.

There is no point with the ship going to a special high gain (and therefore directional) antenna trying to get a transmit range of say "2x" miles when the A109 will be far out of its transmit range of "x" miles.

Unless you want some "one-up-manship" between the captains of the ship and helicopter .

Hope it all works out.

[Pelagic]

makes sense..... Only as good as the weakest link....So can anyone hazard a guess at what would be the approximate range of the 109's 10w at 8000ft?

[svaletheia]

Plenty. 10W in line of sight should get you several miles of clear communication in most conditions into a 1/4wave. I run 50W into a 1/4 wave mounted on the roof of my truck on 144 MHz and on the ground, NOT direct-line-of-sight, bouncing through trees, around hills and valleys and such, I've hit contacts very clearly over 35 miles away at half power.

Over the water, you have a huge advantage over that situation. 10W into a clean antenna, radiating in nearly unobstructed air, you'll be in solid contact with aircraft at least as far and most likely well in excess of what I was able to do.

[svaletheia]

I again strongly recommend the lower gain antennas, 10W doesn't sound like much but its a very capable VHF rig when properly installed, especially out over the water.

And doubling the power does not double the distance transmitted, since the inverse square law applies. You need to quad the power to double the transmitted distance, so to increase your range by a factor of 2, you need to increase transmit power by a factor of four.

Running that backwards, it means your ability to transmit on 10W is only roughly half the effective range as someone with a 40W radio, not 1/4th the range.

Also, allow me to say something about iCom... their radios are quite literally some of the best out there, period. They are up there (and quite possibly exceed) the durability of Motorola's commercial gear - which has been known to literally stop bullets and keep working, from what I'm told. This is excellent gear and for the money you won't find better anywhere. I've used ALL major brands of comm gear. I personally highly favor iCom (although I have a few Kenwood rigs for technical feature-set reasons).

One of the best things about their radios, though, is that their voice quality on-the-air is typically rated as being incredible. The clarity of the voice transmissions is far superior to most other brands and the equal or better of any of them, in my personal (and general consensus as well) opinion. This alone gets you greater "effective range" out of the same xmit power as on the marginal conditions where you are pushing the range limit, the iCom is often the more intelligible radio. This should not be undervalued - as it can make the difference between a correctly received transmit and a misunderstood one in times of high stress.

From my personal experience, I would strongly suggest you not buy any other brand unless you have a very clear reason why you are doing so.

[hellosailor]

Well, with a 6 watt VHF and cheap antenna I can work a repeater mounted less than a thousand feet up and twenty miles away. Background noise and being heard over stronger signals will be an issue, but a 10W radio at 8,000 feet should easily have the same 20-mile range if you are in open water or someplace where there are no competing signals knocking it out.

Pelagic, if you got a headache, you should have stuck to the pictures. No, really, there should be simple polars out there someplace. Meanwhile, try this page from West Mainre:
The West Advisor: VHF Antennas

Scroll right down to the blue bar and graphic about gain and radiation patterns. A 3db gain antenna will work close in, a 6db gain antenna might have too low a radiation pattern to be used closeup, but could be useful IF you expect to be playing tag with the helo at ranges in excess of 20 miles, i.e. out at sea, or if they are coming in low for some reason. Quarter-wave vertical whips, encased in fiberglass, are typical 3db gain antennas. Rugged, inexpensive, and one that has a ground plane or radials at the base will outperform one that doesn't.
Don't let them cheap out on the cable, either.

[svaletheia]

Technically a 1/4wave antenna is 5.15dBi... and 3 dBd. But I'm just nitpicking.