Gash

Gash

Well Known Member
I will be installing a Garmin GTN-650 in a 14vdc system soon. I am unsure if I should go with the standard 10 watt transmitter, or if I should wire in a 14-28vdc voltage converter so that I can use the GTN-650's 16 watt transmitter option.

Why would I want 16 watts of radio transmit power? What are the practical operational reasons for going with 16 watts instead of 10 watts? Thanks very much.
 
If you are going to cross the north Atlantic Ocean get a 16w, otherwise the 10w that most everyone else uses is just fine. Jim
 
VHF signals are pretty much limited to line of sight. 10 watts is plenty, unless you fly in the flight levels (where you can see a lot further).
 
Even in the FLs, would 16 watts be necessary? It seems that with all the VHF repeaters the ARTCCs use, there shouldn't be any problem having enough signal strength at 10 watts to reach the nearest repeater. I could be totally wrong though--please correct me if so.

Oh, BTW, there will be no pond crossings in this RV-8. I wouldn't be able to carry enough piddle packs!
 
Woody, I can't help you with your transmitter question, but I just wanted to say that your avatar is certainly one to remember. Almost frightens me to look at it. I've a feeling it has something to do with a fighter squadron. You don't have to answer. ;)

P.S. Okay, I just did some surfing and got educated. 80th, and a Headhunter, huh? Glad to have you among us. Hope I can sleep with both eyes closed tonight.
 
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The higher power is nice, makes for a nice clear radio transmission, but I personally wouldn't install a converter (bulky, heavy, expensive) just to have the higher power radio.
 
Power increases vs range increases are not linear; they are exponential. Ex: to double range, you need ~10 times the transmit power. It's extremely unlikely that you'd be able to detect the difference between 10 & 16 watts, without sophisticated test gear.

Charlie
 
10 watts of transmit power is plenty.

With a 10 watt legacy GNS 430, I was able to still carry on a conversation just fine from near Enid, OK (Kansas/Oklahoma border) to a buddy who was getting ready to land at Eagle's Nest on the south side of D/FW metroplex. His radio is a Becker compact radio with only 7 watts output power.

I was at 10,500 MSL, which helped of course, but that's still an impressive distance to cover with a VHF aircraft comm radio. Both aircraft are equipped with the Comant bent-whip belly mounted antennas.

Your antenna is much more important than a few watts more transmit power.
 
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I just wanted to say that your avatar is certainly one to remember. Almost frightens me to look at it. I've a feeling it has something to do with a fighter squadron.
Click to expand...

Yep, you got it Don. It's the 80th Fighter Squadron patch, designed in honor of the head hunters in Papua New Guinea who during WWII helped a downed AAF fighter pilot avoid Japanese capture and get back to friendly forces unharmed. I flew with the 80FS (last century!) I never thought of it as a disturbing graphic, but I can see where you're coming from. Any depiction of a man with a bone in his nose will make you look twice!
 
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Thanks guys! Those are good points about power vs. range and antenna quality. I seem to vaguely remember these facts from a long time ago in college. It's nice to have experts here who can dredge up these important facts from the cold, dark unused corners of my brain.
 
Small physics correction: radio signals' power falls off like the inverse square of the distance,eg, 3 times further away would require 9 times more power, all other things being equal, to keep the same signal strength. Of course if the receiver is beyond the horizon no amount of power will help.
The square root of 16/10 is 1.26, so the best you could hope for is a 26% increase in range.
Previous poster is correct; if you want a stronger signal invest in better coax, connectors, and antenna. Many coax/connector/ antenna systems have a 3 dB loss, which doesn't sound bad until you realize that 3 dB corresponds to losing half of your power!
 
You need a certain amount of power, fair enough. 4W is supposed to be just fine provided:

You don't loose much power in your antenna cable. Keep that short and use good, low loss cable. You'd be surprised how much you can loose. 1 or 2 dB loss does not sound like a lot but it is.

Most important - the weak link is not the transmitter, not the cable but the antenna. The antenna and installation decides how far you are going to reach and in what direction your power is distributed. Your airframes shape and material with respect to the antenna location can have a great effect - usualy negative.

Lastly - do not forget that modultation makes range. A nice, powerful carrier means nothing if your intercom gets 20% modulation out of it. Modulation is as important as power - this decides how well your transmission will be readable when you get to the edge of your range.

Power can have negative effects - sensitive equipment in close proximity like EFIS systems, GPS receivers and be affected by strong fields.
The more power you have the more important correct installation becomes. Reflected power due to bad SWR can become an issue.

Rainier
CEO MGL Avionics
 
Just to add one bit to previous posters' points - it's a lot better to improve the performance of the antenna/coax system than it is to add transmitter power. Remember that substandard efficiency of the antenna system also affects your receiver performance - all the transmit power in the world won't help if you can't hear the reply.
 
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