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HelicopterBergen R/C Helicopters › dean/fma antenna
12-12-2004 02:33 PM  13 years agoPost 1
charger

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Spencer MA.USA

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Question for fma copilot user's
This is on a new Bergen intrepid gasser with boom ext for camera ship use. The dean's instuction say's cut the receiver antenna wire leaving 4" to 10" tin and solder.
The fma8 copilot manual states you may cut the antenna as short as 18" with out de-tuning the receiver.
This may seem like a silly question or I'am just missing something ,but I rather be safe than sorry on flying.
Please advise
Thank you

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12-12-2004 03:37 PM  13 years agoPost 2
Al Magaloff

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The base loaded Deans actually puts the length back.

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12-12-2004 03:38 PM  13 years agoPost 3
timid1

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NE WI, USA

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Ditto
Al is correct, as always.

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12-12-2004 05:18 PM  13 years agoPost 4
wolfdad

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Southern Maryland

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Ok, I am not familiar with the FMA FS8 copilot and had started to answer your post based on what my experience has been with antennas. Then, I thought that, perhaps in my ignorance of the FMA copilot, there was something I had missed. So, I wandered over to the FMA site, pulled down the manual and read a bit.

Not sure where the 18 inches comes in and that would definitely detune a radio (talking 72MHZ here), however I use the Revolution base-loaded whip on my Intrepid and the instructions say to measure and cut the receiver antenna wire exactly four inches from the receiver. This is based on the fact that 39 inches (the length of a standard 72MHZ wavelength) is duplicated with four inches of antenna wire and the base-loaded whip (the base-load representing the balance of 1 wavelength). For a quick explanation, the receiver looking at the antenna for a signal coming in must see one wavelength for the best signal to be accepted. Anything more or less and you start to have what is called a "mis-match" in impedance or resistance and the full strength of the signal will not be received and range will either be degraded or lost. This holds true for both reception and transmission although transmission is a bit more critical and, in higher power transmitters at HF frequencies, this can actually generate a dangerous situation.

Bottom line here is that anything less than a 39 inch antenna or a base-loaded compensated antenna for the specific frequency being used will result in some loss of signal and range at the receiver. We all know that there is some trade-off as evidenced by a car radio receiver. Obviously the antenna for an auto radio is not tuned for just one station but for a band of stations, so, depending on the frequency of the station, the antenna will be either more or less receptive. Our radios are single frequency transmitters/receivers, therefore there need not and most certainly should not be any trade-off. Personally, I advocate with my fellow flyers that if, their antenna gets cut, worn or damaged in any way, that it be replaced and for less than $3, that is insurance well worth buying.

Enough said about the dynamics of wavelengths. Bottom line is that anything less than 39 inches or a compensated base-loaded antenna tuned for the specific frequency represents a mis-match and reception will be degraded. Yes, your receiver will still probably receive some signal, however, in our hobby, any signal degradation is unacceptable. I couldn't find the reference to 18 inches, however there must be an alternative explanation. FMA Direct is a well-known, well-respected RC hobby company, so I am at a loss on this one.

Also, interestingly enough, I have flown both Dean's and Revolution's base-loaded whips and, personally I prefer the Revolution. The Revolution instructions give a definitive 4 inches of antenna while the Deans says between 4 and 10 inches (reference the above dissertation on wavelenth propagation). And, yes they do, in electronic terms, "put back the length," however they put back precisely the length they told you to remove, so draw your own conclusions. One other tip I might add is that I strongly recommend that the joint between the receiver and whip be soldered and covered with heat shrink. I was the victim of not soldering that connection and paid rather handsomely for that mistake.

wolfdad sends...

"There are those who have...and, those who will" IRCHA #2117, AMA #70068, Turbine Waiver #105

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12-12-2004 05:25 PM  13 years agoPost 5
Al Magaloff

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Wolfdad, I always cut to slightly more than four inches, because I don't use the connector, but prefer to solder and shrink tube method. This allows me to uninstall and re-install if needed. I don't think an inch will make a big difference in range. I did question that 18" thing too.

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12-12-2004 05:31 PM  13 years agoPost 6
charger

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Spencer MA.USA

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Thanks guy's

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12-12-2004 05:42 PM  13 years agoPost 7
timid1

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NE WI, USA

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one inch not making a difference!!!

Sorry, couldn't help myself!

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12-12-2004 05:43 PM  13 years agoPost 8
charger

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Spencer MA.USA

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The 18" is on page 10 of the intall section of the user's guide. I don't now if they stating the 18"if you don't add a whip antenna or does it still needs the 18" because of the fma built-in scanner progam?. There is a lot of gray area's in manual that state something with out explaning why or how too correctly.
Thanks again

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12-12-2004 05:55 PM  13 years agoPost 9
wolfdad

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Southern Maryland

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charger,
I will go back and look, however it sounds a bit strange to me. You might want to contact the folks at FMA and see what their explanation is. Also, be sure to do a thorough range check after this installation. I am fairly well-versed in the tron world and these instructions even had me scatching my head....something else that FMA might need some feedback on.

wolfdad sends...

"There are those who have...and, those who will" IRCHA #2117, AMA #70068, Turbine Waiver #105

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12-12-2004 07:17 PM  13 years agoPost 10
charger

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Spencer MA.USA

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I thought the same thing, that I would call FMA monday and see what they say before any cutting and soldering is done.I will post there comments and answers so others will know in the future
Thanks

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HelicopterBergen R/C Helicopters › dean/fma antenna
12-14-2004 08:31 PM  13 years ago •• Post 11 ••
charger

rrApprentice

Spencer MA.USA

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Called FMA and talked with howard the tech -man.He stated that FMA has only tested the fma8 copilot system with the azarr antenna and had pretty good results with it,and they snipped the the receiver wire down to about 1 inch and then solder it.He also stated that this don't mean the dean's won't work just as good, but what ever you do or use make sure you do a complete range check

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12-14-2004 11:59 PM  13 years agoPost 12
Al Magaloff

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Never heard of the azzar antenna, but his advice sounds reasonable.

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12-15-2004 03:36 AM  13 years agoPost 13
wolfdad

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Southern Maryland

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charger/Al,
New one on me as well. Did he say where the 18 inches came from? And, charger, your recommendation on a thorough range check is well-founded any time you make changes with the antenna....or for that matter, every time you fly.

Good luck with your co-pilot.

wolfdad sends...

"There are those who have...and, those who will" IRCHA #2117, AMA #70068, Turbine Waiver #105

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HelicopterBergen R/C Helicopters › dean/fma antenna
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