Model Boat Mayhem
Technical, Techniques, Hints, and Tips => Radio Equipment => Topic started by: OMK on July 25, 2006, 03:40:47 am
-
A nice little gadget for testing the range of your transmitters.
http://www.keirle8122.fsnet.co.uk/gadgets/fsm/fsm.htm
This unit was tested on a new 27MHz AM Futaba Tx (shiny new antenna), then compared with a battered old 2-ch Futaba (manky antenna). It shown that the manky antenna had a reduced range in the order of some 50%. And to prove it wasn't a fluke, antennas were swapped. The battered futaba sprang to life. The new Futaba had around 40% less range.
Nice thing is, it will test any transmitter - AM or FM - on any UK R/C band... 27Mhz, 35MHz or 40MHz. (72MHz if you make a slight change at the coil.).
As the ad. man would say: "Still suffering with jittery servos?"
PMK.
-
Looks like a good circuit. I would not mind building one myself. I think there could be a market for a kit, if anyone fancied putting one together.
Neil
-
I've often wondered if the fact that our antennas become stiff (stop it) when trying to increase or decrease the length due to a build up of surface grime, would cause a lack of conductivity and thus shorten the effective length of the aerial and there fore the range.
Any thoughts ???
-
They probably need lubricating (sorry!) with switch cleaner to maintain optimum performance. Interesting point though, as I think we all tend to take TX aerials for granted and worry about the RX ones. I think I'll put some cleaner on my old sets anyway.
-
With radio frequencies there could be a small gap between two sections of the antenna, yet it willl still work as long as there is sufficient capacitance across the gap to allow the RF current to flow. It is worth keeping the aerial clean and lubricated, just to stop you snapping it when retracting.
Neil
-
Nothing wrong with using a 'field strength' meter but you do have to remember that it isn't telling you anything exact. It'll certainly give a 'relative' reading though. Relative to distance between transmitter and meter, sensitivity of the circuit, size of antenna/aerial, etc, etc. Change any of those variables and you change the readings (micro-volts/meter). It always helps to wear a red shirt when doing such testing. RF is not very sensitive to red...
- 'Doc
-
...yet it willl still work as long as there is sufficient capacitance across the gap...
Now you're being pedantic. How many people do you know actually using sloppy antennas?
True what you say though... in theory. But, in practice, that 'capacitive gap' which you mention would lead to all sorts of detrimental effects and highly unlikely that the signal would radiate at anywhere near its full potential.
Since most R/C transmitters have a series inductor in the antenna circuit, could it be that the added capacitance which you mention would pull the output from its resonant frequency, or a mismatch at the output driver stage?
I would assume that PMK is offering simple circuits in that it would allow most any person the opportunity to build - for all his components are of (his words) the bog-standard variety. He also makes mention of microprocessors on some of his pages. So reading betwen the lines, one is given the impression that he has already taken into account that some of you would not have the means or wherewithal to program such devices.
Nice site you have there, by the way. I am quite taken with your battery-balancer project.
Doc.
Variables and parameters are what make life interesting. Could the reason why my Futaba ceases to function on Modays is because Monday is the day I wear red panties?
-
Re miss Sinbad
The series inductor in the antenna only shortens the lenth of the antenna. change in lenth of antenna does not alter the Frequency only the VSWR "voltage standing wave ratio" or tuned lenth .this can lead to you blowing output of tx in severe cases.
some earley hi-tec had probs when used for long spells with ant down. Peter
-
Miss Sinbad,
I'm afraid I can't answer that from experience. I never wear red panties. ;)
And that's as far as I'm going with that! I have too much experience with red faces, My own mostly.
- 'Doc