Antenna too long

Being a 'ham' for nearly 30 years provides one with lots of experience with antennas.

The BEST antenna for ANY receiver frequencies well up into the VHF region ( 30-300Mhz) is the LONGEST piece of wire that can be strung up so that it does not get grounded. Hams regularly use 'long wire' antennas - 300, 400 , 500 feet long - even more!

For a transmitter, the reason for tuning the antenna is to convert maximum RF power into radiated power. If the antenna is not tuned or matched, then power is reflected back (SWR measures this). If the RF final amp cannot handle the reflected power, it will eventually smoke. The transistors used in ~most~ RC transmitters can handle 100% of the power reflected back - think no antenna screwed in - and do it forever since the transistor can dissapate the RF energy as heat.

And actually, I created a 'center loaded' antenna ! And it was not luck - center loading is commonly used to shorted even TX antennas with minimal signal strength loss.

Check your range with the TX antenna removed - should be about 40'. Now w>>Well, that contradicts everything I was ever told.

My Crazy 8 is a Cobalt 400 powered screamer with a 31" span. I had it up high enough - about 5 mistakes worth since it was the maiden flight - to get that rascal trimmed. A couple of times I lost orientation with it until I remembered 'dark bottom - light top'.

Never had any hint of range problem.

3/8" to 3/4" is more than enough diameter, and I 'tight wound' mine - which means the turns are touching each other.

It's a BIG plane if you can SEE it well enough to control at 1000' !

David

The style antenna used in RC TXs is a verticle antenna. Verticles MUST have a GOOD ground plane of the proper size to be properly tuned

- which RC TXs DO NOT HAVE and therefore CANNOT be 'highly' tuned.

David

Another factor to consider when measuring antenna length for a particular frequency is the velocity factor of the wire. According to the egg heads electrons travel at the speed of light in a vacuum but slow down in other conductors. The velocity factor of most copper wire is .65.

2c worth

antenna,

receivers,

exactly to

broadly

coupled

somebody in

plane

through

antenna

circuit,

resonate -

Wan scribed in :

never double them over rather cut it to half length if the plane is small, you won't be flying it so far away that it will go out of range anyway

swarf, steam and wind

-- David -:- the email address is real but not forever /"\

\ / ASCII Ribbon campaign against HTML E-Mail > - - - - - - -> X If you receive email saying "Send this to everyone you know," / \ PLEASE pretend you don't know me.

Depnds on wht you man by 'highly'

They are a lot more 'highly' tuned than RX.

I know. Ive built both.

Those were YOUR words, not mine........... go back and read your post.

David

Never double them over? And cut it to half length? Here's a quote from Dr.1 Driver;

"Not really. What he did was to create a base-loaded antenna. Base loads are EXCELLENT for receiving. IMO, he got lucky. The plane could as easily have crashed as flown well. "Don't fool with antenna length" is a good motto. Dr.1 Driver "

I was really looking forward to the simple solution of doubling them as suggested by Arne earlier in this thread. But I will wind the antenna around a piece of light balsa, installing it inside the fuse as I had said before.

I will of course do an exceptional range check just to be sure.

By the way, someone I know said all 72 MHz radio Rx have 41" antennae. If true, why does one small GWS Rx have 19", another GWS Rx have 39" and my Hitech Micro 555 have 42"?

Maybe we can fool with the antenna length of the receivers?

Hmm... Wan

Notice the range figures for that little GWS RX..... probably 300-500 feet.

The range test is the 'proof of the pudding' as the old saw goes.

David

snip

That has more to do with the fact that its electrically rather 'basic' than the slightly shorter antenna length. In Europe on 35Mhz the JETI lightweight receivers come with very short antennae, and whilst not full range, are a lot better than the aveage GWS parkflyer. They are more expensive tho.

TNP and David,

David, by range figures, did you mean range test or range check while on the ground or in the air at 300 t0 500 feet?

I had made a range test of the 72 MHz GWS Rx , 19'" antenna, ground level, Tx antenna collapsed at about 200 feet. I had been told 200 feet is enough?

I will be flying that plane again today late afternoon. I will then do a range test at 300 feet or more and see how it turns out.

But that little GWS Rx had been flown many times as far away as 1,000 feet, almost a quarter mile, no problems. I don't need to fly much farther than that with my little airplane though a mile would be like having a safety net, but I won't be able to see it.

I'll let you know about today's range test.....

Wan

The GWS can have quite a long range. It is a single conversion receiver and the further away you get, you are more susceptible to hits. Depends on how quite you're flying area is...

PCPhill

200 feet is very good. I have successfully flown with no more than 30' ground range, though it was marginal.

Normally with the model on a table or wall, I get about 100-200ft.

I have paced out the limits I have flown (and crashed) to, so I know hopw far away I was..and surprsingly, even a 48" span model is seldo taken much further than aboyt 250yards. I reckon I have on occasion, gone twice that far with no sign of range loss.

That is on the 60 yard ground test, so I reckon AT LEAST ten times the range wih TX extended as retracted.

Which gives you at least 600 meters in the air. Probably a LOT more.

Yup. hat is not nconsistent with my findings either.

The smallest GWS receivers also have lousy range, but the next size up are good on range. Not so good on rejecting other models especially close in.

Fairly naff oscillators and mixers can easily respond to channels e.g. one half the IF frequency (225 Khz) away. And so on. These effects tend to happen 'close in' rather than at extreme range, as the receiver mixers overload and loads of harmonics get mixed up ...

I tried to work out what a lousy front end would do in the presence of e.g. three or four transmitters all on different frequencies, all getting into the mixer, and basically it's anybody's guess. Suffice to say the more transmitters are on, and the closer in you fly to them, the more chance there is of something unpleasant happening de to specific combinations of them interacting.

The specs on the RX are what I was referring to.

The EASIEST way to check range is REMOVE THE TRANSMITTER ANTENNA and check range. ~Normal~ RC receivers will yield about 40 feet of range when the antenna is stretched out. Saves a bunch of walking.... I do my range checks in my back yard which is 62 feet wide.

David

It's not advisable to remove the transmitter antenna when it is turned on!

Old farts tale.......

David