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Author Topic: Stubby aerials  (Read 2923 times)

roycv

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Stubby aerials
« on: January 07, 2007, 05:20:01 pm »

Hi all, I bought a Fleet 40 Mhz RC set, 4 ch., with a stubby aerial.  This was in 1998 and I thought it would be a safety feature with the aerial being a foot long and flexible.

It took me quite a while to work out that  the stubby aerial had a range of about 50 feet at most.

 I bought a standard aerial, fitted it  and restored the usual expected range, out of sight, well its my glasses really!

Does anyone have a good experience with any other than the standard length aerials?

regards to all Roy
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BobF

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Re: Stubby aerials
« Reply #1 on: January 07, 2007, 07:05:21 pm »

Hi Roy,

I have a fellow club member who has one from the same era, and he has no problem with range.

Is the receiver aerial vertical or horizontal? I know a lot of modellers that route the aerial under the deck, but in my experience this is not good practice. Several of them have had problems with range including me, that went as soon as the aerial was vertical. Not suggesting that this is the problem in your case, but it is worth noting. Also unless the transmitter aerial is of the correct design length, this can cause problems and failure of output components. As with C B radios where the aerial was a separate item, a SWR meter had to be used to tune the aerial.

Hope some of the above may be of use to you.

Bob
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Doc

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Re: Stubby aerials
« Reply #2 on: January 07, 2007, 07:17:09 pm »

Roy,
You've opened a real 'can of worms' - lol, are you ready for this?
There are several 'standard' lengths for antennas, depending on who is defining the 'standards', which/what group or industry, and the specific use of the antenna/aerial.  A receiving antenna is one of those 'the longer the better' thingys  until you get to some ridiculous length (for the proposed place of use).  Receivers just aren't that particular as to what an antenna 'tastes' like, they get extremely 'hungry' so more-is-better.  Transmitters are different in that they have certain requirements in antenna/aerials.  Has to 'taste' just right!  If it doesn't 'taste' right, not much power is actually transmitted (a 'picky' eater!).  But!  The radio industry can change the 'taste' of things very easily, so shorter antennas can be used/eaten.  The problem is that while the antenna 'tastes' right, it isn't quite as 'filling' as the 'real thing'.  Meaning that the usable range for any shortened antenna/aerial is changed, that change being that it just doesn't go as far (sort of like Chinese food, you get hungry again very quickly).
If that isn't the most far fetched analogy you've ever heard, you need to quit hanging around 'those' kind'a people!
The simple fact is that 'shortened' antennas just won't have the same 'range' as 'full sized' antennas because of changes in their radiation pattern.  There's no direct, simple relation between range and 'shortness', it's complicated, and depends on each individual situation.  The 'standard' for the R/C industry isn't the same as for a 'communications' industry.  The maximum usable ranges for the two types are vastly different , as in do you really want a signal that can be 'heard' in another country?  I don't!
There.  If that doesn't have you completely confused, then I really am a genius!  Fat chance...
 - 'Doc
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roycv

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Re: Stubby aerials
« Reply #3 on: January 08, 2007, 10:45:05 pm »

Hi all thanks for your response.
Doc, hi,  I was an air radar fitter in the RAF some years ago now, and am conversant with aerial theory.  So when a manufacturer offers a stubby aerial I expect him to do his homework first.  I would expect there was compensation for the short physical aerial, centre winding or whatever to give an electrically correct length aerial.

I recall a comment from the owner of Fleet who said they were not as good as he had hoped!  I still have the aerial but I doubt whether I will use it again.  The actual equipment is excellent and in regular use.

BobF hi, I have 3 rx's as the Tx has a 8 model memory I switch between them. (currently in 2 boats with one going spare at the moment)
I agree with you about rx ae. position and my boats all have a fixed aerial usually up the mast and I have small gold plated plugs and sockets. These were component parts of 76 way computer cable connectors, retained from when I was a computer engineer.

The rx. aerial is cut down to a few inches and a gold plated connector is soldered on, this mates up with the connector of the fixed aerial in the boat and brings it back to the correct length.

I am interested though that you know someone who uses one.  I would be interested in knowing just how much range he does get.

Regards to all Roy

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Mankster

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Re: Stubby aerials
« Reply #4 on: January 08, 2007, 11:03:43 pm »

I have a 'stubby' aerial on my Robbe TX as well as the full lenght telescopic one. Range is down by about 40% but still fine for most of my purposes, and it is great for use indoors (geeting around doorways, boat in one hand in the radio in another, and less likely to poke your self in the eye). It is a helical aerial though, so max rang in achieved by pointing the aerial at the model rather than perpendicular to the model with the telescopic one to get the best range.

BobF

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Re: Stubby aerials
« Reply #5 on: January 09, 2007, 03:15:25 pm »

Hi Roy,

I will be seeing Ted on the 20th of this month.  I will try and remember to get as much detail as I can from him, as to exact model of transmitter etc. and also the length of his receiver aerial as well. Although the pond he sails on would be just about the limit you mentioned, he goes to open days around the country, and I have never heard him complain of being low on range. He sails it at Wilton park on their open day, and that is quite a large pond/lake?

I use the 2mm gold bullet connectors for my aerials. I never worry too much about the length, as long as it is no shorter than the original. On my One Meter yachts, I just clip it to the base of the mast. So that means on a calm day with little wind and No1 sails fitted, it is the original length plus 72 vertical inches. I can sail approx 90 meeter's with the transmitter aerial down before I run out of pond !!!!!!!!!!!!!!! (only done as a range check)

Bob
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Doc

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Re: Stubby aerials
« Reply #6 on: January 10, 2007, 04:20:04 am »

Mankster,
Helically wound antennas can be directional, but not at the commonly used R/C frequencies.  At 40 Mhz they behave as they do at HF frequencies, merely shorten the antenna, they are not directional.  Pointing the antenna at the boat does not help, as a matter of fact, it will shorten range.  There's typically a 'null' off the 'pointy' ends of antennas, less radiated signal than off the 'sides'.
If pointing the antenna at your boat does seem to help, I'd guess that your receive antenna is more horizontal than vertical (polarized).  An antenna that is helically would is only directional if the transmitted signal is a 'circular polarization'.  The dimensions of a circularly polarized antenna are based on wave length, and at 40 Mhz, would be very uncomfortable to lug around, as in very large.
Another little 'gem' is that most helically would antennas are very inefficient, lossy.
 - 'Doc
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BobF

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Re: Stubby aerials
« Reply #7 on: March 23, 2007, 03:24:43 pm »

Hi roycv,
Finally spoke to Ted regarding range problems.

He has never had a range problem with his RC equipment.
I did not get the model number, but it is from the 2000 era. The last of the batch before the company changed hands previously. Hope this is of some help.

Bob
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roycv

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Re: Stubby aerials
« Reply #8 on: March 29, 2007, 06:13:15 pm »

Hi Bobf thanks for your response, perhaps there is a fault in the aerial I have.
regards Roy
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