Hi Rik I have seen the data on the length effect you quote and it is stated
in the QST reprint of Harold's original article from the 1930s. (well worth
a read if you can find it)
I am wondering whether this is due to the effect of a less that optimum
ground condition. I see not reason why there should be an optimum length for
a travelling wave antenna. If the height and ground permitivity are correct
then the longer the better(??). Most amateur Beverages are probably sited
over "too good" a ground and probably not at an optimised height. I cant
really believe that attenuation would lead to this effect.
Even without the velocity factor effect I believe there could be a mechanism
similar to a waveguide directional coupler, which would produce a good
signal. I also throw into discussions about terminated loops (often to be
told I am wrong !!)
Interesting antennas from the real beginning of radio (or wireless, as we
call it :-)) )
Alan
----- Original Message -----
From: "Rik Strobbe" <[email protected]>
To: <[email protected]>
Sent: Thursday, August 12, 2010 11:02 AM
Subject: RE: LF: Earth antenna
Tony,
my remarks were not meant as critisism, just as a "warning" that the
measured values should be interpreted with caution.
About beverages:
Typical length is 1 to 2 lambda, it seems that directivity is optimal at
these lenghts.
Short beverages (<< 1 lambda) loose directivity (and directivity is the main
reason beverages are used).
Most beverages are terminated at the far end to make the pattern
unidirectional, but this is no must (leaving out the termination will get
you a bidirectional pattern).
So at first sight the 2 main difference between a earth antenna and beverage
is:
- beverage is >= lambda, earth antenna <<< lambda
- beverage is terminated to ground at the far end (resistor to ground),
earth antenna is just connected to ground at the far end
73, Rik ON7YD - OR7T
________________________________________
Van: [email protected] [[email protected]]
namens Tony [[email protected]]
Verzonden: donderdag 12 augustus 2010 11:30
Aan: [email protected]
Onderwerp: Re: LF: Earth antenna
Hi Rik.
I take your point, but I did say that it was "non-technical"
The earth was the main station earth which is a short (1.5m) length of
22mm copper pipe to an earth mat and radials and was the same earth used
for both antennas.
The receiver was AC powered but there was no trace of a signal at all
between connecting the different antenna wires
But a question for the techs, when does a long "earth" antenna become a
Beverage antenna ?
Or, how short can a Beverage antenna be before it ceases to be any
practical use ?
73, Tony, EI8JK
On 12/08/2010 01:34, Rick Wakatori wrote:
> Hello Tony,
> Show us your RX earth terminal side and whether AC voltage supply or
> DC battery did you use for the experiment. AC line can be a good long
> antenna for receiving.
> 7L1RLL Rick
>
> On Wed, 2010-08-11 at 16:16 +0200, Rik Strobbe wrote:
>> Hello Tony,
>>
>> measuring voltages on untuned antennas is "tricky", in particular with
>> small electrical antennas (compared to the wavelength) as these tend
>> to have large reactive components.
>> On 60kHz the L-antenna you described has a reactive component of about
>> 10000 Ohm while the resistive part will be some 10's to some 100's Ohm
>> (mostly loss resistance). So properly tuning the antenna will increase
>> the RX voltage by several S-points.
>> Ground loop antennas on the other hand seem more broadband.
>> Maybe that explains why they perform better at lower frequencies
>> ( compared to the untuned L-antenna).
>>
>> Anyway, your L-antenna should perform well on 500kHz.
>>
>> 73, Rik ON7YD
>>
>>
>> ______________________________________________________________________
>> Van: [email protected]
>> [[email protected]] namens Tony [[email protected]]
>> Verzonden: woensdag 11 augustus 2010 14:05
>> Aan: [email protected]
>> Onderwerp: Re: LF: Earth antenna
>>
>>
>>
>> Hi Roger.
>>
>> The soil here is well drained peaty topsoil about 400mm - 500mm deep
>> on a mixture of slate and shale and although I am 500m from the sea, I
>> am 75m above the water.
>> I have no idea what the electrical conductivity is but I imagine it's
>> probably lower in the winter when my windows get a covering of salt
>> during storms. It would be interesting to pick on one reliable ground
>> wave transmission and monitor it through various weather conditions.
>> It would also be interesting to see how it works lower in frequency
>> (sub 50 KHz), which is something that I will definitely look into.
>>
>> 73,
>> Tony, EI8JK
>>
>>
>> On 11/08/2010 11:32, Roger Lapthorn wrote:
>>> Thanks for this Tony.
>>>
>>> Do you know what sort of soil/rock you have beneath you there? Here
>>> I am on relatively low conductivity chalk/clunch with clay a few
>>> miles to the north west under fenland peat.
>>>
>>> If the earth electrode antenna is behaving as a loop (a debated
>>> theory) then it is most effective is the "loop in the ground" is as
>>> large as possible, which would be the case with low conductivity
>>> soil/rocks underneath: the return path between electrodes would be
>>> forced to take a longer route deeper into the ground. If the soil
>>> between the electrodes has good conductivity then the return current
>>> would flow directly making the effective loop size small.
>>>
>>> In the last few days we've had a lot of rain here and the results on
>>> 500kHz last night with the earth electrode antenna suggest the rain
>>> made little difference to performance with reception several times
>>> by PA0A. This is counter-intuitive to me, as I would have expected
>>> levels to be weaker if the soil was wet (loop formed being smaller
>>> etc.). Of course it could have been that the contact resistance of
>>> the earth probes was lower and overall the two effects cancelled?
>>>
>>> Whatever the theory says, the earth electrode "antenna" has some
>>> mileage especially when, like me, there is little space for large
>>> "in the air" antennas. Sure, a big vertical or large loop in the air
>>> would be better (I think), but this is about experimenting and
>>> discovering the limits of possibilities.
>>>
>>> Good luck and keep everyone posted if you do further tests.
>>>
>>> 73s
>>> Roger G3XBM
>>>
>>>
>>>
>>> On 11 August 2010 10:34, Tony<[email protected]> wrote:
>>> I have finally found the time to get some (radio) work done
>>> here and got my 2nd tower finished and I erected an inverted
>>> L, 10m vertical and 30m top rising to 15m at the far end. I
>>> still have the "earth antenna" which is just a length of
>>> wire laying on the ground 80m long and terminated directly
>>> to an earth stake and laying roughly in the same direction
>>> as the top wire of the L .
>>> Comparing the two gave some very interesting results.
>>>
>>> 10 MHz CW L = S7 earth = S1
>>> 7 MHz CW L = S9 earth = S3
>>> R. Bristol 1566 KHz L = 0 earth = S2
>>> Donebach 153 KHz L = S6 earth = S8
>>> DCF77 77.5 KHz L = S3 earth = S5
>>> MSF 60 KHz L = S4 earth = S8
>>>
>>> All very non-technical I know, neither antenna was matched
>>> or tuned in any way and was all done about 13:00z.
>>> There was no noticeable difference in the noise level but
>>> when I tried it before the earth antenna was very much
>>> quieter after dark. I will try and repeat this tonight and
>>> see what the difference is then.
>>>
>>> Tony, EI8JK.
>>>
>>>
>>>
>>>
>>> --
>>> http://g3xbm-qrp.blogspot.com/
>>> http://www.g3xbm.co.uk
>>> http://www.youtube.com/user/g3xbm
>>> G3XBM GQRP 1678 ISWL G11088
>>
>
>
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