HI Rik and Tony,
It was no problem.
I am simply confusing whether two electrodes (earth )antenna or one
electrode as AC line antenna was experimeted.
7L1RLL Rick
On Thu, 2010-08-12 at 12:09 +0200, Rik Strobbe wrote:
> Tony, Rick,
>
> oops, it seems I responded to the wrong mail.
> My appologies for that, but I got confused by two Ri(c)k's on the reflector.
>
> 73, Rik ON7YD - OR7T
>
> ________________________________________
> Van: [email protected] [[email protected]]
> namens Rik Strobbe [[email protected]]
> Verzonden: donderdag 12 augustus 2010 12:02
> Aan: [email protected]
> Onderwerp: 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
> >>
> >
> >
|
