I recently spent the night in my van camped in a woodland glade and
decided to try out an idea i had been thinking about for shortwave
broadcast reception.
The receiver was an Eddystone EC10 which I recently restored, it has a 'floating' aerial input circuit of nominally 50 ohms. I connected the 'earth' socket to the receiver casing and the 'aerial' socket to a
length of wire in the conventional way.
Instead of hanging up the wire, I laid it along the ground under the
van, so it had greater capacitive coupling to the ground than it did to
the van. The receiver was on the wooden 'kitchen worktop' in the van,
so it had greater capacitance coupling to the van than to the ground
outside. This meant that, in effect, one terminal of the aerial input circuit was connected to ground and the other was connected to the van -
so the van was acting as the aerial.
The results above 5 Mc/s were quite acceptable, with excellent reception
from medium-to-strong stations and hardly any interference. Below 5
Mc/s, where the capacitive coupling was ineffective, the bands were
almost silent.
If I had used an earthing stake and electrically joined the receiver
earth to the van body, I might have had even better results.
Liz Tuddenham <liz@poppyrecords.invalid.invalid> wrote:
I recently spent the night in my van camped in a woodland glade and
decided to try out an idea i had been thinking about for shortwave broadcast reception.
The receiver was an Eddystone EC10 which I recently restored, it has a 'floating' aerial input circuit of nominally 50 ohms. I connected the 'earth' socket to the receiver casing and the 'aerial' socket to a
length of wire in the conventional way.
Instead of hanging up the wire, I laid it along the ground under the
van, so it had greater capacitive coupling to the ground than it did to
the van. The receiver was on the wooden 'kitchen worktop' in the van,
so it had greater capacitance coupling to the van than to the ground outside. This meant that, in effect, one terminal of the aerial input circuit was connected to ground and the other was connected to the van -
so the van was acting as the aerial.
The results above 5 Mc/s were quite acceptable, with excellent reception from medium-to-strong stations and hardly any interference. Below 5
Mc/s, where the capacitive coupling was ineffective, the bands were
almost silent.
If I had used an earthing stake and electrically joined the receiver
earth to the van body, I might have had even better results.
Did you detect any cats?
I recently spent the night in my van camped in a woodland glade and
decided to try out an idea i had been thinking about for shortwave
broadcast reception.
The receiver was an Eddystone EC10 which I recently restored, it has a >'floating' aerial input circuit of nominally 50 ohms. I connected the >'earth' socket to the receiver casing and the 'aerial' socket to a
length of wire in the conventional way.
Instead of hanging up the wire, I laid it along the ground under the
van, so it had greater capacitive coupling to the ground than it did to
the van. The receiver was on the wooden 'kitchen worktop' in the van,
so it had greater capacitance coupling to the van than to the ground
outside. This meant that, in effect, one terminal of the aerial input >circuit was connected to ground and the other was connected to the van -
so the van was acting as the aerial.
The results above 5 Mc/s were quite acceptable, with excellent reception
from medium-to-strong stations and hardly any interference. Below 5
Mc/s, where the capacitive coupling was ineffective, the bands were
almost silent.
If I had used an earthing stake and electrically joined the receiver
earth to the van body, I might have had even better results.
On 17/07/2025 05:21, john larkin wrote:
What's the capacitance of a van to ground?
What's the relative humidity at the time of measurement?
What's the capacitance of a van to ground?
Jeff Layman <Jeff@invalid.invalid> wrote:
On 17/07/2025 05:21, john larkin wrote:
What's the capacitance of a van to ground?
What's the relative humidity at the time of measurement?
No idea and no way of telling. The site is 60 miles away and it has
rained since.
The van is approximately 4.8 metres x 1.8 metres and has a ground
clearance of 30 cm - so the 'capacitor' has a plate area of 8.46 sq m
and a spacing of 0.30 m. If we assume the ground to be a perfect
conductor and air to have a dielectric constant of 1, this gives a >capacitance of 255 pF.
The capacitance between van and ground will shunt the signal; for best >results at lower frequencies it is the capacitance between the wire and >ground that needs to be maximised.
On Thu, 17 Jul 2025 08:47:50 +0100, liz@poppyrecords.invalid.invalid
(Liz Tuddenham) wrote:
Jeff Layman <Jeff@invalid.invalid> wrote:
On 17/07/2025 05:21, john larkin wrote:
What's the capacitance of a van to ground?
What's the relative humidity at the time of measurement?
No idea and no way of telling. The site is 60 miles away and it has
rained since.
The van is approximately 4.8 metres x 1.8 metres and has a ground
clearance of 30 cm - so the 'capacitor' has a plate area of 8.46 sq m
and a spacing of 0.30 m. If we assume the ground to be a perfect
conductor and air to have a dielectric constant of 1, this gives a >capacitance of 255 pF.
The capacitance between van and ground will shunt the signal; for best >results at lower frequencies it is the capacitance between the wire and >ground that needs to be maximised.
The van will shield the wire, especially with dry soil. So drape the
wire away from the van, not under it.
Better yet would be a ground rod.
The van capacitance can be tuned away.
On 17/07/2025 05:21, john larkin wrote:
What's the capacitance of a van to ground?
What's the relative humidity at the time of measurement?
On Thu, 17 Jul 2025 08:21:31 +0100, Jeff Layman <Jeff@invalid.invalid>
wrote:
On 17/07/2025 05:21, john larkin wrote:
What's the capacitance of a van to ground?
What's the relative humidity at the time of measurement?
Do you think that matters?
Am 16.07.25 um 11:18 schrieb Liz Tuddenham:
I recently spent the night in my van camped in a woodland glade and
decided to try out an idea i had been thinking about for shortwave
broadcast reception.
HB9CVQ has made a lot of measurements on that, and also
HFSS simulations IIRC.
See for example:
<Â Â Â Â https://www.youtube.com/watch?v=2J_wSaWFUNAÂ Â Â Â Â >
73, Gerhard DK4XP
I recently spent the night in my van camped in a woodland glade and
decided to try out an idea i had been thinking about for shortwave
broadcast reception.
On 17/07/2025 17:30, john larkin wrote:
On Thu, 17 Jul 2025 08:47:50 +0100, liz@poppyrecords.invalid.invalidIf the wire is acting as a ground, then it should not matter whether
(Liz Tuddenham) wrote:
Jeff Layman <Jeff@invalid.invalid> wrote:
On 17/07/2025 05:21, john larkin wrote:
What's the capacitance of a van to ground?
What's the relative humidity at the time of measurement?
No idea and no way of telling. The site is 60 miles away and it has
rained since.
The van is approximately 4.8 metres x 1.8 metres and has a ground
clearance of 30 cm - so the 'capacitor' has a plate area of 8.46 sq m
and a spacing of 0.30 m. If we assume the ground to be a perfect
conductor and air to have a dielectric constant of 1, this gives a
capacitance of 255 pF.
The capacitance between van and ground will shunt the signal; for best
results at lower frequencies it is the capacitance between the wire and
ground that needs to be maximised.
The van will shield the wire, especially with dry soil. So drape the
wire away from the van, not under it.
Better yet would be a ground rod.
The van capacitance can be tuned away.
it is under or along side the van. Using the whole van as an antenna
seems like a good idea. It should be very wideband.
John
On 17/07/2025 17:27, john larkin wrote:
On Thu, 17 Jul 2025 08:21:31 +0100, Jeff Layman <Jeff@invalid.invalid>
wrote:
On 17/07/2025 05:21, john larkin wrote:
What's the capacitance of a van to ground?
What's the relative humidity at the time of measurement?
Do you think that matters?
Perhaps not. As noted at ><https://en.wikipedia.org/wiki/Relative_permittivity#Environment>, "The >relative permittivity of air changes with temperature, humidity, and >barometric pressure". According to the ref (25) quoted, it's
"1.4×10^?6/%RH".
I thought it would have been a lot higher. Although pure water is a good >insulator, moisture in the air will have dissolved various gases which
would increase conductivity, such as carbon dioxide and nitrogen oxides.
I have no idea how much of an effect they would have, if any.
john larkin <jl@glen--canyon.com> wrote:
On Thu, 17 Jul 2025 08:47:50 +0100, liz@poppyrecords.invalid.invalid
(Liz Tuddenham) wrote:
Jeff Layman <Jeff@invalid.invalid> wrote:
On 17/07/2025 05:21, john larkin wrote:
What's the capacitance of a van to ground?
What's the relative humidity at the time of measurement?
No idea and no way of telling. The site is 60 miles away and it has
rained since.
The van is approximately 4.8 metres x 1.8 metres and has a ground
clearance of 30 cm - so the 'capacitor' has a plate area of 8.46 sq m
and a spacing of 0.30 m. If we assume the ground to be a perfect
conductor and air to have a dielectric constant of 1, this gives a
capacitance of 255 pF.
The capacitance between van and ground will shunt the signal; for best
results at lower frequencies it is the capacitance between the wire and
ground that needs to be maximised.
The van will shield the wire, especially with dry soil. So drape the
wire away from the van, not under it.
Better yet would be a ground rod.
The van capacitance can be tuned away.
I think you have misunderstood what I was doing, I was using the van as
an aerial and the aerial wire as an earth. Because I didn't have a
ground rod handy, I just laid the wire on the ground and relied on its >capacitance to earth - above 5Mc/s that seemed to work.
It just happened that the receiver was inside the van - i.e. inside its
own aerial, but that didn't matter because it was only responding to the >difference in potential between two input terminals and didn't care what
each one was connected to.
On Thu, 17 Jul 2025 17:38:22 +0100, John R Walliker
<jrwalliker@gmail.com> wrote:
On 17/07/2025 17:30, john larkin wrote:
On Thu, 17 Jul 2025 08:47:50 +0100, liz@poppyrecords.invalid.invalidIf the wire is acting as a ground, then it should not matter whether
(Liz Tuddenham) wrote:
Jeff Layman <Jeff@invalid.invalid> wrote:
On 17/07/2025 05:21, john larkin wrote:
What's the capacitance of a van to ground?
What's the relative humidity at the time of measurement?
No idea and no way of telling. The site is 60 miles away and it has
rained since.
The van is approximately 4.8 metres x 1.8 metres and has a ground
clearance of 30 cm - so the 'capacitor' has a plate area of 8.46 sq m
and a spacing of 0.30 m. If we assume the ground to be a perfect
conductor and air to have a dielectric constant of 1, this gives a
capacitance of 255 pF.
The capacitance between van and ground will shunt the signal; for best >>> results at lower frequencies it is the capacitance between the wire and >>> ground that needs to be maximised.
The van will shield the wire, especially with dry soil. So drape the
wire away from the van, not under it.
Better yet would be a ground rod.
The van capacitance can be tuned away.
it is under or along side the van. Using the whole van as an antenna
seems like a good idea. It should be very wideband.
John
The wire has capacitance to the van and capacitance to the earth. The wire-van capacitance reduces the signal level and increases the wire's impedance as the effective antenna.
Things will get worse in sand or dry soil.
john larkin <jl@glen--canyon.com> wrote:
On Thu, 17 Jul 2025 17:38:22 +0100, John R Walliker
<jrwalliker@gmail.com> wrote:
On 17/07/2025 17:30, john larkin wrote:
On Thu, 17 Jul 2025 08:47:50 +0100, liz@poppyrecords.invalid.invalidIf the wire is acting as a ground, then it should not matter whether
(Liz Tuddenham) wrote:
Jeff Layman <Jeff@invalid.invalid> wrote:
On 17/07/2025 05:21, john larkin wrote:
What's the capacitance of a van to ground?
What's the relative humidity at the time of measurement?
No idea and no way of telling. The site is 60 miles away and it has
rained since.
The van is approximately 4.8 metres x 1.8 metres and has a ground
clearance of 30 cm - so the 'capacitor' has a plate area of 8.46 sq m
and a spacing of 0.30 m. If we assume the ground to be a perfect
conductor and air to have a dielectric constant of 1, this gives a
capacitance of 255 pF.
The capacitance between van and ground will shunt the signal; for best >> >>> results at lower frequencies it is the capacitance between the wire and >> >>> ground that needs to be maximised.
The van will shield the wire, especially with dry soil. So drape the
wire away from the van, not under it.
Better yet would be a ground rod.
The van capacitance can be tuned away.
it is under or along side the van. Using the whole van as an antenna
seems like a good idea. It should be very wideband.
John
The wire has capacitance to the van and capacitance to the earth. The
wire-van capacitance reduces the signal level and increases the wire's
impedance as the effective antenna.
The distance between the conductor and the underside of the van floor
was 30 cms, the distance between the conductor and the soil was the
thickness of the PVC insulation - less than a millimetre. The ratio of >capacitances to the wire was overwhelmingly 'earthy'.
Things will get worse in sand or dry soil.
Yes, but this was a clearing at the bottom of a wooded hillside with
mulch for the floor. It had dried out a bit but, even in the height of >Summer, there is still condensation from dew in the early morning, so
nothing in a forest is ever truly dry.
There was a sort of fad once, in Popular Electronics, for surface-sheet-resistance commmunications. One used an audio amp and a
couple of ground rods as the transmitter and another pair of rods and
an amp as the receiver. A sort of substitute for ham radio.
Dipole fields fall off fast so range was short.
| Sysop: | Keyop |
|---|---|
| Location: | Huddersfield, West Yorkshire, UK |
| Users: | 546 |
| Nodes: | 16 (0 / 16) |
| Uptime: | 164:26:11 |
| Calls: | 10,385 |
| Calls today: | 2 |
| Files: | 14,057 |
| Messages: | 6,416,518 |