Hi Stefan,
>+6 dB, so now you're getting twice the antenna current with
>the same power?
No,only about 10% more (calculated) as the VSWR is a bit better.
R went from ~60 Ohm to 50 Ohm,reactance being cancelled out.
The increase in signal strength by 6dB comes from reduced ground losses due
to vertical polarization as opposed to horizontal polarization in dipole mode.
>Can you show us the image showing your house and the antenna again? I
Attached once more for convenience (see also link at the end).
Red traces = dipole legs (2x155m)
Yellow trace = open wire feeder (42m)
>remember there was a coax of some 10m between TX and dipole feed point
That must be someone different. -:)
Here the feeder runs directly into the shack,vertical part about 6m.
So in T-Antenna mode there's quite a bit of top load...
Let's see how I can manage the earth problem.
I believe for reception I will further stay with the dipole mode because it's
extremely
quiet ( -110dBm or true ~S3 in 200Hz BW) due to careful balancing and its remote
location from the houses.
When receiving I can afford up to 10-15dB signal loss on MW without
degrading SNR.
http://no.nonsense.ee/qthmap/?qth=JN68KJ79WJ
73
Clemens
DL4RAJ
>-----Original Message-----
>From: [email protected]
>[mailto:[email protected]] On Behalf Of Stefan Schäfer
>Sent: Sunday, January 19, 2014 10:14 PM
>To: [email protected]
>Subject: Re: LF: MW Antenna [was:RE: Clemens on MF!!]
>
>Hello Clemens,
>
>What did i say...
>So now you need a clean earth and maybe you can use a relay while
>transmitting. The relay switches both earths parallel and during RXing
>you just use the clean earth.
>+6 dB, so now you're getting twice the antenna current with
>the same power?
>Can you show us the image showing your house and the antenna again? I
>remember there was a coax of some 10m between TX and dipole feed point
>(?). If you can install an earth system directly below the feed point,
>then the RF current cannot cause TVI at home.
>
>73, Stefan/DK7FC
>
>
>Am 19.01.2014 16:11, schrieb Clemens Paul:
>> Hi Wolf,
>>
>> I've tried the T-Antenna mode this weekend.
>> It was excited against PE (protective earth of the house).
>> Matching was surprisingly easy by a series C of around 1340pF,
>> R (the real part) happened to be 50 Ohm (in dipole mode it
>varies between 60 and 70 Ohm).
>> The effect was dramatic in any sense.
>> Ground wave signal strength went up by ~ 20dB as measured on
>a remote Perseus in
>> Amberg (nr Nürnberg) this afternoon.
>> Sky wave signal strength during last night went up by at
>least 6dB,maybe 10dB
>> (diifficult to measure because of qsb while changing the
>configuration) in DL as well
>> in OH (1900km distance) on a remote Perseus.
>> Now the downside:Rx noise level went up by roughly the same
>amount (day/night)
>> and funny things happened when TXing with full power.
>> The TV and some lights in the living room went off and
>on,there was hum in the telephone
>> etc.
>> The RX noise problem could easily be solved by switching the
>two antenna modes
>> automatically with the PTT line and a few relays.
>> The EMI problem perhaps by a separate earth?
>>
>> 73
>> Clemens
>> DL4RAJ
>>
>>
>>
>>> -----Original Message-----
>>> From: [email protected]
>>> [mailto:[email protected]] On Behalf Of wolf_dl4yhf
>>> Sent: Saturday, January 11, 2014 11:32 PM
>>> To: [email protected]
>>> Subject: Re: LF: RE: Clemens on MF!!
>>>
>>> Hi Clemens,
>>>
>>>
>>> Am 11.01.2014 22:58, schrieb Clemens Paul:
>>>
>>>> The dipole is a horizontal 90°V, 8-15m high and according to
>>>>
>>> EZNEC it has a spheroidal
>>>
>>>> pattern with no nulls.
>>>>
>>> Ok... that makes a difference.
>>>
>>>> The vertical part of the feeder is only about 6m long.
>>>>
>>> So the rainworms will be cosy and warm around the lower parts of the
>>> antenna, hi..
>>>
>>>> Tomorrow I'll check the impedance of the antenna aagainst
>>>>
>>> ground with both feeder wires
>>>
>>>> connected
>>>> and see if I can match it to 50 Ohm,dependent on the
>available parts.
>>>>
>>> That would be a good indicator for the ground conductivity.
>>> At the local antenna farm, the total resistance (after
>>> compensating the
>>> reactive part with a series coil) went up from 26 to approx 35 ohms
>>> within a few months.
>>> During transmit, I simply use the PE (plus possibly the underground
>>> cables) as counterpoise. During RX, the PE is disconnected from the
>>> antenna's own 'ground' which consists of a few buried wires,
>>> to prevent
>>> QRM from the mains creeping in. Another remote RX antenna is already
>>> planned, most likely it will be a small active loop or a system of
>>> crossed loops.
>>>
>>> Cheers,
>>> Wolf.
>>>
>>> ( where is everyone .. now hearing only " -... .. .- " ? )
>>>
>>>
>>>
>>
>>
>
Dipol 2x156m.JPG
Description: JPEG image
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