Message-ID: <20120723152524.350920d89ielpuck@w3mail.netikka.fi>
Date: Mon, 23 Jul 2012 15:25:24 +0300
From: phl@netikka.fi
To: rsgb_lf_group@blacksheep.org
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 <43A1879A-58FF-480A-A148-65811EAB486E@dk8kw.de>
 <500D215D.27455.45EBAE5@mike.dennison.ntlworld.com>
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Subject: Re: LF: Receive interference at MF
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Hello Mike, Geri, LF

Mike, do you use a transformer between the feeder coax and the antenna?

A transformer can serve double purpose as impedance trasformer to =20
match the resonated antenna to 50ohm and at the same time galvanically =20
isolate the antenna from the coax. This requires separate primary and =20
secondary windings on the transformer and the coax shield must not be =20
earthed at the antenna end.

The above arrangement is perhaps a substitute for insulated radials =20
and can easily be reverted to unisolated by connecting the coax shield =20
to the antenna ground.

At my QTH the isolating transformer helps with interference but the =20
Mini-Whip still has an edge over that solution. However, when the =20
resonant antenna is operational it degrades the mini-whip SNR around =20
the resonant frequency due to coupling as the distance between the =20
antennas is less than 10 metres. Can't have it all at the same time =20
unless a "remote-detune" function is provided for the resonant antenna.

BR

Paul-Henrik, OH1LSQ


Quoting Mike Dennison <mike.dennison@ntlworld.com>:

> Geri,
>
> Have you looked at your ground system? On 136kHz a network of earth
> stakes works well as a receive ground. However, I have found that at
> MF (including topband) I need insulated radials to reduce the
> interference from household electronics, particularly my own plasma
> TV. On 500kHz, the best results involve disconnecting one (but not
> all) of my earth stakes, and on topband I disconnect all of the
> stakes. My garden is only 20m long but I still get receive
> improvements with radials.
>
> Mike, G3XDV
> =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D
>
>> Yes, it's partly due to groundwave/skywave conditions but I am already
>> known as the crocodile (big mouth, tiny ears) over here in Northern
>> Germany because my signal is 599 all around while I can barely hear
>> people. On LF I had optimized my receiving system pretty much but on
>> MF I have a high noise floor, probably from household electronics. One
>> solution surely is to put an e-field antenna some 25m away from the
>> house into the garden, equally far away from all houses in the
>> neighborhood. Currently I am using my transmitting umbrella antenna to
>> receive, which always proved best on LF but probably needs some
>> re-thinking for MF. Additionally I got hold of a R&S EK070 on EBay
>> last week and I am eagerly waiting for it to arrive. At least then
>> nobody can complain that my receiver is lousy ;)
>>
>> Lots of things to do and to explore on MF, which is a great part of
>> the fun. And until I am fully set up for TX and RX on 475 kHz I use
>> some non-amateur communication devices such as Echolink and VHF
>> repeaters to do my day-to-day communications ;)
>>
>> Best 73
>>
>> Geri, DK8KW & DI2BO
>>
>>
>> On 22.07.2012, at 19:18, Stefan Sch=C3=A4fer
>> <Stefan.Schaefer@iup.uni-heidelberg.de> wrote:
>>
>> > Geri,
>> >
>> > I bet it is only due to groundwave limitations. Normally you should
>> > hear Mal. So far he is the strongest signal i heared on MF. But at
>> > 11 UTC you can forget about MF skywave, at least in central Germany
>> > and in summer.
>> >
>> > Last night DF0WD and DF6NM were perfectly audible. But this is after
>> > 0 AM local! Later even the QSB was lower and the signals stronger.
>> >
>> > 73, Stefan/DK7FC
>> >
>> >
>> > Am 22.07.2012 12:24, schrieb Holger 'Geri', DK8KW - DI2BO - W1KW:
>> >>
>> >> Mal,
>> >>
>> >> Sorry, no coppy here, however, I know that my rx-equipment needs
>> >> improvemen. EK 070 and Mini Whip is already on order ...
>> >>
>> >> 73
>> >>
>> >> Geri, DK8KW & DI2BO
>> >>
>> >> ----- Original Message -----
>> >> From: mal hamilton
>> >> To: rsgb
>> >> Sent: Sunday, July 22, 2012 12:13 PM
>> >> Subject: LF: 502 CQ
>> >>
>> >> MF
>> >> Now CQ  around 502 on CW
>> >>
>> >> De mal/g3kev
>> >>
>>
>
>
>
>
>