From: "Mike Dennison" <mike.dennison@ntlworld.com>
To: rsgb_lf_group@blacksheep.org
Date: Mon, 23 Jul 2012 15:18:52 +0100
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In-reply-to: <20120723152524.350920d89ielpuck@w3mail.netikka.fi>
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Subject: Re: LF: Receive interference at MF
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I do not use a transformer, and this may well help at MF. 

I only transmit on 136kHz (where noise is not a problem) and have 
tried a transformer to improve the match. However, although the match 
is slightly better, any advantage is consumed by losses (heat) in the 
transformer (my Tx has 800W output). 

When I start to transmit on 472kHz next year, I expect to need a 
matching transformer. The transmitter power will be lower, so heat 
dissipation will be less of a problem. 

In the next few days, I will try a transformer just on receive and 
report back.

Mike, G3XDV
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D

> Mike, do you use a transformer between the feeder coax and the
> antenna?
> 
> A transformer can serve double purpose as impedance trasformer to 
> match the resonated antenna to 50ohm and at the same time galvanically
>  isolate the antenna from the coax. This requires separate primary and
>  secondary windings on the transformer and the coax shield must not be
>  earthed at the antenna end.
> 
> The above arrangement is perhaps a substitute for insulated radials 
> and can easily be reverted to unisolated by connecting the coax shield
>  to the antenna ground.
> 
> At my QTH the isolating transformer helps with interference but the 
> Mini-Whip still has an edge over that solution. However, when the 
> resonant antenna is operational it degrades the mini-whip SNR around 
> the resonant frequency due to coupling as the distance between the 
> antennas is less than 10 metres. Can't have it all at the same time 
> 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=E4fer
> >> <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
> >> >>
> >>
> >
> >
> >
> >
> >
> 
>