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Date: Wed, 10 Oct 2012 15:18:01 +0200
From: =?ISO-8859-15?Q?Stefan_Sch=E4fer?= <Stefan.Schaefer@iup.uni-heidelberg.de>
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Subject: Re: LF: active antenna output termination?
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Hello Hideho,

Thank you for your ideas.

Yes, i'm using isolation transformers where ever i can.

The problem is nearly solved, at least i can now receive reasonably on=20
MF and LF to the same time. However i could make some improvements on=20
the LF RX design. It is all homemade and i learned a lot since that time =
:-)

73, Stefan/DK7FC


Am 10.10.2012 15:06, schrieb Hideho YAMAMURA:
> Hello Stefan,
>
> Did you try feeding with battery ?
> Also, an isolating-transformer between the power-feeder and RX ?
>
> I experienced 1-2dB drop of noise level with the battery,
> and small improvement with the transformer.
> (no IM experience though)
>
> Perhaps these may help you further finding the cause of your problem.
>
> 73s,
>
> Hideho YAMAMURA, JF1DMQ
>
>
>
> Stefan Sch=E4fer wrote:
>> Thank you Claudio,
>>
>> I will consider that when the probe is down from the roof next. There=20
>> are a few dB in reserve, i'm still far away from the RX noise.
>> But now it looks much better! Still some IM but only a little. Taking=20
>> into account that AFN is arround, that's a positive result.
>> If there would be oscillations on the output of the probe, then i=20
>> would see them across the 50 Ohm resistor in the shack, at full=20
>> amplitude, right?
>>
>> 73, Stefan/DK7FC
>>
>>
>> Am 09.10.2012 15:26, schrieb Claudio Pozzi:
>>
>>>
>>> The emitter follower transistor have a very low output impedance, no=20
>>> problems
>>> for receiving purpose but...   if you use a long coaxial cable you=20
>>> connect a
>>> capacitance of about 100 pF/meter between output and ground. The=20
>>> circuit can
>>> become unstable and oscillate, I found that a 27 or 33 ohm resistor=20
>>> in series
>>> to the output help to kill the oscillation and the signal loss is a=20
>>> little
>>> less than 6 dB (voltage, 3dB power).
>>>
>>> I's a good practice to put a few ohm resistor in series at the low=20
>>> impedance
>>> output devices (OP-AMP, emitter follower, 74HCxxx buffers etc)=20
>>> driving a
>>> capacitive load to prevent oscillation.
>>>
>>> 73
>>>
>>> Claudio, ik2pii
>>>
>>
>>
>>
>
>
>