To: rsgb_lf_group@blacksheep.org
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 <5A81C025.13685.51C8EA38@mike.dennison.ntlworld.com>
 <212280367.20180212164700@gmail.com>
 <F239BC15-3E1C-4501-A76B-A43E6452E8CF@gmail.com>
From: N1BUG <paul@n1bug.com>
Message-ID: <db0b1454-3d79-4978-ace5-016c9b82a123@n1bug.com>
Date: Mon, 12 Feb 2018 12:23:54 -0500
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Subject: Re: LF: Do I need an attenuator on LF RX??
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DCF39 and HGA22 are clearly evident of course, but I note there is 
something on 133 kHz that comes up in sync with those two. It's not 
DCF49 which is lower, around 129 kHz. I suspect either the receiver 
is overloaded, not enough front end filtering yet, or a combination 
of the two. It may be more of challenge to get the filtering tight 
enough in Europe where you have the strong signals from DCF49, 
HGA22, DFC39 and some very strong broadcast stations not much higher 
in frequency...

Regarding the noise "hump" in or around the 137 kHz band, could this 
be just the resonance of the transmitting antenna? I use a separate 
receiving antenna which is nearby (about 15 meters from the 
transmitting vertical). When the transmitting antenna is resonated 
on 137 kHz I see a very pronounced noise "hump" over a 2 to 3 kHz 
range. When the transmitting antenna is not resonated for LF, I do 
not see that and the noise floor is fairly constant over several 
tens of kHz (the passband of the front end filter).

73,
Paul


On 02/12/2018 12:08 PM, John Rabson wrote:
> Possibly DCF39 and its companion? I believe they are used to control some sort of electricity grid.
> 
> John F5VLF
> 
>> On 12 Feb 2018, at 17:47, Chris Wilson <dead.fets@gmail.com> wrote:
>>
>>
>>
>> Hello Mike, I just listened to what looks like the AM modulated bursts
>> around 139 and 135.5 kHz and they sound like bursts of data, nothing
>> intelligible whatsoever.
>>
>> Monday, February 12, 2018, 4:26:13 PM, you wrote:
>>
>>> Chris,
>>
>>> It looks like you have a broadcast station where it shouldn't be (at
>>> 132.65kHz) and several other spurious stations in that area, so you
>>> may well have unwanted signals within the 136kHz band, especially at
>>> night (your recording seems to have been done during the middle of
>>> the day). You might improve things by by-passing the pre-amp. It
>>> would do no harm just by experimenting with an attenuator but why
>>> attenuate and amplify at the same time unless the preamp also
>>> provides another function such as matching? It seems the only
>>> front-end selectivity on that receiver is a narrow bandpass so you
>>> would really benefit from some additional wider filtering, eg an LPF
>>> with a cut-off just below the LW BC band.
>>
>>> Mike, G3XDV
>>
>>
>>
>>
>>
>> -- 
>> Best regards,
>> Chris                            mailto:dead.fets@gmail.com
>>
>>
> 
> 
> 

-- 
Paul
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