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Date: Mon, 31 Aug 2009 08:53:20 -0400
Message-ID: <57a24ca70908310553w2ce6f632of7320fa67720d2b5@mail.gmail.com>
From: Warren Ziegler <wd2xgj@gmail.com>
To: rsgb_lf_group@blacksheep.org
DomainKey-Status: good (testing) 
Subject: Re: LF: Re: FT-817 at LF/MF
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See also KA7OEI's FT-817 tests:
http://www.ka7oei.com/ft817_rcv.html
--=20
73 Warren K2ORS
                WD2XGJ
                WD2XSH/23
                WE2XEB/2
                WE2XGR/1


On Mon, Aug 31, 2009 at 4:11 AM, Roger Lapthorn<rogerlapthorn@gmail.com>=
 wrote:
> Thanks for these figures Jim. They back up my practical experience.
>
> Yes, on 500kHz the FT817 works surprisingly well with the lash-up untune=
d
> antenna but clearly matching what antenna I have would help further.
>
> On 137 kHz the FT817 RX is unusable and I've been trying with a simple=
 SBL1
> up-converter with some post mixer gain. If I'm going to take a more seri=
ous
> interest in 137/500kHz I'll have to work on the antenna and a better rec=
eive
> system, especially on 137kHz. My real interest is 10m but at the moment=
 the
> LF bands are far more interesting, HI.
>
> Thanks again for this helpful data.
>
> 73s
> Roger G3XBM
>
>
>
> 2009/8/30 James Moritz <james.moritz@btopenworld.com>
>>
>> Dear Roger, LF Group,
>>
>> Re: using the FT-817 and long wire for receiving the WSPR beacons - I=
 have
>> an FT-817 also, which I mostly use with a converter for VLF - MF recept=
ion
>> due to its poor sensitivity at low frequencies. I just did a quick
>> sensitivity check on mine - the following figures are for 10dB SNR usin=
g the
>> 500Hz CW filter:
>>
>> 4.5MHz (the output frequency of my converter):
>> "IPO on" (ie. preamp off) -117dBm
>> "IPO off" (preamp on) -125dBm
>>
>> Sensitivity is much the same over the HF range.
>>
>> 502kHz:
>> IPO on -105dBm
>> IPO off -108dBm
>>
>> 137kHz:
>> IPO on -89dBm
>> IPO off -80dBm
>>
>> So sensitivity is about 20dB down on 500k, which is more or less passab=
le,
>> but a bit disastrous at 137k where it is around 30 - 40dB down dependin=
g on
>> whether the preamp is selected or not.
>>
>> The un-tuned wire will also be a contributing factor - at low frequenci=
es,
>> it will have a high capacitive impedance with a huge mismatch to the lo=
w
>> impedance RX input. You can expect to lose a further 20dB or more at 50=
0k,
>> and 30dB or more at 137k, compared to having some sort of antenna tuner=
.
>>
>> These figures are not unusual =A0for the situation of using a "random"=
 wire
>> with typical amateur HF rigs with general coverage RX, so it is not
>> surprising people often get reasonable results at 500k using this sort=
 of
>> setup for receive, but 137k usually needs a bit more sorting to get use=
ful
>> reception
>>
>> Cheers, Jim Moritz
>> 73 de M0BMU
>>
>>
>>
>>
>
>
>
> --
> -------------------------------------------------------------
> http://g3xbm-qrp.blogspot.com/
> http://www.g3xbm.co.uk
> G3XBM =A0 =A0GQRP 1678 =A0 =A0 =A0ISWL G11088
>