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Date: Mon, 31 Aug 2009 09:11:54 +0100
Message-ID: <9afca2640908310111g1dd602bete769fd68a7aed6f8@mail.gmail.com>
From: Roger Lapthorn <rogerlapthorn@gmail.com>
To: rsgb_lf_group@blacksheep.org
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Subject: Re: LF: Re: FT-817 at LF/MF
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Thanks for these figures Jim. They back up my practical experience.

Yes, on 500kHz the FT817 works surprisingly well with the lash-up untuned
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 serious
interest in 137/500kHz I'll have to work on the antenna and a better receive
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 reception
> due to its poor sensitivity at low frequencies. I just did a quick
> sensitivity check on mine - the following figures are for 10dB SNR using 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 passable,
> but a bit disastrous at 137k where it is around 30 - 40dB down depending on
> whether the preamp is selected or not.
>
> The un-tuned wire will also be a contributing factor - at low frequencies,
> it will have a high capacitive impedance with a huge mismatch to the low
> impedance RX input. You can expect to lose a further 20dB or more at 500k,
> and 30dB or more at 137k, compared to having some sort of antenna tuner.
>
> These figures are not unusual  for 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 useful
> reception
>
> Cheers, Jim Moritz
> 73 de M0BMU
>
>
>
>
>


-- 
-------------------------------------------------------------
http://g3xbm-qrp.blogspot.com/
http://www.g3xbm.co.uk
G3XBM    GQRP 1678      ISWL G11088

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Thanks for these figures Jim. They back up my practical experience.<br><br=
>Yes, on 500kHz the FT817 works surprisingly well with the lash-up untuned=
 antenna but clearly matching what antenna I have would help further.=A0=
 <br>
<br>On 137 kHz the FT817 RX is unusable and I&#39;ve been trying with a si=
mple SBL1 up-converter with some post mixer gain. If I&#39;m going to take=
 a more serious interest in 137/500kHz I&#39;ll have to work on the antenn=
a and a better receive system, especially on 137kHz. My real interest is=
 10m but at the moment the LF bands are far more interesting, HI. <br>
<br>Thanks again for this helpful data.<br><br>73s<br>Roger G3XBM<br><br><=
br><br><div class=3D"gmail_quote">2009/8/30 James Moritz <span dir=3D"ltr"=
>&lt;<a href=3D"mailto:james.moritz@btopenworld.com">james.moritz@btopenwo=
rld.com</a>&gt;</span><br>
<blockquote class=3D"gmail_quote" style=3D"border-left: 1px solid rgb(204,=
 204, 204); margin: 0pt 0pt 0pt 0.8ex; padding-left: 1ex;">Dear Roger, LF=
 Group,<br>
<br>
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 receptio=
n due to its poor sensitivity at low frequencies. I just did a quick sensi=
tivity check on mine - the following figures are for 10dB SNR using the 50=
0Hz CW filter:<br>

<br>
4.5MHz (the output frequency of my converter):<br>
&quot;IPO on&quot; (ie. preamp off) -117dBm<br>
&quot;IPO off&quot; (preamp on) -125dBm<br>
<br>
Sensitivity is much the same over the HF range.<br>
<br>
502kHz:<br>
IPO on -105dBm<br>
IPO off -108dBm<br>
<br>
137kHz:<br>
IPO on -89dBm<br>
IPO off -80dBm<br>
<br>
So sensitivity is about 20dB down on 500k, which is more or less passable,=
 but a bit disastrous at 137k where it is around 30 - 40dB down depending=
 on whether the preamp is selected or not.<br>
<br>
The un-tuned wire will also be a contributing factor - at low frequencies,=
 it will have a high capacitive impedance with a huge mismatch to the low=
 impedance RX input. You can expect to lose a further 20dB or more at 500k=
, and 30dB or more at 137k, compared to having some sort of antenna tuner.=
<br>

<br>
These figures are not unusual =A0for the situation of using a &quot;random=
&quot; 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 useful reception<br>

<br>
Cheers, Jim Moritz<br>
73 de M0BMU<br>
<br>
<br>
<br>
<br>
</blockquote></div><br><br clear=3D"all"><br>-- <br>----------------------=
---------------------------------------<br><a href=3D"http://g3xbm-qrp.blo=
gspot.com/">http://g3xbm-qrp.blogspot.com/</a><br><a href=3D"http://www.g3=
xbm.co.uk">http://www.g3xbm.co.uk</a><br>
G3XBM =A0 =A0GQRP 1678 =A0 =A0 =A0ISWL G11088<br>

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