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From: Roger Lapthorn <rogerlapthorn@gmail.com>
Date: Thu, 25 Jan 2018 20:48:11 +0000
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To: "rsgb_lf_group@blacksheep.org" <rsgb_lf_group@blacksheep.org>
Subject: Re: LF: Re: 136kHz WSPR experiment
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Thanks Mike. I seem to remember that I got surprisingly good results with
my EFP (schematic shown a few days ago) feeding into the FT817 on 136kHz,
This has not be tried since before my 2013 stroke. If I am correct the EFP
is in a drawer somewhere! I shall have to try to find it. I have a lot of
junk.

Next season I shall try the EFP on 136kHz RX.

BTW, I find sensitivity on 136kHz with the FT817 is better with IPO
selected. Maybe this relates to your findings?

73s
Roger G3XBM

On 25 January 2018 at 20:31, Michael Sapp <wa3tts@verizon.net> wrote:

> Roger: I tried to post a reply to the group prior but it did apparently
> did not make it past the admin monitor or it exceeded message size limit.
>
> I found the key to getting the FT-817 to receive well on LF and MF is to
> use a low pass filter with good in-band return loss characteristics between
> the antenna (e-probe, EWE, etc.) and the
> FT-817.  If you have ever tried listening to an AM broadcast station with
> the FT-817 and it's VHF rubber duck antenna, you know it is stone-cold deaf
> that way.  But if you use an antenna with a reasonable 50 ohm match at
> lower HF, the FT-817 hears AM band stations (530 ~ 1600 kHz) very well. The
> same principle applies to LF/MF in the 100kHz to 500 kHz range.  The FT-817
> receiver front end needs to see something close to 50 ohms to receive
> signals efficiently.  But it also needs most of the AM band energy rejected
> so it will not overload.  Using an LPF with a good pass band match seems to
> solve the problem when using an e-probe antenna at LF/MF with the FT-817.
> Also do not use the preamp in the FT-817. Turn off the AGC and NB.
>
> There is a VE7BPO NDB filter with build information online that is easy to
> construct with commonly available parts if you do not have an LF/MF LPF
> filter available. I'm sure if you try it or another good LF/MF LPF with
> your FT-817 you will see an immediate order-of-magnitude improvement in
> receive performance at LF/MF.  I use a variation of the VE7BPO filter for
> 630m and a 9th order 300 kHz Butterworth LPF for LF.  The Butterworth LPFs
> have very good pass-band return loss and the FT-817 responds very well to
> having the filter between the antenna and the radio at LF.
>
> For even better performance I run a broadband LF/MF 2N3904 preamp after my
> LPF and either a 3dB pad or a 50 ohm universal diplexer for the frequency
> of interest after the preamp and into the FT-817.  I built the 2N3904
> preamp last night to try it out based on your recent FT-817 LF postings...
>
> Last night I was able to decode WH2XXP in AZ from PA with the FT-817 at
> some 3000 km distant 55 times with the FT-817 on the 2200m band. I was just
> able to occasionally decode WH2XXP with only the LPF and no post filter
> preamp.  With the 2N3904 preamp into a 3 dB pad and then into the FT-817 I
> was able to obtain a best overnight SNR of -18 on WH2XXP at 3000 km
> distant. I did need to use the attenuator in the FT-817 to adjust the rx
> level.
>
> Quick sketch of preamp and FT-817 rx layout...
>
> https://www.dropbox.com/s/tmszk33xuyjjtnc/2N3904P.JPG?dl=0
>
> Pix of filter-preamp setup but with 137 kHz diplexer on preamp  output
> instead of 3 dB pad...
>
> https://www.dropbox.com/s/tms4gruu2x8azz4/flpredp.jpg?dl=0
>
> 73 Mike wa3tts
>

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<div dir=3D"ltr"><div>Thanks Mike. I seem to remember that I got surprising=
ly good results with my EFP (schematic shown a few days ago) feeding into t=
he FT817 on 136kHz, This has not be tried since before my 2013 stroke. If I=
 am correct the EFP is in a drawer somewhere! I shall have to try to find i=
t. I have a lot of junk.</div><div><br></div><div>Next season I shall try t=
he EFP on 136kHz RX.</div><div><br></div><div>BTW, I find sensitivity on 13=
6kHz with the FT817 is better with IPO selected. Maybe this relates to your=
 findings?</div><div><br></div><div>73s</div><div>Roger G3XBM</div></div><d=
iv class=3D"gmail_extra"><br><div class=3D"gmail_quote">On 25 January 2018 =
at 20:31, Michael Sapp <span dir=3D"ltr">&lt;<a href=3D"mailto:wa3tts@veriz=
on.net" target=3D"_blank">wa3tts@verizon.net</a>&gt;</span> wrote:<br><bloc=
kquote class=3D"gmail_quote" style=3D"margin:0 0 0 .8ex;border-left:1px #cc=
c solid;padding-left:1ex">
<div dir=3D"ltr">
<div dir=3D"ltr">
<div style=3D"FONT-SIZE:12pt;FONT-FAMILY:&#39;Calibri&#39;;COLOR:#000000">
<div>Roger: I tried to post a reply to the group prior but it did apparentl=
y did=20
not make it past the admin monitor or it exceeded message size limit.</div>
<div>=C2=A0</div>
<div>I found the key to getting the FT-817 to receive well on LF and MF is =
to=20
use a low pass filter with good in-band return loss characteristics between=
 the=20
antenna (e-probe, EWE, etc.) and the </div>
<div>FT-817.=C2=A0 If you have ever tried listening to an AM broadcast stat=
ion=20
with the FT-817 and it&#39;s VHF rubber duck antenna, you know it is stone-=
cold deaf=20
that way.=C2=A0 But if you use an antenna with a reasonable 50 ohm match at=
=20
lower HF, the FT-817 hears AM band stations (530 ~ 1600 kHz) very well. The=
 same=20
principle applies to LF/MF in the 100kHz to 500 kHz range.=C2=A0 The FT-817=
=20
receiver front end needs to see something close to 50 ohms to receive signa=
ls=20
efficiently.=C2=A0 But it also needs most of the AM band energy rejected so=
 it=20
will not overload.=C2=A0 Using an LPF with a good pass band match seems to =
solve=20
the problem when using an e-probe antenna at LF/MF with the FT-817.=C2=A0 A=
lso=20
do not use the preamp in the FT-817. Turn off the AGC and NB.</div>
<div>=C2=A0</div>
<div>There is a VE7BPO NDB filter with build information online that is eas=
y to=20
construct with commonly available parts if you do not have an LF/MF LPF fil=
ter=20
available. I&#39;m sure if you try it or another good LF/MF LPF with your F=
T-817 you=20
will see an immediate order-of-magnitude improvement in receive performance=
 at=20
LF/MF.=C2=A0 I use a variation of the VE7BPO filter for 630m and a 9th orde=
r 300=20
kHz Butterworth LPF for LF.=C2=A0 The Butterworth LPFs have very good pass-=
band=20
return loss and the FT-817 responds very well to having the filter between =
the=20
antenna and the radio at LF.</div>
<div>=C2=A0</div>
<div>For even better performance I run a broadband LF/MF 2N3904 preamp afte=
r my=20
LPF and either a 3dB pad or a 50 ohm universal diplexer for the frequency o=
f=20
interest after the preamp and into the FT-817.=C2=A0 I built the 2N3904 pre=
amp=20
last night to try it out based on your recent FT-817 LF postings...</div>
<div>=C2=A0</div>
<div>Last night I was able to decode WH2XXP in AZ from PA with the FT-817 a=
t=20
some 3000 km distant 55 times with the FT-817 on the 2200m band. I was just=
 able=20
to occasionally decode WH2XXP with only the LPF and no post filter preamp.=
=C2=A0=20
With the 2N3904 preamp into a 3 dB pad and then into the FT-817 I was able =
to=20
obtain a best overnight SNR of -18 on WH2XXP at 3000 km distant. I did need=
 to=20
use the attenuator in the FT-817 to adjust the rx level.</div>
<div>=C2=A0</div>
<div>Quick sketch of preamp and FT-817 rx layout...</div>
<div>=C2=A0</div>
<div><a title=3D"https://www.dropbox.com/s/tmszk33xuyjjtnc/2N3904P.JPG?dl=
=3D0" href=3D"https://www.dropbox.com/s/tmszk33xuyjjtnc/2N3904P.JPG?dl=3D0"=
 target=3D"_blank">https://www.dropbox.com/s/<wbr>tmszk33xuyjjtnc/2N3904P.J=
PG?<wbr>dl=3D0</a></div>
<div>=C2=A0</div>
<div>Pix of filter-preamp setup but with 137 kHz diplexer on preamp=C2=A0 o=
utput=20
instead of 3 dB pad...</div>
<div>=C2=A0</div>
<div><a title=3D"https://www.dropbox.com/s/tms4gruu2x8azz4/flpredp.jpg?dl=
=3D0" href=3D"https://www.dropbox.com/s/tms4gruu2x8azz4/flpredp.jpg?dl=3D0"=
 target=3D"_blank">https://www.dropbox.com/s/<wbr>tms4gruu2x8azz4/flpredp.j=
pg?<wbr>dl=3D0</a></div>
<div>=C2=A0</div>
<div>73 Mike wa3tts</div></div></div></div>
</blockquote></div><br></div>

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