Message-ID: <2B993CD1387E48D689FB9EF68B409ABB@Mike2PC>
From: "Michael Sapp" <wa3tts@verizon.net>
To: <rsgb_lf_group@blacksheep.org>
References: <CAHAQVWMs_556+qzyTJWOqDmgrPGzX62J2FfBH3ceRZ3fbfTfDg@mail.gmail.com> <001a01d394ff$8f3f54a0$adbdfde0$@go2.pl> <CAHAQVWPYMZEHGzQ0aQX_rPKUUkDLuLk3T=x6WmqjA5uckCsGuQ@mail.gmail.com> <00c801d3960f$4ce1ab10$e6a50130$@go2.pl> <CAHAQVWMMKM2ZoyyKty6v97K00RNeSxmpk6KmdePx0Nod4UYJcw@mail.gmail.com>
In-Reply-To: <CAHAQVWMMKM2ZoyyKty6v97K00RNeSxmpk6KmdePx0Nod4UYJcw@mail.gmail.com>
Date: Thu, 25 Jan 2018 15:31:19 -0500
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Subject: LF: Re: 136kHz WSPR experiment
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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=20
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=3D0

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=3D0

73 Mike wa3tts
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<HTML><HEAD></HEAD>
<BODY dir=3Dltr>
<DIV dir=3Dltr>
<DIV style=3D"FONT-SIZE: 12pt; FONT-FAMILY: 'Calibri'; COLOR: #000000">
<DIV>Roger: I tried to post a reply to the group prior but it did =
apparently did=20
not make it past the admin monitor or it exceeded message size =
limit.</DIV>
<DIV>&nbsp;</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.&nbsp; If you have ever tried listening to an AM broadcast =
station=20
with the FT-817 and it's VHF rubber duck antenna, you know it is =
stone-cold deaf=20
that way.&nbsp; 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.&nbsp; The =
FT-817=20
receiver front end needs to see something close to 50 ohms to receive =
signals=20
efficiently.&nbsp; But it also needs most of the AM band energy rejected =
so it=20
will not overload.&nbsp; 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.&nbsp; Also=20
do not use the preamp in the FT-817. Turn off the AGC and NB.</DIV>
<DIV>&nbsp;</DIV>
<DIV>There is a VE7BPO NDB filter with build information online that is =
easy to=20
construct with commonly available parts if you do not have an LF/MF LPF =
filter=20
available. I'm sure if you try it or another good LF/MF LPF with your =
FT-817 you=20
will see an immediate order-of-magnitude improvement in receive =
performance at=20
LF/MF.&nbsp; I use a variation of the VE7BPO filter for 630m and a 9th =
order 300=20
kHz Butterworth LPF for LF.&nbsp; 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>&nbsp;</DIV>
<DIV>For even better performance I run a broadband LF/MF 2N3904 preamp =
after my=20
LPF and either a 3dB pad or a 50 ohm universal diplexer for the =
frequency of=20
interest after the preamp and into the FT-817.&nbsp; I built the 2N3904 =
preamp=20
last night to try it out based on your recent FT-817 LF =
postings...</DIV>
<DIV>&nbsp;</DIV>
<DIV>Last night I was able to decode WH2XXP in AZ from PA with the =
FT-817 at=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.&nbsp;=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>&nbsp;</DIV>
<DIV>Quick sketch of preamp and FT-817 rx layout...</DIV>
<DIV>&nbsp;</DIV>
<DIV><A =
title=3Dhttps://www.dropbox.com/s/tmszk33xuyjjtnc/2N3904P.JPG?dl=3D0=20
href=3D"https://www.dropbox.com/s/tmszk33xuyjjtnc/2N3904P.JPG?dl=3D0">htt=
ps://www.dropbox.com/s/tmszk33xuyjjtnc/2N3904P.JPG?dl=3D0</A></DIV>
<DIV>&nbsp;</DIV>
<DIV>Pix of filter-preamp setup but with 137 kHz diplexer on =
preamp&nbsp; output=20
instead of 3 dB pad...</DIV>
<DIV>&nbsp;</DIV>
<DIV><A =
title=3Dhttps://www.dropbox.com/s/tms4gruu2x8azz4/flpredp.jpg?dl=3D0=20
href=3D"https://www.dropbox.com/s/tms4gruu2x8azz4/flpredp.jpg?dl=3D0">htt=
ps://www.dropbox.com/s/tms4gruu2x8azz4/flpredp.jpg?dl=3D0</A></DIV>
<DIV>&nbsp;</DIV>
<DIV>73 Mike wa3tts</DIV></DIV></DIV></BODY></HTML>

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