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</head><body bgcolor="#FFFFFF" text="#000000">Hi Chris,<br>
<br>
I picked a 7 pole lpf to ensure I met the FCC/Part 97 -43 dBC
requirement. According to Elsie 2.72, the lpf response is -46 dBc for
the second harmonic on 30m. The MOSFET is acting sorta like a switch, so
the output should be primarily odd order harmonics, although the
measurement for 40m shows this isn't completely true :-)<br>
<br>
I'm also assuming that the antenna isn't as good at radiating a second
harmonic compared to the fundamental. I made a 40m dipole model and
analyzed it with 4NEC (I'm new to this process and don't know that I've
necessarily done it correctly). The return loss is -15 dB at 7 MHz and
essentially 0 dB at 14 MHz. I'm assuming that this means for my
particular model the antenna essentially does a 15 dB worse job of
radiating the 40m second harmonic than it does at the fundamental, so
with the existing 30m lpf (-23 dB reduction of second harmonic) the
actual radiation of the second harmonic would be down very roughly -38
dBc (23 + 15). This is still greater than -43 dBc requirement, but we're
dealing with power levels very much less than allowed, so if it's okay
to radiate -43 dBc with 1500 watts, we're allowed to put out 75 mW. The
WSPR transmitter with a 30m lpf is way below that even at 40m.<br>
<br>
Hope this helps.<br>
<br>
73 Bruce<br>
<br>
<br>
<span>KB3CS - Chris wrote on 2/11/2019 5:46 AM:</span><br>
<blockquote type="cite"
cite="mid:CAEHqLs6Dxtat0xNCuCwT=LyNdectFJCnp52-D+ZsBS=Jj2w9VA@mail.gmail.com">
<div dir="ltr">Bryan,<div> with rpitx built and installed from the
repo at <a href="https://github.com/F5OEO/rpitx.git"
moz-do-not-send="true">https://github.com/F5OEO/rpitx.git</a> , you need
only the user files from the WWoT image on your 3B+ (this is the
configuration i have been using). i can make the tar file i made of
the user files available to you, if you need it.</div><div><br></div><div>Bruce,</div><div>
how do the 40m harmonic levels ( -23, -44 dBc ) compare to the 30m
levels? the 40m levels indicate at the very least a 2nd harmonic notch
is needed to conform to the minimum -43 dBc harmonic supression
specification.</div><div><br></div><div> - 3g (base 19) -</div><div><br></div></div>
<br>
<div class="gmail_quote"><div dir="ltr" class="gmail_attr">On Sun, Feb
10, 2019 at 9:35 PM Bruce Raymond <<a
href="mailto:bruce@raymondtech.net" moz-do-not-send="true">bruce@raymondtech.net</a>>
wrote:<br></div><blockquote class="gmail_quote" style="margin:0px 0px
0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex"><div
bgcolor="#FFFFFF">Hi Chris,<br>
<br>
On 40m the second harmonic is -23 dBc and the third harmonic is -44 dBc.
With 200 mW that's about 1 mW for the second harmonic. Not perfect, but
not likely to cause too much interference, especially as the 40m second
harmonic doesn't fall in the 20m WSPR subband.<br>
<br>
<br>
Hi Bryan, <br>
<br>
The problem with WSPR and the Pi 3+ board is incompatible software in
the current build (wiringPi and WsprryPi don't recognize the Pi 3+).
I've put together a new build using Raspbian Stretch instead of Jesse
and the updated versions of wiringPi and WsprryPi and am in the process
of checking it out (been out of town last week ...). We'll put it up on
the TAPR website as an experimental build to try out. I don't have a Pi
3+ to verify it with, so I'm hoping that you'll check it out. I'm still
working on fixing a couple of bugs. I'll keep you apprised of my
progress.<br>
<br>
73 Bruce/ND8I<br>
<br>
<br>
<br>
<br>
<span>KB3CS - Chris wrote on 2/10/2019 7:56 PM:</span><br>
<blockquote type="cite"><div dir="ltr"><div dir="ltr">yes, i know it
will put a signal out on
the airwaves on 40m if you ask it to ... but i'd prefer knowing if the
harmonic emission is too strong to be permissible without getting a
QRPLabs transmit filter first.<div><br></div><div>i started off with a
3B+ with rpitx already installed and tested, so instead of using the
WWoT image, i loop mounted it and made a tar file of the user directory,
then extracted that in a working directory on my Pi. if you're having
boot problems, you may have to carefully check the partition table to
see if you've gotten bitten by the "GB or GiB" problem - not all "32G"
SDCards (for instance) have the same number of bytes in total. for
example, i got a SDCard from Elektor with a Raspbian image on it and it
had an impossible partition table (more blocks defined than the total
number of block available on the device). had to work out how to resize a
filesystem, then write a sensible (and correct) partition table.</div><div><br></div></div> -
\0111 -<div><br><div class="gmail_quote"><div dir="ltr"
class="gmail_attr">On Sun, Feb 10, 2019 at 7:49 PM Bryan Corkran <<a
href="mailto:bcorky@gmail.com" target="_blank" moz-do-not-send="true">bcorky@gmail.com</a>>
wrote:<br></div><blockquote class="gmail_quote" style="margin:0px 0px
0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex">Just
tried it for a while here in VK .<br>
Got spots from nearby states immediately ( 400 to 790 Km )<br>
Would need to to take to our radio club to properly check for birdies.<br>
By the way the 30m Hat and SW wont boot on my Pi 3b + , its fine on my
3b <br>
<br>
Bryan Corkran, VK3KEZ<br>
<br>
> On 11 Feb 2019, at 6:52 am, KB3CS - Chris <<a
href="mailto:kb3cs@arrl.net" target="_blank" moz-do-not-send="true">kb3cs@arrl.net</a>>
wrote:<br>
> <br>
> unlike the 20m HAT, there are no frequency selective elements
before the RF amp.<br>
> <br>
> has anyone tested (or could test) the 30m HAT output when instead a
40m band excitation frequency is used? would the output be to horrible
to inflict on the airwaves?<br>
> <br>
> also, if i'm not mistaken, the latest rpitx release uses GPIO4 for
all output modes.<br>
> <br>
> comments?<br>
> <br>
> - 0x49 - chris KB3CS<br>
> <br>
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