[hfsig] soliciting advice regarding 30m HAT

Mon Feb 11 08:51:40 EST 2019

Hi Chris,

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 :-)

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.

Hope this helps.

73 Bruce

KB3CS - Chris wrote on 2/11/2019 5:46 AM:
> Bryan,
>   with rpitx built and installed from the repo at 
> https://github.com/F5OEO/rpitx.git , 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.
>
> Bruce,
> 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.
>
>  - 3g (base 19) -
>
>
> On Sun, Feb 10, 2019 at 9:35 PM Bruce Raymond <bruce at raymondtech.net 
> <mailto:bruce at raymondtech.net>> wrote:
>
>     Hi Chris,
>
>     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.
>
>
>     Hi Bryan,
>
>     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.
>
>     73 Bruce/ND8I
>
>
>
>
>     KB3CS - Chris wrote on 2/10/2019 7:56 PM:
>>     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.
>>
>>     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.
>>
>>      - \0111 -
>>
>>     On Sun, Feb 10, 2019 at 7:49 PM Bryan Corkran <bcorky at gmail.com
>>     <mailto:bcorky at gmail.com>> wrote:
>>
>>         Just tried it for a while here in VK .
>>         Got spots from nearby states immediately ( 400 to 790 Km )
>>         Would need to to take to our radio club to properly check for
>>         birdies.
>>         By the way the 30m Hat and SW wont boot on my  Pi 3b + , its
>>         fine on my  3b
>>
>>         Bryan Corkran, VK3KEZ
>>
>>         > On 11 Feb 2019, at 6:52 am, KB3CS - Chris <kb3cs at arrl.net
>>         <mailto:kb3cs at arrl.net>> wrote:
>>         >
>>         > unlike the 20m HAT, there are no frequency selective
>>         elements before the RF amp.
>>         >
>>         > 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?
>>         >
>>         > also, if i'm not mistaken, the latest rpitx release uses
>>         GPIO4 for all output modes.
>>         >
>>         > comments?
>>         >
>>         >  - 0x49 -  chris  KB3CS
>>         >
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