[hfsig] Fw: Sidebands on Raspberry Pi WSPR carrier - how much does a homebrew 1:1 balun help?

Zoltan Doczi zoltan.doczi at gmail.com
Sat Sep 10 03:44:58 CDT 2016


Excellent job Ron! Thanks so much sharing this!

73,
HA7DCD
Zoltan

2016. szept. 10. de. 1:19 ezt írta ("Ron Ott" <ronott at sbcglobal.net>):

> *Update*:  I wound a second balun with 11.5 turns of #30 insulated wire
> and was more careful about the bifilar windings, starting both the primary
> and secondary at the same point on the Amidon toroid. In addition, I potted
> the wound toroid with common epoxy.  The measured insertion loss decreased
> to 0.55dB at 14.1MHz.  The signal looks great on the WSJT-X waterfall
> display, I don't see any sidebands and I'm not getting double spots now,
> even with a strong signal in the receiver.
>
> Ron, W6XY
>
>
>
> ----- Forwarded Message -----
> *From:* Ron Ott <ronott at sbcglobal.net>
> *To:* TAPR HF Modes SIG Mailing List <hfsig at tapr.org>
> *Sent:* Wednesday, September 7, 2016 7:14 PM
> *Subject:* [hfsig] Sidebands on Raspberry Pi WSPR carrier - how much does
> a homebrew 1:1 balun help?
>
>
> *Construction**:*  I received the parts to make a 1:1 balun this
> afternoon and wound 5 turns each of #30 insulated wire for the primary and
> secondary on an Amidon FT 37-75 toroid core.  The primary and secondary
> windings are bifilar wound (interleaved) around the toroid with leads
> coming from opposite sides of the "O".  The balun is installed in a small
> plastic box with BNC connectors on each end, no potting or glue was used.
>
> *Insertion loss:* I measured 1dB loss at 14MHz when the balun was
> inserted in a coaxial line from my HP signal generator and terminated in
> 50ohms; with some experimentation, this loss could probably be reduced as I
> just guessed at the number of turns based on the AMRAD design for a LF
> balun.  As a result, my ERP will decrease from 18dBm to 17dBm.
>
> *Effect on sidebands due to AC modulation: * Listening to myself on the
> air on 20m while transmitting with the Raspberry Pi, I still get occasional
> double spots due to a sideband 120Hz from the carrier frequency. However,
> the difference betwen the carrier and sideband signal strengths can be over
> 50 dB with the balun, according to WSJT-X, making the RPi WSPR transmitter
> apparently within FCC specs for spurious transmissions.
>
> Looks like this is a worthwhile addition to the RPi TAPR kit setup and
> helps reduce the sidebands 10s of dB, at least at my station.
>
> 73, Ron
>
>
>
>
>
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