Hi Mark, Yes I am interpreting it the other way, ie the "spurious emissions attenuated by ... the lessor of (23,70) == 23dBc for very low power signals.
However it's a bit confusing and you (and Glen) might be right ..... I will seek clarification from ACMA. It may also be different in other parts if the world. -/- Also in response to Glen's earlier email - much of the slow fall off of the spectrum on the blog post (http://www.rowetel.com/images/rpitx/rpitx_spectrum_10kbps.png) is due it being unfiltered FSK (i.e. not really about the Pi). In busier bands, the bandwidth could be reduced by using a lower bit rate. Today we were testing in on 2M at 1000 bit/s and below, and we could hardly hear or see the carrier on a SDR (let alone the spurious). In higher bands, there tends to be more space available, so less of a problem. Cheers, David On 10/8/20 5:07 pm, Mark Jessop wrote: > I think David is going purely by the spurious emissions limits from the > Amateur LCD: > image.png > > So for 10mW TX power, 43+10log(0.01) = 23 dB. > HOWEVER, it's also worth looking at how the above legislation is > interpreted. > When we talk about spurious emissions, we usually talk in dB relative to > the carrier of the wanted signal (dBc). So the result of the above > calculation should really be expressed as -23 dBc, with the other limit > being -50 dBc. > The letter of those two is -50 dBc. Is this how it should be > interpreted? I don't know. > > How appropriate are these limits when attempting to play nicely with > other users of the amateur bands is another issue. > I certainly wouldn't want to be amplifying the output of a RPi TX > without doing something to seriously clean it up, if that's even possible. > > 73 > Mark VK5QI > > On Mon, Aug 10, 2020 at 3:47 PM glen english <g...@cortexrf.com.au > <mailto:g...@cortexrf.com.au>> wrote: > > David, looking at that link and plots you sent, that radio will not > meet > community and other band user spectral purity expectations. > > At UHF, It needs to be better than -70dBc in an SSB Bandwidth immediate > adjacent > > At 1MHz away, -110dBc in an SSB BW... > > and proportionally better at lower frequencies.... > > -40dBc in band you will make alot of other radio amateurs unhappy... > > Here is a worked example from your 144.5 plot. > > +10dBm - 40 = -30dBc in SSB BW > > Now, how about an SSB users 10km away line of site (-95dB), say 0dBi to > 0dBi, > > you put -30 - 95 = -125dBm noise in his receiver, an effect desense of > about 18dB. > > and that is only with +10dBm TX power. > > g > > > On 10/08/2020 7:52 am, David Rowe wrote: > > With the addition of a LPF I believe it meets the spectral purity > > requirements of the Amateur LCD on 2M: > > > > http://www.rowetel.com/?p=7207 > > > > and on HF: > > > > http://www.rowetel.com/?p=6317 > > > > - David > > > > On 10/8/20 6:50 am, glen english wrote: > >> except that the Pi transmitter has unacceptable spectral purity. > >> > >> On 9/08/2020 7:18 pm, Adrian Musceac wrote: > >>> Thanks David for the news. > >>> One question: how high can the Pi transmitter go in frequency? > >>> Our 70 cm band is pretty crowded, but the 23 cm band and > 2305-2400 MHz > >>> bands are underutilized and we want to make use of them. The Pi/RTL > >>> system is a good candidate because of price. > >>> > >>> Adrian > >> > >> _______________________________________________ > >> Freetel-codec2 mailing list > >> Freetel-codec2@lists.sourceforge.net > <mailto:Freetel-codec2@lists.sourceforge.net> > >> https://lists.sourceforge.net/lists/listinfo/freetel-codec2 > > > > _______________________________________________ > > Freetel-codec2 mailing list > > Freetel-codec2@lists.sourceforge.net > <mailto:Freetel-codec2@lists.sourceforge.net> > > https://lists.sourceforge.net/lists/listinfo/freetel-codec2 > > -- > Glen English > RF Communications and Electronics Engineer > > CORTEX RF > & > Pacific Media Technologies Pty Ltd > > ABN 40 075 532 008 > > PO Box 5231 Lyneham ACT 2602, Australia. > au mobile : +61 (0)418 975077 > > > > > _______________________________________________ > Freetel-codec2 mailing list > Freetel-codec2@lists.sourceforge.net > <mailto:Freetel-codec2@lists.sourceforge.net> > https://lists.sourceforge.net/lists/listinfo/freetel-codec2 > > > > _______________________________________________ > Freetel-codec2 mailing list > Freetel-codec2@lists.sourceforge.net > https://lists.sourceforge.net/lists/listinfo/freetel-codec2 > _______________________________________________ Freetel-codec2 mailing list Freetel-codec2@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/freetel-codec2
