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A short video of sBitx working
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Very nice, and some fascinating capabilities.
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I¡¯m hoping I have enough time while teaching part-time high school this semester to delve into some of this code! Gordon KX4Z On Jul 31, 2022, at 10:30, Ashhar Farhan <farhanbox@...> wrote: |
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John, You must have seen that the video has a jump at 8:25. I switched to FT8 at that point, tuned around for about 2 minutes but 21 MHz was surprisingly quiet. I had to snip out that uninteresting part. I will get one recorded today. Usually 21MHz is bustling with FT8 activity during the day. - f On Mon, Aug 1, 2022, 4:11 AM John AE5X <ae5x@...> wrote: Thanks for the video. Any chance of one showing the FT8 functionality in action? |
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Don't see any reason it would not receive ok down there.
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though you may need to hack the RPi software some. The stock sBitx is not appropriate for transmitting on 630 meters. There is no transmit low pass filter appropriate for 630 meters, you would have to add one or you would generate some very strong harmonics. Jerry, KE7ER On Tue, Aug 2, 2022 at 02:32 PM, Alan Cooper wrote:
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The spec sheet is on? You could transmit on 630 khz. I am not sure if the PA transformer inductance will be enough that low.? The exciter will work right down to 10 KHz or so. On Wed, Aug 3, 2022, 3:02 AM Alan Cooper <cqw7aln@...> wrote:
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I understand the need for a low pass filter. That is needed for the IC 7300 also which I built a low pass filter for it which was easy enough. It produces real nice harmonic spurs right through the AM? broadcast band without one, and gives a normal watt meter fits because one cannot tell where the rf is getting produced is in the electromagnetic spectrum. It also causes an swr meter on the radio to read incorrectly since the reflected spurs power causes the rf foldback to activate and cut the transmit power way down. the rf tranformer in the sBitx has me wondering... is the what would pass for an output matching network in the PA, that is being refered to ? thanks Alan On Tue, Aug 2, 2022, 6:09 PM Ashhar Farhan <farhanbox@...> wrote:
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Yes, the transformer at T8 matches the extremely low impedance coming out of the IRFZ24N's
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to something near 50 ohms.? There is also a discussion here about an external antenna matcher to match that 50 ohms from the sBitx into whatever impedance the antenna presents.? The sBitx transmitter is designed to work from 30mhz to 3mhz, a factor of 10 to 1. Very tough to get transformers to work well across such a wide frequency range. Since T8 has to operate at 40 Watts, that is the most critical with regard to operating at 0.474mhz. Operating at 0.474mhz would best be done by increasing the windings on all transformers that must work at the operating frequency, namely T2, T5, T7 and T8. Jerry, KE7ER On Wed, Aug 3, 2022 at 03:04 AM, Alan Cooper wrote:
I understand the need for a low pass filter. That is needed for the IC 7300 also which I built a low pass filter for it which was easy enough. It produces real nice harmonic spurs right through the AM? broadcast band without one, and gives a normal watt meter fits because one cannot tell where the rf is getting produced is in the electromagnetic spectrum. It also causes an swr meter on the radio to read incorrectly since the reflected spurs power causes the rf foldback to activate and cut the transmit power way down. |
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There's an excellent wikipedia article about this transmitter:??https://en.wikipedia.org/wiki/Grimeton_Radio_Station
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"The Grimeton transmitter is the last surviving example of an Alexanderson alternator, the only radio station left from the pre-vacuum tube era, and is still in working condition. Each year, on a day called?, either on the last Sunday in June, or on the first Sunday in July, whichever comes closer to 2 July, the site holds an open house during which the transmitter is started up and transmits test messages on 17.2?kHz using its??SAQ, which can be received all over Europe." The good news is that you have almost an entire year to prepare for the next transmission. Jerry, KE7ER On Wed, Aug 3, 2022 at 06:05 AM, Niels Jalling wrote:
If the receiver goes down to 10kHz you can try to catch the sendings from the Grimeton transmitter at 17.2 kHz. |
Aaron K5ATG
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