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Re: uBITX tuning issue
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Dave Bottom
Jeff, If you are certain of your wiring, then you should check that all grounds are connected (to the same point). See the construction notes about a heavy gauge ground wire from Power Connector to a common ground point that the PCB Ground Plane is connected to.? Although the ground lead to the Encoder is connected on the PCB ground plane you can have strange behavior if you have long leads, or the PCB Ground Plane is not connected with a heavy gauge wire to theh Power connector (solder lug under a nut for one of stand-offs).?? Mine is in a metal box and I have twisted all the encoder leads prior to connecting, and as noted in the instructions, keep these as short as is reasonable for your layout.? You will note that Farhan has done this in his assembly pictures. This is a surprisingly quiet radio.? First generation Amateur gear (e.g Drake Solid State Rigs with Digital Readouts e.g. TR7) had far more birdies and weird noise behavior from their digital display board (shielded better in their later design rigs e.g. TR5). Careful layout, proper ground planes on the PCB, and surface mount parts that make each stage very tidy must help a lot with the MicroBITX.? I'm liking it a lot, if you can't tell. Construction Practices I'm actually going to replace all of the leads to jacks with shielded cables as I have them all on the rear panel (now the leads are twisted together and run against the metal case under the PCB) and the shields and Power Ground (plus PCB Ground Plane) should all connect to one Ground lug against the metal case.? In other words don't connect each to a different ground points (ground loops can result).? You can use an xacto nife tip to release the pin contact and re-solder leads that you want to shield where they had been crimped.? Just use a very small amount of solder (thin solder and a small tip soldering iron), then reinsert. These are necessary construction practices to ensure stable operating radios, especially when you begin transmitting. Any pickup on the wrong leads can give strange results.? In my case (pun intended) all Raduino ground contacts are connected to the front panel and all audio grounds are connected at the rear panel.? The Mic Audio ground is entirely separate on purpose to eliminate RFI and audio ground loops.? ?The only lead that comes from the Raduino connector to the Mic jack is PTT.? This could be run outside of shielded Mic leads and tie wrapped to the shielded Mic cable.? In most modern HF radios (last 25 years) the Mic shield connects to the chassis at the Mic connector for RFI shielding, but both Mic leads (Mic+ and Mic-) pass through separate pins of the Mic connector (usually an 8-Pin Foster style Mic connector) and the Mic- lead does reach ground until it is at the Mic pre-amp on whatever PCB it resides (usually the TX/IF PCB).? That's where the Mic is terminated.? In this way there are few chances for RFI or Audio Ground Loop issues.?? New SDRs that have a DAC (Digital Analog Converter)? that supports both TX and RX audio, then all leads now go to the same PCB ground plane area at the DAC.? It's a lot simpler, but both Mic leads are quasi balanced (off ground at the connector). Dave WI6R On Sat, Jan 6, 2018 at 1:51 PM, jlco001 via Groups.Io <jlco001@...> wrote: Hello all, --
73 Dave WI6R |
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