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Shielded /Coax connectors for wiring in BitX40smd
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I'm getting by without coax, using the wiring harnesses provided, but I did cut them reasonably short. ? On critical signals I twisted the signal wire with the associated ground wire, perhaps 1 or 2 turns per inch. ?Caps (signal to ground) on both ends of the tuning pot cable are a good idea. ?My antenna cable is about 2" long, I wouldn't want to go much longer without using coax. ?If you use coax, I'd ground the braid on both ends in all cases, the center conductor carries the signal. ?Something like RG178 coax is small and flexible enough. ?Should be able to extract pins from the connectors provided by pressing the springy metal tab at the wire end of the the rectangular window while gently tugging at the wire. ?Then you can solder RG178 directly to those connector pins. I think a conservatively designed commercial rig might use coax for all of the signals below to avoid potential trouble. ?I'm listing them roughly in the order in which I'd consider them critical, opinions will vary. ? ? ? Main board DDS connector to Raduino ? ? Main board to tuning pot middle pin (and 0.1uF caps on both ends) ? ? Main board to antenna connector ? ? Main board to microphone ? ? Main board to volume control center pin ? ? Main board to volume control top pin ? ?? ? ?? On Sat, May 13, 2017 at 01:01 pm, Thomas Noel wrote:
Where are the places that most benefit from shielded connectors linking components? ? |
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Thomas Noel
开云体育Jerry,Thanks for the ordered list of recommended coax connections. Just what this Dr ordered! You recommended grounding the shield at both ends of each coax link. I’ve seen others recommend only grounding one end. Is this one of those “which brand of oil is the best for my motorcycle” questions, or is there good science behind one answer or the other? Thomas W Noel KF7RSF
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I recently joined the group and I just ordered a BITX40/Raduino so I am trying to come up to speed. ?I am wondering if it is necessary/desirable to? put the Raduino VFO into it's own shielded box or at least make some attempt to shield it from the main board to avoid any unwanted interactions (birdies etc) ? Cheers Michael VE3WMB? |
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This business of not connecting the ground braid on one end of a piece of coax came up in regard to tuning clicks from the Raduino. ?Some here felt that since multiple grounds from Bitx40 to Raduino created "ground loops", this could be a reason for the clicks. ?But the consensus here seems to be that the clicks are adequately suppressed by using the correct Si5351 library and with proper power supply filtering on the Raduino. ?I don't recall anybody reporting that they solved their tuning clicks by disconnecting the signal ground associated with the DDS signal. ?But you are welcome to try it, unlike motorcycle oil you don't need to wait 100000 miles to test this particular hypothesis. ? From post 25386: ?There are two causes for the clicks: ?power supply to the raduino, and new firmware. ?The firmware as shipped should be fine with regard to clicks, on mine I have to disconnect the antenna in order to hear the clicks. ?If that's not true for you, I'd suggest a big electrolytic cap (47uF or bigger) across the 12v supply into the Raduino. ? ?Better yet, add a 50 ohm 1/2 Watt resistor between your +12v supply and the 12v input into the Raduino, then add that 47uF cap (or bigger) from the Raduino 12v to Raduino ground. From post 25393: ?I think some have been having success taming the tuning clicks with large caps, but here's a post that says a parallel combination of 0.1uf plus 0.001uf work fine: ??/g/BITX20/message/25081? Seems right, likely injecting RF noise, not audio. With the braid disconnected on one end, the coax still functions as an electrostatic shield of the signal. ?The braid must be connected on both ends if you expect the coax to be a 50 ohm transmission line at RF, you definitely want a transmission line for the antenna connection and perhaps for the DDS cable. ?(The Si5351 is actually a PLL based part, not a DDS. ?But the Bitx40 schematic says DDS so I'll go with that.) There are cases where having a single grounding point or bus bar in the system reduces noise issues, all ground wires go to that one point. ?That way the voltage drop due to heavy currents in some wire (perhaps into the IRF510), doesn't inject noise into other parts of the design (such as the Raduino). ?Also, loops of wire can act as loop antennas and pick up stray RF that might be floating about due to lack of shielding and lack of coax somewhere else (like that antenna port). ?The Bitx40 circuit board has a solid copper ground plane, that's the best defense against either of these cases. ?The wires to a separate assembly like the Raduino are to be looked at closely, but power supply filtering seems to solve that particular case. ?Keeping the wires short helps on ohmic voltage drops, twisting them together or using coax keeps them from picking up stray RF fields. In general, I figure the more grounds the better, ?a grid of short ground wires performs almost as well as a solid copper ground plane. ? But what works best in any particular situation is not always obvious, it can come down to just trying stuff. ?Where I really get worried about grounds is when I have two pieces of equipment plugged into two different circuits from the main household fuse box, a refrigerator kicking on somewhere can cause a spike of several volts between those two chassis grounds if the house safety ground wires are absent or are carrying current for some reason. Jerry, KE7ER On Sat, May 13, 2017 at 10:22 pm, Thomas Noel wrote:
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Not a bad idea, it could well help. ?Also shields around various parts of the main Bitx PC board, ?I don't think anybody here has yet tried it and reported the results. ?Most of us have adequate performance by just keeping the wires short, maybe twisting the critical ones. ? On Sun, May 14, 2017 at 06:18 am, Michael Babineau wrote:
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For what its's worth Shielded wire from the tune pot to the DDS RG174 from the PCB ant. to the SO239 or BNC (rg8X) When running the power wires run them down low on the Metal chassis...you can tape them down. I hope to shield if not encase the DDS from ?the main PCB.? I may add 1000uf with parallel 100 pF to the 12v power connector pin to ground. I removed most of the extra DDS wires.? I'm keeping those wires for future use since they have connector pins. Try to keep any wires from passing over or under the main PCB. So far my BITX is working and making QSOs.? I want to implement the CW mod ASAP so I can adjust my Match box for best SWR. Right now I have my Match Box set to where I have it set for my 100 watt rig for its SWR on 40. I also noticed last few BITX QSO contacts that the final gets pretty warm.. I put a 2"x2" 12v fan behind the heat sink ?I increased the size of the heat sink by 2x used heat sink compound and it gets warm with winded QSOs.? I run the fan from a separate 8v battery because that's what I have for now. Just remember to keep the heat sink away/insulated from ground!! ? My Bitx runs off a 12v 18AH battery because that's what I had.? The battery is sealed lead acid that I trickle charge using my Harbor Fright Trickle charger.? I don't leave my battery down in the shack on trickle charge 'cause I don't like doing that unless I'm around.? I also keep the doors open for air circulation.? The battery is sealed but..safety first. I noticed when my battery runs down to 11v + my power suffers for it of course ?5-6 Watts down to 3 watts.? May use my Harbor Freight DVM connected to watch the battery Sunday. Also important too ground to your station ground. I hope this helps. 73 WA9DOH On Sat, May 13, 2017 at 8:04 PM, W9ZIM <darrendude@...> wrote: It does seem like there could be a lot more in the Wiki page since there's a lot of valuable information sprinkled throughout this group that I suspect most people will never find, mostly because they don't even know to look for it! |
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Thomas Noel
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You're welcome.? The hand book can be a source of a lot of info. on contruction. I might aid that I'm planning on going that slightly heaver wire for power. WA9DOH PS I hope be on 7.179 there about at 2100 Chicago time zone On Sun, May 14, 2017 at 1:38 PM, Thomas Noel <tnoel@...> wrote:
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W9ZIM