Re: Ashhar Farhan #ubitx
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Folks As you modify these PCB's to correct spurs and such remember; Adding new?PCB's and or daughter boards often inject new noise sources. and may disrupt existing signals.? Placement? and integrity of new boards will affect the UBITX.? So approach this effort with care. 73 Bill de kd5yyk From: Jerry Gaffke via Groups.Io <jgaffke@...> To: [email protected] Sent: Tuesday, December 4, 2018 12:04 PM Subject: Re: [BITX20] Ashhar Farhan #ubitx Curt wrote >? Do expect you will need some mods to correct spurious - the conservative approach >? seems to be a daughter board hosting an added set of relays, and some additions to the 45 MHz filter. Harmonics could be fixed by an external daughter board with relays and transmit low pass filters, duplicating what KT1,KT2,KT3 and L11 through L22 are supposed to be doing. Some forum members have created circuit boards that they sell as a kit to do this. Alternately, just replace the KT1, KT2, KT3 relays with Axicom relays, This is probably the preferred method for fixing harmonics if you can figure out how to remove the old relays. Harmonics are unwanted transmissions that occur at integer multiples of the desired frequency. Some might use the term "spurs" to refer to harmonics. Most people here use the term "spurs" to refer to any unwanted transmission that is not a harmonic. Spurs?are addressed in this thread of 60+ posts: ? ??/g/BITX20/message/61645 In that first post of the thread, Farhan writes: >? 4. With the relays that are now used for ubitx,? the harmonics at 3.5, 7 and 10 are in under -45 dbc. we don't need the axicom relays. From that, I assume that a uBitx shipped today from HFSignals has new relays, appropriate for RF switching. Unfortunately, no mention there of how to determine if your uBitx has old or new relays.? The relays on my first run v3 board of a year ago are of the "Virtual" brand, model VRS2H-S-DC12V-C. I'd guess that if the relays on your rig are some other brand, then you have the new relays. None of this is really nailed down yet well enough for somebody with a uBitx and DVM to be sure his rig is legal.? We need to know: 1)? Exactly which uBitx boards need the relays swapped out to Axicom? 2)? Exactly what parts should we procure for relay replacements and spur filters? 3)? Exactly how should those spur fix parts be installed on the board?? (With photos) Farhan recommended toroids for the spur filter inductors, Raj has found that shielded surface mount inductors work. Cheap standard issue surface mount inductors are apparently not sufficient. ? Rather absurd that this has not yet all been resolved to a recommended list of part numbers and step by step procedure for installing them. It's been months. Jerry, KE7ER ? |
bill wright