Really good question.? When I was working on my receive signal issues I found those resistors were attenuating my signal a lot in the receive path,? I tested with and without them and I got a better receive signal with them in place.? Since in parallel they are dividing the resistance to reduce it a bunch
Parallel resistance measures 40 ohms at r17 (39 ohm resistor I think added to each by the colors I think) and 20 ohms at R37.? ? Not sure of the type since I pulled them off a very many many year ago high school project I found lying around.? They look bigger than my 1/4 watt resistors I bought recently.
I think those are in the receive path only so hopefully shouldn't impact my transmit issues.? I didn't have any surface mount resistors to add so went with those.
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On Sat, Feb 2, 2019 at 09:12 AM, Truffies wrote:
Question you have two big resistors to right and left of new L% and L& what are they and for and type?
-----Original Message-----
From: Dave Space <davesspacebar@...>
Sent: Feb 2, 2019 11:17 AM
To: [email protected]
Subject: Re: [BITX20] Spurs/Harmonics fixes for v4 based on v5 board design?
Thanks Raj.? I already replaced all 5 relays just to be safe with axicom ones and now also the L5 and L7 fix.? Would it be possible to add a low pass filter into the transmit chain somewhere to prevent that mixer product?
On Fri, Feb 1, 2019 at 10:14 PM, Raj vu2zap wrote:
What inductors did you use, please share a pic.
There is always a carrier leak at 12Mhz and 12-7 = ~5 Mhz could be what you see.
Most spurs are created by the harmonics of the carrier feeding back to the first BiDi amp. Changing to Axicom relays
eliminates a lot of these dancing dervishes.
Raj
At 02-02-19, you wrote:
Thanks I'll try the two tone test next. Tonight I replaced L5 and L7 Raj's fix to see if I noticed any differences. Using LSB on 7.15 into 40db attenuator get-55db main signal and I see some sort of spur at around 5MHZ that is about -85db, doesn't fluctate with voice it's constant when I key the transmitter. Wonder what could be producing around 5 MHZ.
I wonder if the v5 board redesign changes next might help. Might see if I can figure out where on the board that could be introduced.
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