There's some confusion about just how many birdies the AR8k has. One review said that it was relatively birdie free, but an archived copy of Rich Well's review said he found 253 of them between 25-1300 MHz, but that "Later models were fitted with better internal shielding which supposedly dramatically reduced noise and therefore the number of birdies." His test AR8000 had a serial number of 203xx.
My AR8k is a fairly late build, with serial number 547xx - but it still has an aviary of birdies inside there! I count 261 birdies between 5 & 1000 MHz. Looking at what crystals are fitted within, it appears as if about 60% of the birdies are related to the harmonics of those crystals. There's a 12.8 MHz reference, 4.9152 MHz for the microprocessor, 44.595 MHz for the 2nd local oscillator in AM/NFM/SSB modes, and a 34.350 MHz one for WFM 2nd local oscillator. As an example, the birdie near 983.050 MHz is a 200th harmonic of the 4.9152 MHz microprocessor crystal... 200th harmonic!!!
I tried the mod to replace the 4.9152 MHz micro ceramic oscillator with a crystal type, and contrary to popular belief, this doesn't reduce the birdie count, it only makes those birdies harmonically related to 4.9152 MHz more stable & less drifty.
I've also had a go at improving the shielding: an extra layer of nickel paint coating the inside (the original was a bit thin & patchy in places) and more shielding around the microprocessor & IF boards with copper shim. Also found out that earthing the crystal cases makes very little difference to the strength of the birdies generated.
Does anyone have one of these mythical 'fewer birdies' AR8000s and care to share the secret, perhaps take some photos of the PCBs within so we can work out how to quieten down the birdies?
My AR8k is a fairly late build, with serial number 547xx - but it still has an aviary of birdies inside there! I count 261 birdies between 5 & 1000 MHz. Looking at what crystals are fitted within, it appears as if about 60% of the birdies are related to the harmonics of those crystals. There's a 12.8 MHz reference, 4.9152 MHz for the microprocessor, 44.595 MHz for the 2nd local oscillator in AM/NFM/SSB modes, and a 34.350 MHz one for WFM 2nd local oscillator. As an example, the birdie near 983.050 MHz is a 200th harmonic of the 4.9152 MHz microprocessor crystal... 200th harmonic!!!
I tried the mod to replace the 4.9152 MHz micro ceramic oscillator with a crystal type, and contrary to popular belief, this doesn't reduce the birdie count, it only makes those birdies harmonically related to 4.9152 MHz more stable & less drifty.
I've also had a go at improving the shielding: an extra layer of nickel paint coating the inside (the original was a bit thin & patchy in places) and more shielding around the microprocessor & IF boards with copper shim. Also found out that earthing the crystal cases makes very little difference to the strength of the birdies generated.
Does anyone have one of these mythical 'fewer birdies' AR8000s and care to share the secret, perhaps take some photos of the PCBs within so we can work out how to quieten down the birdies?
