My first post on Van's and I know this is a common problem, but I've exhausted ideas and read and rewired for two weeks. Could really use some insight!
Zenith 701, just doing Phase I test flights.
Radio is a Becker AR 3201 with built-in intercom.
Wiring diagram followed closely and assistance from hangar mate and other EAA guys. (hangar mate is an engineer with an RV-10 he built)
Antenna on belly of aluminum plane, isolated carefully. Coax connected well and shielding grounded at antenna base.
Radio clear, transmits well, intercom works well, everything working great....until take-off. A few feet off the ground, static begins. Loud static. Not a whine from alternator, but does seem to vary with RPM sometimes. Can hear faint "clicks" in headset when elevator trim tab button is actuated. Hard to hear others transmitting, due to constant static, but they report they hear me 5x5. If receiving a powerful transmission from another radio, it is clear. Most received signals are not strong enough to suppress all the static. On landing, radio clear again. No static. With full-power run-up on ground, no significant static.
Initially headset jack grounds and mic jack grounds were combined to one ground wire (shielded), which went to grounding block near radio.
Rewired, as we noted that wiring diagram showed these grounds to have pin positions into radio.
Fixed:
Headset and Mic jacks have grounds which terminate in pins into radio. PTT ground (shielded) goes to grounding block near radio. Headset and mic and PTT wires are shielded. Headset jack grounds connect with shielding and shielding goes to headset ground pin for radio. Mic grounds use conductor wire (shielded) to go to mic ground pin in radio.
Tried: (without benefit)
disconnecting intercomm.
adjusting squelch, intercomm level, single-sideband level (3 philips screw adjustments on side of radio case)
rechecking and further insulating antenna from aluminum skin.
took grounding connection off of coax shielding at antenna...leaving coax shielding not grounded. At this point, others could not hear my transmissions well at all. Transmission clarity was terrible.
reconnected shielding at antenna (angled whip antenna with design to have shielding grounded at antenna base) and moved antenna further back in aircraft (to get farther from generator -- Rotax 912ULS with proper resistor plugs and generator at firewall-side of engine--electronic ignition). My transmissions are clear again.
Connected hand-held rubber-ducky antenna to back of radio. Still same static.
connected radio to ELT antenna (coax), which sits on top of aircraft, behind cockpit.--THIS SEEMED TO CLEAR ALMOST ALL STATIC. Thus, I moved the radio antenna (under the belly) another two feet back from firewall (should be plenty far away from engine, ignition, and generator, at this location).
Still static.
I'm perplexed. The static is not characteristic of alternator "whine". Hearing the faint clicks of the trim switch being activated, makes me think there is something feeding radio signal from the airframe to the radio...but why fine on the ground?
If anyone has any insight into this, I'd be most grateful. My friend with the RV-10 suggested I try this forum, even though I have a Zenith
I suppose, if nothing else, I'll try again connecting to the ELT antenna and see if that really does clear it up. If so, I suppose I may try moving the antenna again, but several guys with more grey hair than me don't think it should have to be moved from where it is.
Thanks again for reading and any thoughts or ideas!
Zenith 701, just doing Phase I test flights.
Radio is a Becker AR 3201 with built-in intercom.
Wiring diagram followed closely and assistance from hangar mate and other EAA guys. (hangar mate is an engineer with an RV-10 he built)
Antenna on belly of aluminum plane, isolated carefully. Coax connected well and shielding grounded at antenna base.
Radio clear, transmits well, intercom works well, everything working great....until take-off. A few feet off the ground, static begins. Loud static. Not a whine from alternator, but does seem to vary with RPM sometimes. Can hear faint "clicks" in headset when elevator trim tab button is actuated. Hard to hear others transmitting, due to constant static, but they report they hear me 5x5. If receiving a powerful transmission from another radio, it is clear. Most received signals are not strong enough to suppress all the static. On landing, radio clear again. No static. With full-power run-up on ground, no significant static.
Initially headset jack grounds and mic jack grounds were combined to one ground wire (shielded), which went to grounding block near radio.
Rewired, as we noted that wiring diagram showed these grounds to have pin positions into radio.
Fixed:
Headset and Mic jacks have grounds which terminate in pins into radio. PTT ground (shielded) goes to grounding block near radio. Headset and mic and PTT wires are shielded. Headset jack grounds connect with shielding and shielding goes to headset ground pin for radio. Mic grounds use conductor wire (shielded) to go to mic ground pin in radio.
Tried: (without benefit)
disconnecting intercomm.
adjusting squelch, intercomm level, single-sideband level (3 philips screw adjustments on side of radio case)
rechecking and further insulating antenna from aluminum skin.
took grounding connection off of coax shielding at antenna...leaving coax shielding not grounded. At this point, others could not hear my transmissions well at all. Transmission clarity was terrible.
reconnected shielding at antenna (angled whip antenna with design to have shielding grounded at antenna base) and moved antenna further back in aircraft (to get farther from generator -- Rotax 912ULS with proper resistor plugs and generator at firewall-side of engine--electronic ignition). My transmissions are clear again.
Connected hand-held rubber-ducky antenna to back of radio. Still same static.
connected radio to ELT antenna (coax), which sits on top of aircraft, behind cockpit.--THIS SEEMED TO CLEAR ALMOST ALL STATIC. Thus, I moved the radio antenna (under the belly) another two feet back from firewall (should be plenty far away from engine, ignition, and generator, at this location).
Still static.
I'm perplexed. The static is not characteristic of alternator "whine". Hearing the faint clicks of the trim switch being activated, makes me think there is something feeding radio signal from the airframe to the radio...but why fine on the ground?
If anyone has any insight into this, I'd be most grateful. My friend with the RV-10 suggested I try this forum, even though I have a Zenith
I suppose, if nothing else, I'll try again connecting to the ELT antenna and see if that really does clear it up. If so, I suppose I may try moving the antenna again, but several guys with more grey hair than me don't think it should have to be moved from where it is.
Thanks again for reading and any thoughts or ideas!