If this is your first visit, be sure to check out the FAQ by clicking the link above. You may have to register before you can post: click the register link above to proceed. To start viewing messages, select the forum that you want to visit from the selection below. |
|
|
|
Thread Tools | Display Modes |
#11
|
|||
|
|||
Com Standing Wave Ratio?
Cabin leaks slightly during only the heaviest rain storms. We haven't been
able to find the leak. Not very wet, could have just been high humidity, not sure. Full story if nothing more than for the archives and to jog my memory: Airplane sat on the ramp at Key West a couple weeks ago while they got over 3" of rain during some pretty heavy storms. Islands to the north got up to 10" during the same period. After the rain stopped I went out to the airport to check the plane, noticed several drops on one of the vertical cabin support posts ahead of the pilots window. No wet carpets, no dampness or free moisture on the glare shield, no other water noted anywhere, but when I checked the avionics the #1 nav lit up with 188.88 on active and standby. When I turned the speaker on, nothing but static coming from the nav side of #1, same thing through headsets. Pulled both #1 and #2, no free moisture noted in the trays or on the radios or connections but it felt like 110% humidity in the cabin. Took #1 back to the hotel and placed it in front of a fan, no heat, for approximately 10 hours. Reinstalled it in the #2 slot before we departed, no static, nav now displayed normal, operated normal. Flew home with #2 in the #1 slot driving the autopilot. Refueled at Eufaula, AL after 3+ hours. Everything normal. Refueled again in Champaign, IL after another 3+ hours, everything normal until we leveled off after climb out. Then #2 in #1 slot started the pitchdown when transmitting with alt hold thing. Not severe, just a mild pressure on the yoke, but noticeable. Checked transmit on the #1 com (the wet one) in the #2 slot, no problems. Checked Nav vs Hdg mode on the autopilot, pitch down in either mode. Checked GPS vs VOR, pitch down when coupled to either source. Swapped them back to original locations after we got home. Next day flew some approaches with a friend, local tower complained of heavy static during transmissions from the #1 (wet) com. No pitchdown with this radio noted. No complaints of static prior to Key West flight. So I've got static on #1, and #2 causes pitch down, but no static, when installed in the #1 slot. Jim |
#12
|
|||
|
|||
Com Standing Wave Ratio?
Roy Smith wrote:
Tauno Voipio wrote: The ratio of voltage and current of a RF signal in a transmission line (called characteristic impedance) is fixed and determined by the dimensions and materials of the transmission line. Considering how much abuse the typical piece of coax absorbs over GOK how many years of being scrunched into the rats nest of wiring behind most GA panels, I suspect the characteristic impedance is anything but fixed. As long as the scrunch is short compared to the wavelength (in the cable, for coax about 2/3 of free-space wavelength), the signal could not care less, and, for practical purposes, the characteristic impedance is constant. If we have to take the attenuation into account, the impedance is not even real, but complex, containing capacitive or inductive components. Not to mention that a lot of radio guys barely know which end of a soldering iron to pick up. SWR Meter? That's the box which tells you how ****ty a job you did of putting the connectors on before you button up the panel and write out the customer's bill. You can also crash a new car before delivering it to the customer ... -- Tauno Voipio tauno voipio (at) iki fi |
#13
|
|||
|
|||
Com Standing Wave Ratio?
Jim Burns wrote:
Cabin leaks slightly during only the heaviest rain storms. We haven't been able to find the leak. Not very wet, could have just been high humidity, not sure. Full story if nothing more than for the archives and to jog my memory: Airplane sat on the ramp at Key West a couple weeks ago while they got over 3" of rain during some pretty heavy storms. Islands to the north got up to 10" during the same period. After the rain stopped I went out to the airport to check the plane, noticed several drops on one of the vertical cabin support posts ahead of the pilots window. No wet carpets, no dampness or free moisture on the glare shield, no other water noted anywhere, but when I checked the avionics the #1 nav lit up with 188.88 on active and standby. When I turned the speaker on, nothing but static coming from the nav side of #1, same thing through headsets. Pulled both #1 and #2, no free moisture noted in the trays or on the radios or connections but it felt like 110% humidity in the cabin. Took #1 back to the hotel and placed it in front of a fan, no heat, for approximately 10 hours. Reinstalled it in the #2 slot before we departed, no static, nav now displayed normal, operated normal. Flew home with #2 in the #1 slot driving the autopilot. Refueled at Eufaula, AL after 3+ hours. Everything normal. Refueled again in Champaign, IL after another 3+ hours, everything normal until we leveled off after climb out. Then #2 in #1 slot started the pitchdown when transmitting with alt hold thing. Not severe, just a mild pressure on the yoke, but noticeable. Checked transmit on the #1 com (the wet one) in the #2 slot, no problems. Checked Nav vs Hdg mode on the autopilot, pitch down in either mode. Checked GPS vs VOR, pitch down when coupled to either source. Swapped them back to original locations after we got home. Next day flew some approaches with a friend, local tower complained of heavy static during transmissions from the #1 (wet) com. No pitchdown with this radio noted. No complaints of static prior to Key West flight. So I've got static on #1, and #2 causes pitch down, but no static, when installed in the #1 slot. Jim The symptoms point to a bad contact somewhere. If there are socketed circuits on the boards, re-socketing them may be in order. A worse possibility with paper-based circuit board is that the base expands when wet, and this can break feed-through connections through the board (called vias in the jargon). I'd take the unit to a shop with measuring instruments to see if the 'static' follows the radio (and not the installation place). -- Tauno Voipio tauno voipio (at) iki fi |
|
Thread Tools | |
Display Modes | |
|
|
Similar Threads | ||||
Thread | Thread Starter | Forum | Replies | Last Post |
Standing room only ~ Is this a joke? | Flyingmonk | Piloting | 7 | April 27th 06 06:20 PM |
Another CLUSTER Fu*k by Thousands Standing Around | Whatdoyouexpect | Instrument Flight Rules | 0 | March 18th 06 03:28 PM |
Another CLUSTER Fu*k by Thousands Standing Around | Whatdoyouexpect | Piloting | 0 | March 18th 06 03:27 PM |
Voltage Standing Wave Ratio Bridge | SUIRE2 | Home Built | 1 | February 9th 06 03:10 PM |
American Airlines - Last one standing | Larry Dighera | Piloting | 42 | September 17th 05 04:50 AM |