Crazy Radio Issue, Help Needed.
Psychophysiological entity
I wish I'd spotted this thread from the get-go. Fascinating.
Is it still an ongoing mystery, or is the fitting of the lower aerial considered a final fix/workaround?
I used to commute from the east coast to Luton, often at night in a 4 seat metal aircraft. It was fairly new, but the radio used to get worse as I passed near to Stansted, then improve with distance. I did exactly what I'd want to do with this problem, and measure the AGC voltages. However, in those days, I was able to open the box without breaking hidden seals.
In this case, after a few pages I have to not spend any more time today, but after so much testing and swapping - I was getting a gut feeling (after a C&G and being a telecom tekki) in my yoof, that something exotic was happening. Thinking laterally, I wondered if the basic design of the comms boxes radiated a spurious signal, which was being reflected by by a prop disc that only qualified as a dish at a certain RPM. I'd want to know what happened to that AGC line as the signal was swamped/diminished.
I know it was easy in my day. AGC feedback was a simple voltage that could be measured with an AVO. Now I suppose it's a digital 'statement.'
Is it still an ongoing mystery, or is the fitting of the lower aerial considered a final fix/workaround?
I used to commute from the east coast to Luton, often at night in a 4 seat metal aircraft. It was fairly new, but the radio used to get worse as I passed near to Stansted, then improve with distance. I did exactly what I'd want to do with this problem, and measure the AGC voltages. However, in those days, I was able to open the box without breaking hidden seals.
In this case, after a few pages I have to not spend any more time today, but after so much testing and swapping - I was getting a gut feeling (after a C&G and being a telecom tekki) in my yoof, that something exotic was happening. Thinking laterally, I wondered if the basic design of the comms boxes radiated a spurious signal, which was being reflected by by a prop disc that only qualified as a dish at a certain RPM. I'd want to know what happened to that AGC line as the signal was swamped/diminished.
I know it was easy in my day. AGC feedback was a simple voltage that could be measured with an AVO. Now I suppose it's a digital 'statement.'
Machaca, I don't understand the photographs you've posted. Is that aircraft actually airworthy? I've dealt with flying wrecks in the past but that is a bloody disgrace. Tell me it's not the one we're discussing here.
Another puzzle (hopefully resolved soon) (sigh......)
FOR
PS Please, no-one start posting photos of the bl**dy spark plugs
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Was this aircraft resurrected from a serious accident in 1984 or was the reg number later assigned to another FA-200-180?
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Registration details for hangflyer's aircraft are:
Model FA-200-180
Serial FA-200-203
First Registered Date: 07 November 2006
The accident report says the aircraft involved in the 1984 accident was destroyed.
Model FA-200-180
Serial FA-200-203
First Registered Date: 07 November 2006
The accident report says the aircraft involved in the 1984 accident was destroyed.
Last edited by mike-wsm; 1st Mar 2011 at 01:21.
Thanks for the continued stupidity DERG, you seem to have adopted Charlie Sheen's approach to life ---> "Nutter". 
I presume you are going to explain that these particular cockroaches have some kind of Adonis DNA and can sense when the radio is in-tune with a station and start generating 'white noise'.
Since not much useful has been added in 24 hours ('cept the electrical schematics perhaps) I will continue to remind all the folks that can't be bothered to read the ENTIRE thread, that much fault-finding has already been done and the single MOST IMPORTANT point discovered to date are these:
- No white noise with the engine RPM below about 2350 (was originally 2250, but went up a little following replacement of plugs and 'tune-up' bits in the engine
- ONLY NOISE when the tuned station is within +/-20 degrees of the nose, goes away otherwise
- ONLY NOISE when a station IS TUNED, opening the squelch on an open frequency does NOT produce the problem effect
- Noise is NOT heard on a hand-held in the cockpit, or the Nav receivers
- Noise is the SAME whether the station is the tower 200m away or many km distant, the receive volume of the noise is constant
- Noise is heard on BOTH VHF receivers (2 fitted), originally 2 antennas on topside rear of craft
- New antenna installed on the underside of the aircraft does NOT suffer noise
(There might be a couple of other pointers I'm forgetting but I think these are the key ones)
My dis-assembly of all this is:
a) Noise is not RF signal (otherwise hand-held and nav rx would 'hear' it too)
b) Noise is not RF signal (otherwise an open frequency would carry it too)
c) Directionality - prop is in front and effect is linked to RPM.... vibration effect???
d) ADF antenna is directly above topside location of original antennas... interaction?
What am I missing (DREG - again, if you mention cockroaches I have suggestions where to insert them....)
- GY
I presume you are going to explain that these particular cockroaches have some kind of Adonis DNA and can sense when the radio is in-tune with a station and start generating 'white noise'.
Since not much useful has been added in 24 hours ('cept the electrical schematics perhaps) I will continue to remind all the folks that can't be bothered to read the ENTIRE thread, that much fault-finding has already been done and the single MOST IMPORTANT point discovered to date are these:
- No white noise with the engine RPM below about 2350 (was originally 2250, but went up a little following replacement of plugs and 'tune-up' bits in the engine
- ONLY NOISE when the tuned station is within +/-20 degrees of the nose, goes away otherwise
- ONLY NOISE when a station IS TUNED, opening the squelch on an open frequency does NOT produce the problem effect
- Noise is NOT heard on a hand-held in the cockpit, or the Nav receivers
- Noise is the SAME whether the station is the tower 200m away or many km distant, the receive volume of the noise is constant
- Noise is heard on BOTH VHF receivers (2 fitted), originally 2 antennas on topside rear of craft
- New antenna installed on the underside of the aircraft does NOT suffer noise
(There might be a couple of other pointers I'm forgetting but I think these are the key ones)
My dis-assembly of all this is:
a) Noise is not RF signal (otherwise hand-held and nav rx would 'hear' it too)
b) Noise is not RF signal (otherwise an open frequency would carry it too)
c) Directionality - prop is in front and effect is linked to RPM.... vibration effect???
d) ADF antenna is directly above topside location of original antennas... interaction?
What am I missing (DREG - again, if you mention cockroaches I have suggestions where to insert them....)
- GY
Last edited by GarageYears; 1st Mar 2011 at 12:58. Reason: Mike-WSM correction on my rant regarding the aircraft age! Deleted the whole waffle - hope the pics are not a reflection of the current aircraft
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Last edited by mike-wsm; 1st Mar 2011 at 13:12. Reason: add 'first'
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From a web-site. VH-FJI is maintained in the Charter Category and is probably the finest example of a Fuji in WA.
I'm still baffled by Machaca's photograhs. They must be from a different aircraft - so why post them?
As I said earlier - 'I've dealt with flying wrecks in the past but that is a bloody disgrace. Tell me it's not the one we're discussing here'.
I'm still baffled by Machaca's photograhs. They must be from a different aircraft - so why post them?
As I said earlier - 'I've dealt with flying wrecks in the past but that is a bloody disgrace. Tell me it's not the one we're discussing here'.
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hangflyer
I would like to suggest a test, please. One of the explanations suggests that there is no external noise, and that the white noise you hear is just the normal internal radio mixer noise heard when the received signal gets very weak and the agc (automatic gain control) turns up the radio gain.
Would it be possible to check reception on a distant station and see if the noise level comes up and whether it sounds the same? To one side and using each receiver in turn.
Many thanks, Mike.
I would like to suggest a test, please. One of the explanations suggests that there is no external noise, and that the white noise you hear is just the normal internal radio mixer noise heard when the received signal gets very weak and the agc (automatic gain control) turns up the radio gain.
Would it be possible to check reception on a distant station and see if the noise level comes up and whether it sounds the same? To one side and using each receiver in turn.
Many thanks, Mike.
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I'm still baffled by Machaca's photograhs. They must be from a different aircraft - so why post them?
The images I've posted are indeed from photos of VH-FJI -- taken by hangflyer himself last June.
I'd be more worried about the control column coming off in my hands.
I really don't get it - the external condition doesn't reflect any of the mess that appears to be inside.
To be honest I'm surprised much of anything works. Ever heard the term ground-up rebuild??
- GY
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Thanks Machaca. There's something very fishy here. No one in their right mind would charter that mess - and surely the aircraft has an independent annual. Who would sign that off? Very very fishy.
I'm out.
I'm out.
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I'd be more worried about the control column coming off in my hands.
forget -- a lot of time passed since hangflyer acquired the aircraft and he subsequently offered aerobatic flights for hire. Much work could have been accomplished since last June.
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Alternator Regulator
It would appear that the alternator is a belt driven Prestolite brand, and the above schematic represents the associated regulator.
Potential noise culprits are the Zener diode Z1 (with open circuit C1) and L1 - a neon. MWR has dismissed the regulator, based on reports from HF, but as nothing has conclusively been determined as the cause, it is still open to conjecture.
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Please check the original post, a lot was already covered.
cwatters wonders
You mentioned it only occurs with the radio tuned to a station. Could this be some sort of coupling between the two radios? Does it only do it when both radios are on?
From HF original post:
You mentioned it only occurs with the radio tuned to a station. Could this be some sort of coupling between the two radios? Does it only do it when both radios are on?
Idea 10, Another Nav Aid or System. Everything except Com1 de-energised (including Alternator) so running off battery. No Change.
Moderator
We appear to have some remaining tech posts interspersed with a range of silly posts. I have had several complaints that the latter are spoiling the game for those more interested in the tech aspects.
I will monitor the thread more closely and, if the standard of some posts doesn't rapidly rise, either move the thread elsewhere or remove some posters as appropriate.
regards,
I will monitor the thread more closely and, if the standard of some posts doesn't rapidly rise, either move the thread elsewhere or remove some posters as appropriate.
regards,