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Dittel FSG71 Radio / Squelch Questions



 
 
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  #1  
Old January 14th 13, 01:29 AM posted to rec.aviation.soaring
Bastoune
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Default Dittel FSG71 Radio / Squelch Questions

All,

My radio (Dittel FSG 71) Squelch seems to be a bit sensitive (but by design, cannot be adjusted by the pilot). In my case, when flying, the squelch is a bit sensitive and the “white noise” of the radio comes on at times, even when there are no communications received. I can always reset the Squelch by pressing and releasing the PPT button. The radio then goes silent for a while until a real transmission is received, or until the sensitive squelch problem reappears. I cannot reproduce the problem on the ground.

I have noticed that the problem gets worse when I connect my PCAS MRX to the 12V bus of the aircraft. The problem is not as bad when I run the PCAS off AA batteries. I have also a vario+pda connected to the same 12V battery bus.

- Can the Dittel FSG71 squelch be adjusted internally? (it can not be done externally via a knob)
- If my other equipment connected on the 12V creates noise, can I install a capacitor between the power leads going into the radio to reduce the noise?
- What else could be the source of this nuissance?

Thanks,

Bastoune

Note: I have another radio related question but will post it separatly.
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  #2  
Old January 14th 13, 02:35 AM posted to rec.aviation.soaring
John Carlyle
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Default Dittel FSG71 Radio / Squelch Questions

On Sunday, January 13, 2013 8:29:52 PM UTC-5, Bastoune wrote:
All,



My radio (Dittel FSG 71) Squelch seems to be a bit sensitive (but by design, cannot be adjusted by the pilot). In my case, when flying, the squelch is a bit sensitive and the “white noise” of the radio comes on at times, even when there are no communications received. I can always reset the Squelch by pressing and releasing the PPT button. The radio then goes silent for a while until a real transmission is received, or until the sensitive squelch problem reappears. I cannot reproduce the problem on the ground.



I have noticed that the problem gets worse when I connect my PCAS MRX to the 12V bus of the aircraft. The problem is not as bad when I run the PCAS off AA batteries. I have also a vario+pda connected to the same 12V battery bus.



- Can the Dittel FSG71 squelch be adjusted internally? (it can not be done externally via a knob)

- If my other equipment connected on the 12V creates noise, can I install a capacitor between the power leads going into the radio to reduce the noise?

- What else could be the source of this nuissance?



Thanks,



Bastoune



Note: I have another radio related question but will post it separatly.


I can't help with the Dittel squelch adjustment, but I can confirm that some Zaon MRX units will create noise when it is operated with external power. My older one did not, but my newer one sure did! Played a little with filters and chokes, to no avail, and finally sold the MRX. Good luck!

-John, Q3
  #3  
Old January 14th 13, 03:42 AM posted to rec.aviation.soaring
[email protected]
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Default Dittel FSG71 Radio / Squelch Questions

Hi Bastoune.

It sounds like your equipment is generating noise (not uncommon), raising the noise floor and breaking the squelch.
It is best to tackle these problems at the source, by limiting the noise being emitted. Noise filtering on the supply is one option. Just a capacitor is most likely not sufficient.
As Q3 says, even filters and chokes in the supply might not be enough, particularly if the radio is picking up RF noise and not supply noise.

If you cannot get to the root cause, then adjusting the FSG71M squelch threshold is possible.
See images of the internals and the schematic of the radio on my webpages:
https://sites.google.com/site/threeu.../dittel-fsg71m

In the schematic the potentiometer for the Squelch threshold is R428.
In the images, this potentiometer is just at the bottom right edge of the yellow band. There is still a speck of red paint visible on top of the white potentiometer turn plate.
There is a hole in the bottom cover over this potentiometer, but it is close to impossible to get a screwdriver exactly into the slot.
The easiest way is to remove the 4 screws of the bottom cover and remove this cover. Then you have easy access to this pot.

It is impossible/useless to make statements about other potential sources without knowing your exact system setup.
But in general, watch out for switch mode power supplies. Especially cheap small 5V USB cigarrette lighter adapters used to feed PDA's.
Also watch out for the basics: if you have a weak power bus (e.g. thin wiring that creates voltage drop or a bad ground) trouble shooting becomes very difficult.

3U

  #4  
Old January 14th 13, 03:57 AM posted to rec.aviation.soaring
Bastoune
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Default Dittel FSG71 Radio / Squelch Questions

3U,

Thanks for the info. First, it looks like I will be running my MRX off the AA batteries next year...

With that being said, since my squelch is still a bit sensitive (even with the MRX off the circuit), I'll be looking at other improvement opportunities (thin power wires, etc.). The PNA is now powered off a LX Nav V7 so I want to believe that it is not the source.

There was a time where the PNA was powered of a "cigarette lighter" 5V power supply and I can confirm that it was an RF hell...

Thanks,

Bastoune
  #5  
Old January 14th 13, 03:59 AM posted to rec.aviation.soaring
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Default Dittel FSG71 Radio / Squelch Questions

I had this exact same issue with the Dittel FSG71 and the Zaon.

Sadly a ferrite core connected as close as possible to the Zaon did not solve the problem. I went so far as to put a choke on the power line to the Zaon with capacitors, and still had the issue. Ultimately, the only solution that worked was running the PCAS of batteries.

There is a screw on the side of the Dittle FSG71 that can be used to adjust the squelch threshold up or down. But this is not something you can adjust in flight.

Chris
42DJ
  #6  
Old January 14th 13, 04:38 AM posted to rec.aviation.soaring
Bastoune
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Default Dittel FSG71 Radio / Squelch Questions

Chris,

The only exteriors side "potentiometers" that I see to adjust are the "Audio sidetone control" and the "Microphone Gain Control". I assume then that the "screw" you are refering to is internal to the box (as 3U is showing on his link). Correct?

Bastoune
  #7  
Old March 26th 13, 01:53 AM posted to rec.aviation.soaring
Bastoune
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Default Dittel FSG71 Radio / Squelch Questions

Thanks to 3U for pointing to me toward the R428 potentiometer. A small adjustment did the trick!

For those that have a hard time finding the potentiometer, here is a link from DG Flugzeugbau that shows the location of the said potentiometer.

http://www.dg-flugzeugbau.de/Data/TN.../1997-20-e.pdf

Thanks,

Bastoune

  #8  
Old May 2nd 18, 11:55 PM posted to rec.aviation.soaring
[email protected]
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Default Dittel FSG71 Radio / Squelch Questions

3U, I realize this is a very old thread but I also have a to low on occasion squelch issue with my FSG71M radio however getting it in and out is very difficult, so do you have any idea which way to turn the pot once I gain access and how far to turn it? I only want to do it once.
  #9  
Old May 8th 18, 02:01 AM posted to rec.aviation.soaring
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Default Dittel FSG71 Radio / Squelch Questions

Sorry, don't remember. My radio has been working OK since my last posting.
Doing it only once will be difficult if you don't have access during full operation (and during full exhibit of the interference)
I took the lid off the radio for a while to be able to adjust the squelch during operation.
With the lid on, it is close to impossible to find the slot in the potentiometer.
With the lid on and if operational, you cannot use a metal screw driver for the risk of mis-placing the tip and creating a short to the metal housing.
It is a single turn pot, so about 300 deg total range.
I would make adjustments in 30 deg steps.
3U.
  #10  
Old May 8th 18, 03:45 PM posted to rec.aviation.soaring
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Default Dittel FSG71 Radio / Squelch Questions

That makes sense. I was thinking that I would mark where the pot is now, turn it till it breaks squelch then go back past the mark and 30 degrees sounds like a good start.

Thanks
Cliff
 




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