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.

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

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

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

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.

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.

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

At 01:01 08 May 2018, wrote:

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.

Use a non-metallic trimming tool. They are not expensive.
As an alternative use a plastic knitting needle filed to a chisel-point
(but do a Risk Analysis Assessment first!)

On Wednesday, May 2, 2018 at 6:55:36 PM UTC-4, wrote:
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.

I just did this, FSG-71 in a Ventus B with S80. I think the S80 was the culprit. I opened the radio and turned the pot FROM 1:00 TO 11:00. It was my first try at an adjustment, just a total guess, and it seems to have worked perfectly. At least it works well on the ground, haven't flown with it yet. When I turn the radio on now, it breaks the squelch in about half a second. Thanks to the person who posted the schematic with the pot location.. I doubt I would have been able to keep the radio in the glider without that info.

Thanks Jim, I hope your having fun in the Ventus, Sold mine, kinda miss it but enjoy the handling of the 27