Guys, I have a peculiar problem. Whenever there is a slight fluctuation in the supply line (Usually the AC Compressor kicking back in), for a fraction of a second there’s a click in my UPS (Powersafe 1kVA) and my DSL modem drops the ADSL line!
This is really annoying cause it reboots like every time there’s a slight drop.
Any idea if any surge protection or more likely some sort of power condenser that will hold the current steady for the slight time period.
Help will be highly appreciated!
I assume
If the above assumptions are true, it seems to be the fault of the UPS. It is supposed to give a uniform power to all the components connected to it. Even if AC power being supplied to it fluctuates. Can you temporarily get another UPS and try with it?
everyone with BSNL modems are having this issue…
A lot of solutions have been discussed , but we all seem too lazy to try them out 
Yes, both your points are correct. As for the UPs, tried it with a Generic 600VA and the Powersafe 1kVA. Will try it with a APC 500VA and post back.
@ greenhorn - Its a D-Link GLB-502T. Same thing used to happen with my Linksys WAG325N also.
Any other suggestions, please?
someone here was planning to buy a USB powered ADSL modem. I was planning to connect a big ass capacitor in parallel, but the disconnects are few and far in between, so didnt bother
I have the same router connected to APC BR-800 (have even connected it to the Numeric 1KVA). It d/c even at a very slightest distrubance. Whereas the no name router which am using for Tata Indicom, doesn’t have any issues.
So its mostly the issue with the router.
Err…
For a similar reason, i shifted my DSL-502T to the UPS temporarily and later moved the ADSL modem and phone charger to the UPS(powercom 600) via a power strip.
I don’t think i noticed any resets after that. 
(Power fluctuation as in the tubelight blinks for a moment, switching off and on, all in a second or less- but used to reset modem when connected directly to the wall socket. :S)
UPS is dying and so disconnected now- hopefully will be getting a big and good one soon.
I think even a simple surge protector from a good brand like MX maybe useful.
(Power strip (cheaper than the latter) = Surge protector minus the surge protection; noise filter same in both hopefully)
+1 yes i would say that the router is at fault. My beetel one works w/o such problems.
An ideal UPS would not let the modem know that there is any power fluctuation. Seems like there is no ideal UPS.
BIKeINSTEIN, are you saying that after connecting to UPS your router no more resets? Or is it the power strip that has made the difference?
I have solution to your problem.Modify LC Filter circuit inside your modem.
http://img182.imageshack.us/img182/8093/rectbr3ak6.gif
Open modem look for 9V AC Pin outs.Find out Rectifier circuit to 9V AC usually 4 Diodes Bridge circuit(otherwise 2 Diodes).Attach 25V 4700/2200 micro Farads Capacitor to DC Supply output from Rectifier.Function of Extra Capacitor is to serve voltage in flickering period missed by UPS.This worked for me 100% i have BSNL MT880 Modem😊
GLB-502T is plagued with many issues and this is one of them :P. DSL-502T didn’t have any issue afaik. Nothing wrong with UPS n all. Surge protector won’t help, for all i know its going to help only when high voltage happens to come.
@Anish - you could try using an Online UPS or a CVT (Constant Voltage Transformer ?? ). Both these should feed an accurate non fluctuating current to the hardware. Of course both these are expensive. 
i too have GLB-502T & i have connected it directly to ac …no problem as such…as no fluctuations:)
Hmm, I do have a CVT, its being used for my TV and AVR, will try with it though. Otherwise its a modem issue? One more reason to get a better modem then!
You can Surely try that One, Must give your Modem Some juice(I mean Power) to run for that Fraction of second.