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watermelonman 24th October 2008 06:21 PM

GSM interference
 
The GSM interference coming out of many audio systems drives me nuts. Is a system with a tube amplifier likely to be any better or any worse in this regard? I am not even really sure if the interference comes in at the amp, wires, or speaker, but I sure want to get rid of it. If tubes are still susceptible, would it be possible to shield a homemade tube amp from this effect?

coresta 24th October 2008 07:06 PM

Not at all, in any case , :( The GSM burst transmitting waves are very sharp and disturb any electronic device . The solution is to not allow these in your neighbourhood ;)

gofar99 24th October 2008 10:26 PM

Hi , If it is diy equipment, I would try ferrite beads on the inputs and outputs as well as the ferrite line cord clamp on filters. This can often block the signals from getting in. Another possiblity is if you are connected to a CATV system (for FM or share it with a HT system) you may have grounding issues. I had trouble with mine. There was a differential between the AC mains ground and CATV system (shouldn't be I know but....) I used an isolation transformer in the CATV line and all was well.

Hope it helps this sort of problem can be a nightmare.

jackinnj 25th October 2008 02:33 PM

Re: GSM interference
 
Quote:

Originally posted by watermelonman
The GSM interference coming out of many audio systems drives me nuts. Is a system with a tube amplifier likely to be any better or any worse in this regard? I am not even really sure if the interference comes in at the amp, wires, or speaker, but I sure want to get rid of it. If tubes are still susceptible, would it be possible to shield a homemade tube amp from this effect?
There are two reasons why tube amplifier might be better -- the first is that the power and output transformers have limited bandwidth over which to transmit the 860MHz frequency. (Of course, they have coupling capacitance which defeats this to some degree.)

As a ham radio guy I learned to deal with interference from transmissions on the many of the ham bands. Oftentimes, however, the problems could be traced to corner cutting on the part of the TV-Receiver. Sometimes it is defective tuning on the ham radio transmitter, or a poor keying circuit -- and chapters are written on dealing with these issues in the ARRL Handbook.

I looked at the FCC's web-site, and as per typical, (just like BPL which interferes with ham radio and emergency services), they turned a blind-eye to the issue of GSM interference.

Most of the time the problem can be relieved by ferrite beads on the input, placing a small capacitance on the input (220pF, 300pF), good grounding. Problem with high frequency data transmission (unlike voice, or analog) is that there are all sorts of harmonics which radiate up and down the spectrum.

coresta 25th October 2008 02:55 PM

I wrote any as i know from the time i was working for a GSM operator in sites acquisition ;)

Eli Duttman 25th October 2008 03:48 PM

Quote:

The solution is to not allow these in your neighbourhood

That option is not available in the USA. A Federal Statute forces municipalities to allow cell towers to be raised. Good, bad, or indifferent; Congress has preempted local decision making about this particular matter.

jackinnj 25th October 2008 04:06 PM

That's not necessarily correct. They still have to pass local zoning in the U.S. -- it's an accomodation, not an absolute right. No one cares if you put a cell tower on top of a building near the Cross Bronx Expressway, but they bloody well holler if Verizon wants to put one of their eyesores on the Maplewood Country Club (you know the type I mean, the faux-Douglas Spruce which sticks out amongst all the old growth oaks!)

The pre-emption through the FCC doesn't completely rid you of the locals -- ask the folks at WFUV in the Bronx who had to fight the Botanical Garden for years to move their tower. In the end the horsey-set from the NYBG paid WFUV to place it elsewhere.

It can be really hard to put up a ham-radio tower in a lot of burbs in the U.S.

NJ has about the worst RFI of any state I have lived in. The crud which is emitted off the NJ Transit Rail lines makes short-wave unlistenable at times, the power grid is extremely noisy, they use all sorts of RF devices for traffic signalling which knock out a.m. radio in places -- this all comes about as the stuff is ancient, NJ having been one of the earliest to have a grid.

Eli Duttman 25th October 2008 07:26 PM

Jack,

I work for the NJ Judiciary and I have occasion to see some of the opinions coming out of the Appelate Division of Superior Court. With VERY few exceptions the cell phone companies win. Unless the GSM outfits' engineers and planners are total boneheads, who fail to get technical ducks in a row, Federal Law trumps local zoning, etc.

Some pretty "hoity toity" towns have had GSM facilities shoved down their throats. If competent engineers can demonstrate a lack of coverage, only a little nibbling around the fringes is left for the municipalites. As a private membership organization, the country club you described can't be forced to accept GSM tenants. However, if the deal is sweet enough for the members to take it and there is technical sense to the placement, municipal officials are very hard pressed to successfully oppose the matter. NIMBY just doesn't work under Congress' scheme.

Jeb-D. 25th October 2008 07:46 PM

Quote:

The GSM interference coming out of many audio systems drives me nuts. Is a system with a tube amplifier likely to be any better or any worse in this regard?
All of my tube amps pick it up, I don't think they are significantly more or less resistant. I'm sure there are measures that can be taken to reduce this though. Perhaps a cage over top mounted components would help.

w5jag 25th October 2008 08:01 PM

Last spring I upgraded our At&T first generation Razors to an AT&T Tilt (mine) and a Palm Centro (wife), and can't recall hearing any RFI from either of these devices. The previous devices were pretty bad.

Win W5JAG


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