Mystery Static Problem

[Citizen]

I want to describe a problem I am having with my GMRS communications, so maybe the experts on here could offer some ideas.  Out of respect for everyone’s time, I’ll first describe the issue, and my setup, so no time is wasted asking.  I’ll also describe a number of steps I’ve already tried (nothing worked), again so no additional time and effort is wasted suggesting something already tried.

 

Problem Description: Mystery Static Bursts during RX/TX

 

During Standby: No problem, no static detected, squelch not broken.

 

During RX: Occasionally I will receive a burst of static while someone else is modulating.  It seems to happen at random, maybe about once per minute and last for 3-5 seconds.  It is not enough to completely obliterate the receiving transmission, but enough to seriously degrade it.  It sometimes will also happen during receipt of repeater Morse code identification, but not every time.  Time of day does not seem to matter, morning, afternoon, evening, as this happens most times someone else is modulating.  So far, this only seems to happen on 462.650/467.650.  It is difficult for me to experience or verify this problem on other channels/frequencies due to little or no traffic on them in my area.

 

During TX:  Others have reported that while I am transmitting, occasionally they will hear a static burst on their end, similar to what I hear during RX, and sometime this static is strong enough to completely knock out my transmission.  It seems to happen at random, and again last for 3-5 seconds.  During long transmissions, the other person will hear me ok at first, then I may drop off completely mid-transmission, and then resume.

 

My Radio Setup:

• Setting:  Single family style residential brick home in typical subdivision
• Primary base-station radio:  AnyTone AT-588 – Power output setting: Middle (25w), WB setting: 20K
• Alternate radio:  Midland MXT115 – Power output setting:  High (15w)
• Antenna: Tram 1486 (trimmed for 462mHz), roof mount, approx. 20’ AGL
• Cable: LMR400 (approximately 36’ length, PL-239 connectors)
• Power Supply:  DuraComm (measured voltage 3.9v, constant)
• Excellent repeater reception/access (Dickenson Texas 650), with correct tones, LOS distance 15.5 miles

 

Other Notes:

• Wall penetration for cable routing to attic/roof contain 4 cables: 
  • 1) Primary GMRS antenna (Tram,  outside roof mount) 
  • 2) Alternate GRMS antenna (factory cut for GMRS, attic mount) 
  • 3) Scanner antenna (attic mount), and
  • 4) CB radio antenna (attic mount).
• Cable grouping above possibly runs near electrical outlet wiring.
• Tested with all radios off except one being tested.
• Tested with primary radio on, scanner on.  Radio experiences static bursts, scanner does not
• Tested after swapping primary/alternate radios.  Problem persists on new primary.

• Antenna cable routing is same for all radios and terminates in attic; except for the primary antenna cable continues higher to roof a penetration.
• All equipment is fairly new (within 3 months old)
• There are two laptop computers (one uses Bluetooth) and one printer nearby, but typically these are off during radio traffic.
• 900 mHz wireless telephone base nearby, originally in immediate vicinity but moved 8 feet away from radio and antenna cables.

 

Solutions I Have Already Tried:

1. Replaced primary radio.  I sent the AT-588 back, and they sent me a new one (verified by different serial nbr).  Problem persisted.
2. Replace alternate radio.  I had a second MXT115 in my truck, so I swapped them.  Problem persisted.
3. Grounding antenna:  Ground wire run from antenna base to attic mounted ground (distance to house earth ground impractical to reach).
4. Conductive isolation of antenna from mast and removed ground.  Normally per instructions, antenna is bolted to metal mast with supplied connectors.  Thinking the mast may be holding static electricity, I insulated the antenna from the mast using pieces of rubber.  The mast itself is bolted to wooden roof with composition shingles.
5. Alternate Radio, but using same antenna/cable:  See primary and alternate radios above.
6. Scanner backup:  Using a separate scanner tuned only to 462.650, the scanner does NOT pickup the static burst.
7. Moved home Wi-Fi router and wired hub away from radio and antenna cables.  Previously in same vicinity, move to about 8 feet away.  Attempted to (temporarily) shield radio from WiFi signal using aluminum foil.
8. Moved home wireless phone system away from radio and antenna cables.
9. Reroute antenna cable in attic by unraveling/un-coiling excess to help eliminate possible bleed-over.
10. Swap out power-strip feeding power supply/radios.

 

Things I Have NOT Yet Tried:

1. Moving primary/alternate radios some distance away from the power supply (due to time or practical matters).  Currently power supply is right by radios.
2. Complete shutdown of all electronics (including lights) in radio room.
3. Replacing LMR400 cable (could be needless expense, since the one I am using seems good)
4. Replacing antenna (same as above, could be needless expense)

 

Recap and Summary:

I am experiencing unidentified static bursts on frequency 462.650/467.650.  Appears to be isolated to antenna/cable, or some type of nearby house electrical problem.  I’ve been dealing with this for some time, and am running out of things to try. 

 

Thanks in advance to anyone who can offer suggestions.  This is truly frustrating.

 

...

 

[mbrun]

A gremlin indeed. While you will invariable receive loads of ideas, I will start by throwing out the first one that came to my mind. Do with it what you will.

 

Confirm you have a set of conditions that are repeatable every single time.

 

Turn off AC power circuits in your home, except the circuit needed to perform your tests. Confirm if the symptom persists. It it does not persist, something powered by one the circuits you turned off is contributing. Power up one circuit at time until you find a circuit that results in the symptom occurring again. Then troubleshoot further by removing power (unplugging/removing) items from that circuit. Once you find the culprit, then we talk solutions.

 

If turning off circuits except the one needed for your tests does not yield results, then troubleshoot further by removing power (unplugging/removing) items from that circuit. Do this one at time until you find the culprit. Once you find the culprit, then we talk solutions.

 

If removing items from test circuit does not yield results and the only thing left connected is the offending radio, then starting powering down all battery operated devices in your home, including any device powered by a UPS. This includes cell phones, iPads, laptops etc... Blasts of GSM noise from a phone has been a common source of interface in the past and can be suspect. You could have other items in your home that contribute interference in a similar way.

 

I am one that most generally likes to remove all variables and build back up until the problem occurs. In this case I am taking a hybrid solution.

 

Hope there is a nugget of help in there for you.

 

Michael

WHRS965

KE8PLM

 

 

Sent from my iPad using Tapatalk

[gman1971]

Another idea, try buying an UHF preselector, what you are experiencing seems to me more like intermod due to strong RF signals coming from nearby "angry RF firebreathing broadcast towers" and blitzing the receiver...  Most of my earlier radios suffered from this issue, the NOAA @ 162.550 kept popping in the middle of weaker transmissions, or when no signal was present... the solution for me was to buy LMR commercial gear radios with tuned front ends... no more intermod problems since.

 

G.

[AdmiralCochrane]

Yeah, if he is very close to one of the Galveston TV transmitters or police/ems or private com towers, the interference becomes likely. 

 

In my area we have occaisional harmonic problems 

[WRAK968]

Check two things, 1) Check that cell phones are away from the radio, 2) check that Wifi transmitters are away from the radio, see if this fixes the problem. I recall having similar issues when on EMS calls with our VHF radios. It was enough to mess with the transmission and if the signal was weak, would kill the transmission outright, and would last anywhere from 1-5 seconds, (longer when receiving data or text) The same happens if you have something using wifi that is close to the receiving radio though it'll happen much more often.

[Citizen]

Thanks Michael.  I had not considered shutting down various other home AC power circuits for my tests.  I’ll try it somehow, but it will be difficult (wife probably not going to appreciate me shutting down her internet/satelliteTV/phone/lights just so to test my radio system, but maybe I’ll wait till she’s napping, ha).  Some good nuggets there and your hybrid method seems like a sound approach.

 

And thank you also Gman and Admiral:

I am 11.2 km (6.95 miles) LOS from the Greater Houston antenna farm.  Wow!  I don’t know why I didn’t think about it before.  Here is some info from the internet about the farm:

 

“…eight antenna towers that provide television and FM radio broadcast capabilities for the Greater Houston area, serving 46 television stations (including digital, low power and translator stations), and 23 FM radio stations.”

 

Two of the towers there are about 2000 feet high and so must be some of those “angry RF firebreathing broadcast towers” Gman was talking about.  Being only 7 miles away, it’s likely I’m being blitzed as you suggested.  This does explain some things, but it also leaves me with a few more questions. 

• Are the static blasts I’m receiving simply bleed-over from other frequencies, and not actually on 462.650?

• What triggers the blasts?  They only seem to occur randomly while someone is modulating, never during standby, and only last for 3-5 seconds, maybe once per minute or two.

• Why only is my one antenna is being affected?  Is it because it is the highest, and is external to my house/roof and thus the best for receiving?  The lower, inside the attic mounted antenna is not picking up the blasts even when I swap my primary radio to use it.

I didn’t know what intermod was, or a preselector, but after you mentioned it, I Bing’d it and now have an idea.  I found THIS article on Intermodulation.  It is a long read, and way over my head, but the first section on “Symptoms” helps me understand things better.  A preselector could be a solution (albeit not a cheap one).  Such is my luck living so close to the fire-breathers (Gman, you've coined a new phrase).

 

And thank you too WRAK968.  I did try shutting down and moving my cell phone away from the radio (but not my wife’s phone because she stores it some 25+ feet away from my radios, but perhaps I’ll revisit that).  And I did move the Wifi as far away as I could, about 8 feet (side note: this seemed to have helped for a day or so, static burst volume was reduced, but not eliminated, and the test was inconclusive because the higher volume bursts returned the next day….I don’t know what to think of that).

 

I’m not giving up.  The fight goes on.  Thanks much guys, for all your input.  I very much appreciate this myGRMS.com website and you pros who respond to people with issues like mine.

 

Thomas

 

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[Bow]

Just Curious, do you get the bursts with the antenna disconnected?

 

I might have missed where you tried that

 

Are the Blasts timed, or do they have a random pattern?

[RDH]

I had something similar to that on my murs HT's. I ended up finding the source was my power tool battery chargers. I took a handheld shortwave radio and went around the house waving the antenna around various electronics until I heard strong static. Relocating them to another area fixed my problems

[Citizen]

Just Curious, do you get the bursts with the antenna disconnected?

Are the Blasts timed, or do they have a random pattern?

 

Well, when I disconnect the antenna, I get no audio at all, and because the radio is receiving no modulation, there are no blasts.  The radio is completely silent. 

 

I tried to time the blasts, both in duration and interval.  There was no precise pattern with respect to when they occur, except that the seem to occur about once every minute or two, but ONLY WHILE SOMEONE IS MODULATING (silent otherwise).  And, the blasts last from 3-6 seconds.  And...people listening to me report that they hear the blast only sometimes during my transmission.  No pattern reported.

 

I had something similar to that on my murs HT's. I ended up finding the source was my power tool battery chargers. I took a handheld shortwave radio and went around the house waving the antenna around various electronics until I heard strong static. Relocating them to another area fixed my problems

 

Thanks for your post.  I decided to order up an RF sniffer (wanted one anyway), which should help me identify where the static blasts are coming from, IF they are coming from my own home. The sniffer should arrive by next Monday, then I'll make like Sherlock Holmes and see what I come up with.

 

...

 

[gman1971]

Intermod is exactly like that, bursts of energy. I know the problem well, sadly. Is not cheap to address it...  To begin with, you'll need a preselector, at least if you just want to "get by" for the time being, but after a while you realize that nothing but top end radios are going to give you the range you seek (if you want to have your own radio network). I have Vertex Standard on all my infrastructure radios/repeaters, the EVX-5300 have a 5 varactor tuned front end, good, but not enough and required an additional EMR preselector, otherwise in weak coverage areas I was getting blitzed with a lot of RF mixed up... thus range sucked... I have to say: never underestimate the power of those "RF firebreathing angry towers"... At 6 miles its signals shows up like a  -10 dBm signal on the radio front end, without any filters, it goes right through and wrecks all kinds of havoc inside the 1st stage...

 

Glad it could help.

 

G.

 

Thanks Michael.  I had not considered shutting down various other home AC power circuits for my tests.  I’ll try it somehow, but it will be difficult (wife probably not going to appreciate me shutting down her internet/satelliteTV/phone/lights just so to test my radio system, but maybe I’ll wait till she’s napping, ha).  Some good nuggets there and your hybrid method seems like a sound approach.

 

And thank you also Gman and Admiral:

I am 11.2 km (6.95 miles) LOS from the Greater Houston antenna farm.  Wow!  I don’t know why I didn’t think about it before.  Here is some info from the internet about the farm:

 

“…eight antenna towers that provide television and FM radio broadcast capabilities for the Greater Houston area, serving 46 television stations (including digital, low power and translator stations), and 23 FM radio stations.”

 

Two of the towers there are about 2000 feet high and so must be some of those “angry RF firebreathing broadcast towers” Gman was talking about.  Being only 7 miles away, it’s likely I’m being blitzed as you suggested.  This does explain some things, but it also leaves me with a few more questions. 

• Are the static blasts I’m receiving simply bleed-over from other frequencies, and not actually on 462.650?

• What triggers the blasts?  They only seem to occur randomly while someone is modulating, never during standby, and only last for 3-5 seconds, maybe once per minute or two.

• Why only is my one antenna is being affected?  Is it because it is the highest, and is external to my house/roof and thus the best for receiving?  The lower, inside the attic mounted antenna is not picking up the blasts even when I swap my primary radio to use it.

I didn’t know what intermod was, or a preselector, but after you mentioned it, I Bing’d it and now have an idea.  I found THIS article on Intermodulation.  It is a long read, and way over my head, but the first section on “Symptoms” helps me understand things better.  A preselector could be a solution (albeit not a cheap one).  Such is my luck living so close to the fire-breathers (Gman, you've coined a new phrase).

 

And thank you too WRAK968.  I did try shutting down and moving my cell phone away from the radio (but not my wife’s phone because she stores it some 25+ feet away from my radios, but perhaps I’ll revisit that).  And I did move the Wifi as far away as I could, about 8 feet (side note: this seemed to have helped for a day or so, static burst volume was reduced, but not eliminated, and the test was inconclusive because the higher volume bursts returned the next day….I don’t know what to think of that).

 

I’m not giving up.  The fight goes on.  Thanks much guys, for all your input.  I very much appreciate this myGRMS.com website and you pros who respond to people with issues like mine.

 

Thomas

 

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