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Author Topic: Need help with 10 meter TVI problem!!  (Read 627 times)
NEW2THEHOBBY
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Posts: 7




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« on: November 23, 2002, 02:28:40 AM »

I just moved into a new QTH, and am experiencing some TVI problems.  I'm running a Uniden HR 2510 on 10 meters into a Solarcon IMAX A99 with 50' of mini 8U cable. My antenna is mounterd on a porch, and every time I transmit it totally wipes out all TVs in the home! (We are using a standard TV antenna mounted on the roof, about 20 feet from my transmitting antenna!)  Any recommmendations for a really good TVI filter?  Thanks!
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N6TGK
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Posts: 52




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« Reply #1 on: November 23, 2002, 02:46:18 AM »

NEW2THEHOBBY,
 I'm just wondering, you state you're using an HR-2510 on 10 meters with an IMAX A99 but I didn't see a callsign listed.  Are you even actually licensed to use the 2510 on 10 meters?

The IMAX A99 is also an Antron 99 or a Shakspere Big Stick.  Back when I was into CB back in the 80's, these things were called "bleed sticks" because they got into everything.  The only thing I can think of is to make sure the antenna is as high as possible and that you're equipment is grounded...each piece of equipment should have it's own ground wire going from the equipment to ground.  This eliminates ground loops.  A low pass filter in your transmission line might help some more.

If you're not licensed for 10 meters then I suggest you stay below 10 meters.  I'm not one to preach how to operate on CB, I just ask that any non-licensed people stay off 10 and 12 meters.
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WA4PTZ
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Posts: 528




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« Reply #2 on: November 23, 2002, 06:37:18 AM »

Sounds like a high- pass filter for the transmitter
and low-pass filters for the TV's. Also, a good
ground for the antenna and another location, as far
away from the TV antennas as possible. Also...
get rid of the RF AMP (Linear) and the amplified
microphone. If you are not using a amplified mic
then you may have the mic gain too high.
I hope you are licensed as well, Riley likes fresh
meat.
73 - Tim
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W5RB
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Posts: 564




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« Reply #3 on: November 23, 2002, 08:47:38 AM »

It'd help to know some specifics here .Does it affect picture , sound , or both ? Which channels are affected ? Is it worse on some channels than others ? What is the SWR of your antenna ? Has the radio been modified or retuned ? How is the TV signal wired to the sets in the house ? It shouldn't be hard to fix your problem ,just need a little more info.

Russ , W5RB
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KE3GK
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Posts: 12


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« Reply #4 on: November 23, 2002, 08:55:41 AM »

Come on Steve ... Just because he's running a easily converted to 11m rig, with a CB antenna, with a possible over-driven power mic (probably the cause of his TVI), and does not give a callsign - doesn't mean that he is a CB pirate.

Does it ?
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AB8IG
Member

Posts: 131




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« Reply #5 on: November 23, 2002, 10:48:08 AM »

NEW2THEHOBBY,
Easy fix.
Replace your CB antenna with an MFJ-260C. VSWR is 1:1 across the 10m band. It's small, easy to install and it's the perfect antenna for your Uniden.

Jim
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WG7X
Member

Posts: 350




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« Reply #6 on: November 23, 2002, 12:25:47 PM »

Guy! Guys! Guys!

Please don't be so quick on the trigger with those sarcastic replies!

No where in the initial request does "New2thehobby" mention linear amps or "power mics"!

Going off half-cocked is not helping with the problem. If this fellow is not licensed, you have just given him ample reason to never become licensed.

That being said, the solution here is to ensure that the transmitting antenna is not too close to the TV RX antenna. Also ensure that your are using the MINIMUM power necessary to communicate. If I remember correctly a Uniden HR-2510 is a 25 watt rig. If the power can be turned down, do so. Use good quality coax such as RG-213. Make sure that your coax is at least 99% shielded. Most cheap coax is lacking here and it can cause problems.

Try to get a good RF ground. An RF ground is not the same as your power line ground. A fair RF ground can be a quarter-wave length of wire attached to the ground on the rig. This is called a counterpoise.

I really think that the biggest problem here is the close proximity of your transmit antenna to the TX receive antenna. The fellow who mentioned the Antron being a "Splatter stick" is on the right track. This antenna apparently has a good low angle of radiation. This is great for DX, especially if the antenna is mounted high and in the clear. Unfortunately, this can cause problems such as you are experiencing if the antenna is mounted low and close to susceptible appliances.

Good luck with it...

73 Gary WG7X

PS: If you are NOT currently licensed, please consider becoming licensed. If you ARE licensed include your call sign when asking for help. This will help calm the cynical OT's out there who are always on the lookout for a CB'er to BBQ!

Sometines we can be very short with someone whom we suspect to be asking for advice on CB type problems on an Amateur radio web site. This is because in the past, this has caused problems for the Amateurs.

So we are fairly cynical these days...
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KA4WJA
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Posts: 704




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« Reply #7 on: November 23, 2002, 12:27:45 PM »

Al,
Chances are that you are interferring with your TV's because of "front-end overload"......
BUT, Russ, W5RB, is correct...we need MORE information to give you an accurate answer.....

{proper grounding is always a good idea....but in your situation, poor grounding may not be a proximate cause of your TVI....}


To give you some ideas....

1) If the TVI is on ONLY some channels, such as TV ch. 2, ch. 6, ch.10.....(and "possibly" ch. 7, 15-17, 19-22, 24-27, 29-32..) then it is probably "harmonic interference...and a "Low-Pass Filter" at your transmitter output will be of great help!!!
(they are cheap and available on the used market for about $25...)

[One note about "harmonically caused" TVI....It IS possible, and it DOES occur....even if you don't have much in the way of harmonics radiating from your transmitter.......In MANY TVI cases with TV antenna-mounted "pre-amps", these "pre-amps" can be pushed into "non-linear" operation, and/or severely overloaded by your ham radio signals...and the TVI may be a "combination" of front-end overload AND harmonic interference....therefore a "Low-Pass Filter" on your 10m rig may indeed be over great help, even IF your harmonic radiation is well within spec.........and/or you determine that the proxiamte cause of your TVI is front-end overload, a "Low-Pass Filter" is still a good idea...]

2) If the TVI is on all (or almost all) channels....then is is most probably "front-end overload"......NOT harmonic interference, so a "low-pass" filter in your transmission line ("mini 8U") will be of questionable success.....
Typically you'll need to move and/or "reposition" both antennas......
[although it is "possible" that "high-pass filters" attached to your TV sets (or "amplifiers") would be of some help.....they might not be successful at all..]

3) If you have a TV antenna-mounted "pre-amp" (or any kind of TV signal amplifier in your house...such as a "distribution amp", "amplified splitter", etc...), I'd suspect that is where the "overload" is occuring....
Simply "bypassing" them (or even just "unplugging" them form the AC line) is a very quick and easy test....

4)  Antennas by themselves, DO NOT cause TVI!!!  (But some are more prone to feedline radiation, harmonic radiation, etc.....BUT plaese remember, Antennnas do NOT casuse TVI.....)
 You may be experiencing some TVI caused by "feedline radiation"....(although probably NOT the "primary" casuse, it is possible...)
This "feedline radiation" can be cured by using a "line isolator", "current balun", or a "choke-type balun" at the antenna's feedpoint.....(typically 8-10 "ightly wrapped" turns of coax around a 4" form will suffice for the higher HF bands....)
Although I'm NOT personally familiar with your IMAX A99....but if it is, in fact, a "coaxial vertical dipole" (as the Shakespear "Big-Stick"), then it is certainly a canidate for a "choke"/"balun"/etc....
Since this type of antenna is know to have "feedline radiation" troubles.....I believe that some have designed a "de-coupling" section, that attaches to the antenna feedpoint, runs down a few feet (a 1/4wave???) and has a "choke", and/or a set of "de-coupling" radials.....I'm not sure, but this might also be marketed commercially....


5) Another possibility is that your 10m signals are getting into VCR's and/or DVD players attached to the TV's?Huh??  and/or the A/V cables attaching these devices?Huh??

6) It is also possible that you are interferring with the TV sets by getting into the TV's IF (41mhz-46mhz)...

7) Although it is NOT common for TV's attached to outdoor antennas to experience "common-mode interference" (since the "front-end overload" is almost always the case), it is "possible"....
"Common-mode interference" is casused by RF getting into your TV sets, via the AC power cords, etc...
These cords are acting as antennas, and "receiving" your 10m signals, sending them right into the TV set...

Al, as you can see, there is a fair amount of info that we'd need to know in order to narrow down the possibilities.......
But, as I wrote above, "front-end overload" is my "best guess"....
AND, if that is in fact the case, it IS possible that the only true cure will be moving your antennas further apart.....moving your 10m antenna "higher", as well as "further away" is also good!!!!

Please give us some more info....and hopefully someone here will be able to guide you in the right direction....

Al, also, please accept my apologies for some of the other responses you've gotten.....It seems that some hams have forgotten two inportant things:
1) The "Presumption of Innocence"...(innocent until proven guilty..) and
2) Even if you are/were operating on 11 meters, that doesn't mean you don't deserve some assistance with your problem......

WELCOME TO HAM RADIO!!!!

Good luck.
73,
John,    KA4WJA





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AB8IG
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Posts: 131




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« Reply #8 on: November 23, 2002, 02:18:11 PM »

I'm sorry for being sarcastic, I guess I am a little short tempered today.

1) Make sure that your coax and connectors do not have any resistance or open circuits. Your RF might not be getting to your antenna!

2) Solarcon makes a radial kit for that antenna. You might try attaching a few radials to it and see what happens (coax center to the vertical, shield to the radials).

3) Definitely use a low pass filter between your rig and its antenna before putting high pass filters on all of your TV sets.

Jim
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KI8DJ
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Posts: 190




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« Reply #9 on: November 23, 2002, 03:14:30 PM »

I don't buy that stuff about the a-99 splattering. I have used one for years and it caused the least tvi of many antennas i've used. Ameco makes or should I say sells a good high pass filter it helps a lot even with overload.It  also helps to have the antenna above the tv antenna so the main field of radiation isn't directly into the tv antenna. Make sure your 2510 hasn't been tweaked up as this can increase spurious emissions.Welcome to the hobby and if you're not a ham yet I'm sure you soon will be.By the way I started on cb recruited several good operators from the ranks,and still use it for casual chats with local folks 73 Gary ki8dj
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WB2WIK
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Posts: 20611




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« Reply #10 on: November 25, 2002, 11:22:13 AM »

Antennas don't "cause" TVI, transmitters do.

Proximity effects are very noticeable, and if one installs the A99 or any other antenna within 20' of his TV antenna, this is just begging for trouble.

Of course, the easiest solution for most is to switch to cable TV, or a DBS system like DirecTV or Dish Networks, all of which are extremely difficult to interfere with.  In lieu of that, move something!  Relocating either the 10m antenna, or the TV antenna, or both, is often the best, easiest and cheapest solution for TVI problems.  Get them as far apart as possible, and not in the same horizontal plane.

WB2WIK/6
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AD6JN
Member

Posts: 172




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« Reply #11 on: November 25, 2002, 12:08:38 PM »

Sounds like front end overload.  As long as there is a TV antenna it probably cannot be solved.  Maybe a differential mode filter on each set will work.  

Here is what I suggest.  

1.  When transmitting turn off or don't use the TV sets.
2.  Get cable TV and make sure the coax shield is grounded properly.
3.  If you get cable TV remove the TV antenna as it may cause additional problems.

The ARRL book on RFI explains all the details especially the front end overload.

Bob
AD6JN
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KA4WJA
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Posts: 704




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« Reply #12 on: November 25, 2002, 02:27:42 PM »

Okay, I don't want to beat this horse further than necessary....But, I wish to express my disagreement with comments such as, "....probably cannot be solved."

This trouble probably CAN be solved.....
We still do not have the details of the situation, but assuming front-end overload is the primary cause, it may be as simple as moving (and/or elevating) the A99 antenna!

I have dealt with ham radio and "off-air" TV antennas for years.....and haven't found problems so severe that they couldn't be solved.....

{As a sidebar, my best friend uses his 60' tall TV tower as a support fora 40m delta loop, 30m sloper, 17m sloper, and a 2m antenna....and has a 80m horz loop, and a ground mounted HF vertical within 20' of this tower (smal city lot).....The only TVI he has expereinced is a "slight" amount on VHF hi-band, when operating 2m SSB with 150-200watts.....
Yes, he typically runs "barefoot" with 100watts output on HF....and....
Yes, most of these antennas are BELOW the TV antenna...but the 40m, 30m, and 17m antennas are within 5'-10' of the TV antenna/pre-amp, and the 2m antenna is on the same mast, out of the tower top....
The use of a "hi-quality" TV pre-amp and coax, as well as proper installation techniques makes a difference here also....}

So, my advice to Al is still the same:
Figure out what "type" of TVI you have, and use some of the recoomendations posted here to solve the problem.....
[There is NO need to subscribe to Cable, Nr to ask others in your home to cease watching TV when you're operating.....]

Good luck.
73,
John,   KA4WJA
 
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KD7KOY
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Posts: 97




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« Reply #13 on: November 30, 2002, 09:50:13 PM »

I've used a Imax 2000 and a A99 with good results..will even talk on 20 meters with a tuner.
No problem at all with TVI. As they said in previous psots, ground everything...Good Luck
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