| Author |
Message |
    
Roninboricua
Junior Member
Username: Roninboricua
Post Number: 24
Registered: 1-2006
| | Posted on Friday, February 17, 2006 - 3:05 pm: | 
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Some people say the rg8x is better for tvi because its 97% Copper Shield and 3000 Watt Power Handling. That is what im using right now, and there's no tvi till I go over 200 watts, the thing is I have alot more than 200 watts.
So I went ahead and bought the LMR400 but haven't installed it cause I don't feel like taking the antenna down twice just cause the LMR400 didn't work. I know there's alot more factors that can contribute to TVI, but I just want to know about the coax.
How many watts can the LMR400 handle and is it better for TVI? |
Hotwire
Advanced Member
Username: Hotwire
Post Number: 939
Registered: 1-2005
| | Posted on Saturday, February 18, 2006 - 3:13 pm: |
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LMR400 is way better than mini8. I have the same problem using mini8. Over 200 watts starts tvi. 500 watts will shut the nieghbors tv off! I'm going to upgrade my coax when the weather warms up to at least rg213. Should cure my tvi problems. Its worth taking the antenna down to upgrade to LMR400, I would do it. You will be amazed at the reciever improvment not to mention the transmitter. Mini8 is basically capable of handling around a kilowatt and LMR400 I think is capable of 2 kilowatts. |
Patzerozero
Senior Member
Username: Patzerozero
Post Number: 2441
Registered: 7-2004
| | Posted on Saturday, February 18, 2006 - 7:01 pm: |
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real 9913 has a SLIGHLTY better braid coverage, & i believe lmr400 uses copper-clad aluminum center conductor vs copper for 9913. though probably not enough more to see a difference.
upgrade to 9913 in my mobile eliminated 99% of RFI to truck. higher velocity factor of 9913(and lmr400) vs 213 allows coax to be longer at 1/2 wavelength.
have put 2kw through GOOD double shield rg8x with no trouble. astatic 3k antenna was not happy at 1kw though  |
Dale
Intermediate Member
Username: Dale
Post Number: 322
Registered: 12-2002
| | Posted on Sunday, February 19, 2006 - 8:35 am: |
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idput up lmr coax on my setup id do it again
cant gareentee will cure tvi problems cause tvi
isnt caused by coax usualy caused by not grounding antenna or over tuned radios,clipped radios,ect. i will say this lmr has very low loss meaning more of yor signal getting 2 antenna.also lmr is double shielded coax.when ya
take it down ground your antenna with #6 BARE COPPER WIRE. and a 9 ft grounding rod this should help with tvi but probaly wont cure it |
Patzerozero
Senior Member
Username: Patzerozero
Post Number: 2446
Registered: 7-2004
| | Posted on Sunday, February 19, 2006 - 11:29 am: |
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check out www.ocarc.ca/coax.htm for their
'Online Coax Cable Loss / Antenna Gain Calculator'
you will see the following:
65' run length at 27 mHz with a 1.1:1 swr & 30 watts AM carrier input, you will get the following results with these 3 coaxes:
9913 coax---rg213 coax---lmr400 coax
0.419-------0.679--------0.411 db loss(cable)
0.002-------0.003--------0.002 db swr loss
0.42--------0.612--------0.413 db total loss
27.233------25.64--------27.279 watts output
SO, you lose 46/1000ths of a watt (with 30 watts dead key) cheapening out by using the 9913 i use vs lmr400. 413/1000ths-almost one half of 1 watt-(with 30 watts input) by really cheapening out & using rg213. using rg58(skinny cheap stuff) looses 5 more watts. really adds up, huh
if you check belden's site, it explains the cause & effect of different shield percentages & foil over braid. yes, for rfi purposes, both rvc & xmit, always go with highest percentage available & extra foil, there are benefits. |
Tech833
Moderator
Username: Tech833
Post Number: 1220
Registered: 8-2002
| | Posted on Sunday, February 19, 2006 - 1:24 pm: |
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Since LMR-400 has 100% shielding and you say RG8X has only 97% shielding (I read somewhere it was more like 85%), then obviously, the better shielded coax will eliminate any RF feedline radiation TVI that may exist. It will NOT cure TVI if it is coming from your antenna! Assuming you are using a working low-pass filter with at least 60 dB of rolloff and your system is properly grounded, you should not cause any harmonic TVI. |
Patzerozero
Senior Member
Username: Patzerozero
Post Number: 2448
Registered: 7-2004
| | Posted on Sunday, February 19, 2006 - 2:46 pm: |
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9913 also has 100% shield by way of foil. there are several grades of 8x, including a couple double shielded as well, & range from 65%(YIKES!) to 100%, though braid coverage on at least 1 of those with foil is only 90% per specs.
i have a no-name tv the kids play video games on. 4 watts-150 watts, AM, SSB, CB, 6 meters, makes no difference. nor does using my maco v5/8 with 9913, or a 'no ground plane' 30 inch glas antenna with rg58. the volume of 'my' audio overlaoding speakers is the same in any combination, but there is no affect on the picture. full power from my mobile in the driveway makes the kids stand up & take notice, though-i can shut the game off from the driveway |
Hollowpoint445
Senior Member
Username: Hollowpoint445
Post Number: 1096
Registered: 6-2004
| | Posted on Sunday, February 19, 2006 - 5:35 pm: |
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TVI is a harmonic problem that causes inteference on channels 2 and 6 and some others if it's really bad. It's easily cured with a low pass filter.
If you have no problems until you reach a certain power level you are not having a TVI problem, it's an RFI problem caused by a strong RF field.
Coax with better shielding is a good idea, but it probably won't help much. Your problem is most likely caused because your antenna is not high enough or there is RF coming back down the feedline. Either raise the antenna or roll some coax into a choke as close to the antenna feed point as possible. Radials or ferrite beads can also help. |
Dale
Intermediate Member
Username: Dale
Post Number: 324
Registered: 12-2002
| | Posted on Sunday, February 19, 2006 - 7:06 pm: |
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lmr is 100 percent shielded actually double shielded imho making it the best |
Patzerozero
Senior Member
Username: Patzerozero
Post Number: 2458
Registered: 7-2004
| | Posted on Sunday, February 19, 2006 - 8:54 pm: |
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lmr as well as 9913 have a foil shield, in essence both are 100%. lmr has 91% braid coverage, 9913 has 95% braid coverage. with the same length of both, the lmr has 8/1000ths of a db less loss then 9913. aside from the fact the ear can't notice the difference, is that even a truly measurable difference???
as for not allowing rf to enter or exit the cable, before the antenna, if the connectors are properly installed, 9913 should be the better choice for rfi reduction.
lastly, if the neighbor says you come over his tv EVERY time he has it on, he watches too much tv |
Dale
Intermediate Member
Username: Dale
Post Number: 327
Registered: 12-2002
| | Posted on Monday, February 20, 2006 - 7:17 pm: |
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i agree with neighbor watching too much tv |
Road_warrior
Senior Member
Username: Road_warrior
Post Number: 1248
Registered: 7-2004
| | Posted on Tuesday, February 21, 2006 - 8:57 am: |
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Low pass filters work best on TVs using Antennas.
The correct Common Mode chokes works better
on cable Tv. Or Cable could have some leakage. |
Roninboricua
Junior Member
Username: Roninboricua
Post Number: 25
Registered: 1-2006
| | Posted on Tuesday, February 21, 2006 - 2:57 pm: |
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I installed the LMR400, and for some reason my swr went up alittle. It used to be 1.0, Now i have about 1.5 on 11 meters. 12 meters is about 1.7. I have a rat shack swr meter, not the most acurate i've heard.
I hookep up about 10 ferrite snap on chockes one right after the other on the bottom of the feedpoint on my v/58.
But tvi is still present in my house. When i use the palomar300 there's no problems. But when i hook up the x600, even at the lowest setting, that's about 100 dead key 450pep. I was even getting in the radio.
The antenna is only about 5 feet from the satelite dish. It goes up 10 above the house. The house is about 20 tall.
But with the palomar I have no problems. So I kinda ruled out that factor.
Why would my swr go up? Is it the x600 causing the tvi? |
1861
Intermediate Member
Username: 1861
Post Number: 455
Registered: 2-2004
| | Posted on Tuesday, February 21, 2006 - 4:10 pm: |
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THE X 600 IS PROBABLY JUST CAUSING OVERLOAD . MY MAVERICK 250 DOES THE SAME - DK 150 SWING ABOUT 600 . MY TEXAS STAR 250 DOESN,T . |
Kmt36264
Junior Member
Username: Kmt36264
Post Number: 18
Registered: 1-2006
| | Posted on Tuesday, February 21, 2006 - 8:41 pm: |
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Better coax will show higher SWR because less loss also applies to the reflected power. All of the standing wave doesn't make it back to the swr meter with a more lossy cable.
A few things to think about while working on the TVI (worked for me!):
1. Make sure the coax shield is soldered to the connectors. If a connector will begin to turn and unscrew, it is probably not soldered well.
2. Don't put the radio above the ground floor.
3. Move the ferrites from the cb antenna to the TV power cord and satellite coax. Wrap it through as many times as possible. If you are having front-end-overload, this can help.
4. Ground the antenna pole with a copper clad rod. If there are joints in the tower/pole that would cause resistance, run #4 solid all the way up to the antenna.
5. Add a ground to the radio, amp, meters, and anything that is inside and part of the CB system, and attach to a copper clad ground rod. The ground bus from the back of the radio to the ground rod should be less than 1/4 wavelength.
6. Wind an air core choke near the antenna rather than using beads.
7. Check the grounds on the satellite system. There is usually one where the cables enter the house. You might try adding another at the dish.
8. Clean and tighten up your AC ground at the service entrance.
9. Solder connections whenever possible and use ox-guard when clamping ground connections.
10. Search the net for articles on RFI and TVI. There is lots of good reading out there. |
Road_warrior
Senior Member
Username: Road_warrior
Post Number: 1251
Registered: 7-2004
| | Posted on Wednesday, February 22, 2006 - 2:36 pm: |
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Also check for poor coax on the dish or
poorly shielded patch cords between the satellite
reciever and Tv reciever. VCR can often increase
chances of interference.
Check for: poor grounding on the dish and
loose connections.
Keep patch cords as short as possible.
Interference could also enter the satellite reciever through the AC Line. |
