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RG58 to RG6

Jun 22nd 2013, 15:49

Ham1Stuff

Joined: May 23rd 2013, 20:08
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My house was prewired for cable and satellite TV using RG6 cable. There is a conduit in the wall from the roof to a box in the garage. From that box there are pairs of RG6 cables running to eight locations in the house. One those locations is my "office" where I would like to set up my "shack". If I used a MFJ -1788 antenna on the roof and ran RG58 to the box in the garage, could I connect the RG58 to the RG6 to carry signal to the (would be) shack?
Jun 22nd 2013, 20:35

KB0HAE

Joined: Apr 4th 1998, 00:00
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Hi. While the MFJ 1788 gets some good and some not so good reviews, it is obviously meant for those with extreme limitations on what they can put up for antennas. As for what you want to do with the coax, I would not recommend it. RG6 cable is 75 ohm coax, where your radio will be looking for 50 ohm coax. Therefore you will not ever get better than 1.5:1 SWR. and that is only if the antenna is tuned for 1:1 SWR. The antenna also will be looking for 50 ohm coax, and may not tune properly with 75 ohn RG6. Also, there may not be a single run of coax to the roof, it may have one or more splitters installed somewhere.

I would not use RG58. Get some decent RG8x, RG8, or something better if you need a long run to your antenna. and in my not so humble opinion there are probably better HF antennas than the MFJ1788 unless you are extremely restricted in what you can put up for an antenna.
Jun 22nd 2013, 21:37

Ham1Stuff

Joined: May 23rd 2013, 20:08
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Thanks for the info. I'll scratch "Plan A". Would a workable "Plan B" be to set up my shack in the garage by running RG8x or RG8 from a roof mounted antenna down the conduit to the box and "sneak" out under the cover of the box to the rig? Currently there are 3 DishTV runs of coax through the conduit and continuing to the 3 Dish receivers we have in the house. There would be no spliter on the ham coax. Would there be reactance with the the dish cables? We live in an HMO environment which limits what we can put up as an antenna. Can you recommend an alternative to the MFJ 1788?
Jun 22nd 2013, 21:39

Ham1Stuff

Joined: May 23rd 2013, 20:08
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Ooops! HMO is spelled HOA!
Jun 23rd 2013, 03:44

AA6E

Joined: Apr 4th 1998, 00:00
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Running your coax together with satellite TV cables is asking for trouble. There is likely to be some coupling, quite possibly enough to screw up your TV systems, especially if your antenna is not completely balanced. (I.e. some current runs on the outside of your coax.) It also depends on your power level. If you're QRP, you can be more relaxed!

High-Q small loops can work, but they can be lossy and tricky to tune and couple to. A 1/2 wave dipole is one of the best choices if you have the space. For restricted spaces, you could also look at mobile-style antennas - loaded whips of one sort or another. Or trap verticals.

Zack W1VT will tell you that you can always make a flagpole antenna. Flag poles are "protected", meaning that HOAs can't stop you from putting one up. If it just happens to be an antenna, too, well...

73 & good luck

Martin AA6E
Jun 23rd 2013, 04:06

W0BTU

Joined: Apr 4th 1998, 00:00
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There is nothing sacred about 50 ohm coax. I, and many other hams, use 75 ohm CATV cable for almost everything. I have over 1000 feet of flooded RG-6 (F-6) cable running to my transmitting and receiving antennas. I've also used discarded 1/2 and 3/4" hardline for weak-signal DXing on 144 MHz. No problems and no worries.

http://forums.qrz.com/showthread.php?279520-RG-6-vs-RG-58
http://vk1od.net/transmissionline/RG6/

73, Mike
www.w0btu.com
Jun 23rd 2013, 17:50

KB0HAE

Joined: Apr 4th 1998, 00:00
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Total Posts: 0
Hi. The original post was talking about connecting RG58 to RG6. RG58 is relatively lossy even at HF frequencies, and there would be a mismatch between it and the RG6, causing more loss.

While some hams use RG6 and 75 ohm hardline sucessfully, there will always be a mismatch between the 75 ohm coax and the 50 ohm output of the radio. This may be acceptable in some circumstances, but not in others. A 1.5:1 VSWR is not that bad, but if your antenna does not have a 1:1 VSWR at the operating frequency, it could be a problem.

While VSWR is not the only factor determining the effiency of an antenna system, it cannot be discounted. Even my 25+ years old Kenwood TS-430Ss will cut power back when transmitting into an antenna system with a high VSWR. The reflected power can cause heat in transmission lines and the tranceiver's final amp stages.

AA6E also made some valid points. If Ham1stuff was to run RG6 from his shack to the antenna, but away from the satellite coax, it could work. RG6 is a low loss coax compaired to RG58. A lot depends on the exact situation, which is not known at this point as Ham1stuff has not put up any antenna yet, or even bought one.
Jun 23rd 2013, 18:45

W0BTU

Joined: Apr 4th 1998, 00:00
Total Topics: 0
Total Posts: 0
Quote by KB0HAE
Hi. The original post was talking about connecting RG58 to RG6. ... there would be a mismatch ...


Yes there would. I misread that as RG59 to RG6. Should have paid closer attention. :-)

73, Mike
www.w0btu.com

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