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Author Topic: Need Coax Advice  (Read 4520 times)
AK4NX
Member

Posts: 17




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« on: November 24, 2011, 03:13:15 AM »

Hi guys,
Building my first station ever all HF, and this is my first attempt. I need to know which RG coax would be best for my needs.
Have an MFJ-1775 Dipole antenna which will be connected to a Yaesu FC902 Antenna Tuner a total coax run of 25 feet or less.
This will be connected to a Yaesu FT-902DM transmitter. Also have a Yaesu FRG-7700 reciever that I wish to use with an antenna
switch box.

What coax would be best in my situation. All replies and recommendations gratefully accepted by this newbie.
Thanks,
Jake
AK4NX
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W8JX
Member

Posts: 5640




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« Reply #1 on: November 24, 2011, 06:56:11 AM »

RG8x is totally fine here. No need for anything more. You could even use RG58 which is smaller yet and a bit easier to run/hide.
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AK4NX
Member

Posts: 17




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« Reply #2 on: November 24, 2011, 08:29:58 AM »

Thank you W8JX for the quick reply, and Happy Thanksgiving to you and your family.
I'll go with the RG8x.
John
AK4NX
73
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WB6BYU
Member

Posts: 13143




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« Reply #3 on: November 24, 2011, 12:43:51 PM »

I agree -  you should be operating the antenna at reasonably low SWR, and the feedline
is relatively short.  Losses will be low almost regardless of the feedline you choose.

RG-58 or RG-8X are both fine in this application.  RG-8X has lower losses (which will hardly
matter for that short length) and will be a bit more susceptible to crushing if it gets
stepped on or if you tighten a tie wrap too tight around it due to the foam insulator.
RG-58 is thinner with slightly higher loss, but is somewhat more resistant to being
crushed.

Or you can use the heavier, more expensive feedlines with even less loss.  But I doubt
you will notice any practical difference in everyday use.
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AK4NX
Member

Posts: 17




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« Reply #4 on: November 24, 2011, 01:57:43 PM »

Thank you WB6BYU for the reinforcement. I will order 25' RG8x tomorrow.
Happy Thanksgiving to you and yours.
John
AK4NX
73
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N5VTU
Member

Posts: 361




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« Reply #5 on: November 24, 2011, 07:49:57 PM »

John,

If the coax run is truly 25' or less, the RG-58 or RG-8x as already mentioned is fine at HF frequencies.  However, are you sure 25' is enough? That antenna will have to be located very low to the ground and near the transmitter for such a short run to work.  Normally shorter runs are more desirable, but you also want some height for the antenna and some separation from the operating position.  Since the MFJ-1775 is a rotatable dipole, you'll also need to allow some slack for the rotator loop, unless you plan on manually rotating it.  How do you plan on mounting the antenna? 

I'd recommend buying more coax than you think you need.  RG-58 and RG-8x are inexpensive.  If you have extra, use it on another project.

Stephen
N5VTU
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K9KJM
Member

Posts: 2416




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« Reply #6 on: November 24, 2011, 09:33:00 PM »

Belden RG 213 is considered the "Cadillac" of coax for HF use. Tough stuff that can be run over by a truck.
But as pointed out, Most anything will work just fine for such a short length at HF frequencies.

RG8X, etc would all be fine.  It is at VHF and UHF frequencies that low loss coax becomes important.

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AK4NX
Member

Posts: 17




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« Reply #7 on: November 25, 2011, 01:29:43 AM »

Hi Stephen,
I'm on the second deck (no one above me) of a beachside condo (no antennas allowed Roll Eyes ). My porch is 24' long by 14' wide and covered on the top; but open on three sides. The antenna will be suspended from the overhead and turned by hand when necessary. I have a clear shot to the East, North and South. Will probably have no difficulty with European transmissions. The distance measured from the antenna to the MFJ-4603 window pass through is only 16 feet, so 25 feet of the RG-8x will be more than adequate. My equipment is right on the other side of that window.
Thanks for the reply.
John
AK4NX
73

John,

If the coax run is truly 25' or less, the RG-58 or RG-8x as already mentioned is fine at HF frequencies.  However, are you sure 25' is enough? That antenna will have to be located very low to the ground and near the transmitter for such a short run to work.  Normally shorter runs are more desirable, but you also want some height for the antenna and some separation from the operating position.  Since the MFJ-1775 is a rotatable dipole, you'll also need to allow some slack for the rotator loop, unless you plan on manually rotating it.  How do you plan on mounting the antenna? 

I'd recommend buying more coax than you think you need.  RG-58 and RG-8x are inexpensive.  If you have extra, use it on another project.

Stephen
N5VTU
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AK4NX
Member

Posts: 17




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« Reply #8 on: November 25, 2011, 01:45:20 AM »

Hi K9KJM,
Thank you for that info, and I'll keep that in mind if my situation ever changes.....Never should have sold the house! Too many restrictions in these condos to suit me. Shocked
John
AK4NX
73

Belden RG 213 is considered the "Cadillac" of coax for HF use. Tough stuff that can be run over by a truck.
But as pointed out, Most anything will work just fine for such a short length at HF frequencies.

RG8X, etc would all be fine.  It is at VHF and UHF frequencies that low loss coax becomes important.


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W6RMK
Member

Posts: 650




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« Reply #9 on: November 25, 2011, 09:10:19 AM »

For that matter, low loss RG-6 type coax (75 ohm Cable TV coax) is cheap and would work well.  Probably lower loss than RG58 and about the same physical size.  foam dielectric for the most part, so don't crush it. 

Also handy because it's available EVERYWHERE if you need to add some or replace it.  It's available in other colors than black, so if visual inconspicuousness

Don't get hung up on the impedance issue.  You've got a tuner, your dipole isn't 50 ohms anyway, etc.

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W5LZ
Member

Posts: 477




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« Reply #10 on: November 26, 2011, 01:26:37 AM »

And then you come to the 'down side' of using RG-6 coax.  It uses aluminum for braid.  That means you are going to have lot'sa fun soldering it.
Your antenna probably isn't going to be 50 ohms, that's true.  But why add more complexity by using 75 ohm coax, cost?  There's just not that much difference in cost, you wouldn't be saving much.  For the distance involved, almost anything will work okay, even 'Rat-Shack' RG-58 (nasty thought, huh?).
 - Paul
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AK4NX
Member

Posts: 17




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« Reply #11 on: November 26, 2011, 05:44:00 AM »

Thanks for the reply and advice. Already pulled the trigger on the RG-8x and a MFJ-4603 window pass through (can't drilll holes in these walls).
John
AK4NX
73
 
For that matter, low loss RG-6 type coax (75 ohm Cable TV coax) is cheap and would work well.  Probably lower loss than RG58 and about the same physical size.  foam dielectric for the most part, so don't crush it. 

Also handy because it's available EVERYWHERE if you need to add some or replace it.  It's available in other colors than black, so if visual inconspicuousness

Don't get hung up on the impedance issue.  You've got a tuner, your dipole isn't 50 ohms anyway, etc.


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