Call Search
     

New to Ham Radio?
My Profile

Community
Articles
Forums
News
Reviews
Friends Remembered
Strays
Survey Question

Operating
Contesting
DX Cluster Spots
Propagation

Resources
Calendar
Classifieds
Ham Exams
Ham Links
List Archives
News Articles
Product Reviews
QSL Managers

Site Info
eHam Help (FAQ)
Support the site
The eHam Team
Advertising Info
Vision Statement
About eHam.net

   Home   Help Search  
Pages: [1] 2 Next   Go Down
  Print  
Author Topic: Coax for feed line 2m/70cm  (Read 4652 times)
K5UNX
Member

Posts: 247


WWW

Ignore
« on: February 24, 2012, 06:44:47 PM »

Hi all, I have been surfing the web for hours and found nothing but confusing info. I know little about this stuff as I am new . . . I have had my license  for a long time but have been dormant as far as radio goes.

I have a Yaseu FT60R so far. I would like to put up a dual band antenna. I was thinking about building a copper pipe j-pole but am now considering a Arrow Open Stub J-Pole . Since I don't have soldering equipment yet, it would be cheaper to buy the Arrow at this point.

I think I have three reasonable choices for mounting it. 1) Vent pipe on the roof. 2) Attach to side of roof overhang on some sort of small pole. There is nice heavy wood up there to screw into. 3) Hang from roof joists in the attic. There is not much in the attic as far as ducting, wiring etc. It's pretty open up there and I could hang a 6ft tall or less antenna pretty easily.

On a vent pipe or attached to the side of the house, I think I'll need about 60 ft of coax for a feed line. If I hang it in the attic, I think I can get by with maybe 25 ft. I think I'll need a small flexible pigtail for the direct attach to the HT. Sometime this spring, I'll be getting a dual band mobile unit that I'll set up in some sort of "go-box" with a DC power supply. It will be my "base" dual band as well as my pick up and go kit for volunteer events etc.

I know RG-58 and RG-8X would work but I have read they are higher loss that it sounds like I need.

What type coax do I need???

Wayne - K5UNX

Logged

W8JX
Member

Posts: 5664




Ignore
« Reply #1 on: February 24, 2012, 07:00:17 PM »

Well I would not really use RG8x for 70cm on a 60 foot run not 58 for sure. RG-213 will work here. It run is longer use 9913 or LMR 400. I know building a antenna can be fun but i would also suggest a commercial made dual band vertical with 8 or more db gain on 440 and height and antenna gain is very important on 440
Logged

--------------------------------------
All posted wireless using Win 8.1 RT, a Android tablet using 4G/LTE/WiFi or Sprint Note 3.
K5UNX
Member

Posts: 247


WWW

Ignore
« Reply #2 on: February 24, 2012, 07:34:08 PM »

I can't find a gain rating for the Arrow . . . I did find the Diamond X50A and it's close to 8db gain on 440. Better? I don't want to get too expensive. $100 or less would be nice at this point for the antenna alone.
Logged

W8JX
Member

Posts: 5664




Ignore
« Reply #3 on: February 24, 2012, 08:21:02 PM »

I can't find a gain rating for the Arrow . . . I did find the Diamond X50A and it's close to 8db gain on 440. Better? I don't want to get too expensive. $100 or less would be nice at this point for the antenna alone.

I have had a X50 Diamond clone up for 15 years and have been very pleased with it. It is only up 25 feet at base as a low profile backup antenna as a have a 2m only Hustler G7 antenna up 50 feet at base. I have been feeding it with about 75 feet RG213 since I put it up too.
Logged

--------------------------------------
All posted wireless using Win 8.1 RT, a Android tablet using 4G/LTE/WiFi or Sprint Note 3.
N4CR
Member

Posts: 1662




Ignore
« Reply #4 on: February 24, 2012, 09:00:34 PM »

If you have $100 to spend, build a 1/4 wave ground plane antenna for $10 and use the other $90 on better coax and getting it up higher. Antenna gain is no substitute for height at these frequencies.

http://www.hamuniverse.com/2metergp.html

http://www.hamuniverse.com/na4it2440groundplane.html

If you don't have the common tools to make one of these, lean on the hams in your area. They have everything it takes to make one of these in their junk drawers and toolboxes. It may not look like much, but it's all it takes to get on the air in fine fashion. And later when you replace it with a commercial one, you don't take much of a loss. Copper pipe is expensive.

A 1/4 wave ground plane has exactly the same gain as a J-Pole without any of the drawbacks of the J-Pole which can be notoriously difficult to get into the air and not have it couple into the metal around it (even the coax shield). This can make it's pattern close to useless in some directions. Not what you really want from an omni directional design.

The feed point of the half wave portion of a J-Pole is high impedance (high voltage, not high current) this makes them tricky to isolate. The feed point of a 1/4 wave ground plane is low impedance (high current, not voltage) and this makes it much easier to isolate from the surroundings.

Put all of your money into getting the antenna up higher. That's the holy grail of VHF and UHF communications.

I like LMR-400 for coax on UHF but it's pricey.
« Last Edit: February 24, 2012, 09:02:47 PM by N4CR » Logged

73 de N4CR, Phil

We are Coulomb of Borg. Resistance is futile. Voltage, on the other hand, has potential.
KA4POL
Member

Posts: 1967




Ignore
« Reply #5 on: February 25, 2012, 12:13:35 AM »

My choice is Aircell 5 which has very low attenuation and the outside is UV resistant. You did not mention where you are located. There may be much sunshine.
As far as the antenna is concerned take the wind load into account. Is the vent pipe strong enough for that? You may be better off setting up a mast from the attic through the roof.
What will you be doing in the future? If you consider VHF/UHF SSB you may also think about an antenna suited for that. A good antenna is the best amplifier.
Logged
W8JX
Member

Posts: 5664




Ignore
« Reply #6 on: February 25, 2012, 05:13:30 AM »

If you have $100 to spend, build a 1/4 wave ground plane antenna for $10 and use the other $90 on better coax and getting it up higher. Antenna gain is no substitute for height at these frequencies.

I strongly disagree because the is a phenomenon in VHF and UHF known as capture area and the larger the antenna the better to deal with this. There tends to be small holes in coverage that can easily be seen at times when you move a foot or two side to side or up or down with HT in a weak signal area. A large/longer vertical spans these "holes" better and will give consistent coverage. It also lowers radiation angle and boosts ERP.

It is better to spend more on antenna and less on coax because it does no good to use high dollar coax on little more than a dummy load antenna that does not radiate or hear well.
Logged

--------------------------------------
All posted wireless using Win 8.1 RT, a Android tablet using 4G/LTE/WiFi or Sprint Note 3.
K5UNX
Member

Posts: 247


WWW

Ignore
« Reply #7 on: February 25, 2012, 08:12:03 AM »

I don't think height is a real issue. I live on top of a large hill. I can reach the club repeater 20 miles away nicely with my ribber ducky on the HT from inside the house. Dummy me had a GP antenna that a guy made me. It was in the shed and I threw it out 2 years ago . . . this last year I decided to get back into Ham Radio . . . Go figure!

« Last Edit: February 25, 2012, 04:04:46 PM by K5UNX » Logged

N4CR
Member

Posts: 1662




Ignore
« Reply #8 on: February 25, 2012, 03:14:16 PM »

If you have $100 to spend, build a 1/4 wave ground plane antenna for $10 and use the other $90 on better coax and getting it up higher. Antenna gain is no substitute for height at these frequencies.

I strongly disagree because the is a phenomenon in VHF and UHF known as capture area and the larger the antenna the better to deal with this

A J-Pole has the same capture area as a 1/4 wave ground plane. He was going to build a J-Pole. I suggested a less expensive better behaved antenna that has essentially identical specs.

Antenna gain is no substitute for height. Now he includes more info. He's on the top of a hill. In that case he's all ready in the best possible situation and gain won't mean much.

Put up a hand made quarter wave ground plane and see if you get the repeaters you want to get. If it works, you are done with almost no money out of your pocket. No way would I spend a dime on a J-Pole. A home brew 1/4 wave ground plane is an inexpensive experiment with almost no downside. It even has less weight and less wind load than a J-Pole.

You can get a little better antenna by spending a lot of money on a commercially built gain antenna. I've had expensive gain antennas up here at my house and right now I'm running on a 1/4 wave ground plane built in about 20 minutes. I can't tell the difference when I'm sitting at the radio. I still hit all the same repeaters with the same signal as I did before.
Logged

73 de N4CR, Phil

We are Coulomb of Borg. Resistance is futile. Voltage, on the other hand, has potential.
K5UNX
Member

Posts: 247


WWW

Ignore
« Reply #9 on: February 25, 2012, 04:05:41 PM »

My previous post, I meant 20 miles not 2 . . . I repaired that post. Sorry for the confusion. Looking at the map to confirm that distance, it's closer to 15 than 20.

« Last Edit: February 25, 2012, 04:08:42 PM by K5UNX » Logged

KB1GMX
Member

Posts: 761




Ignore
« Reply #10 on: February 25, 2012, 05:44:13 PM »

Ok things I have read...

Aircell-5 is the same as Times LMR-195 (same size and dual foil/braid)and not my
first choice for anything more than short jumpers or less than 16ft runs.

The cable to use, LMR400, Buryflex or Belden 9914 are better, then we have
RG213 and way behind LMR240 and RG8x.  I listed them by price where
LMR400 is the price king and Buryflex is a good deal.  RG213, use the best
non contaminating version as it's good stuff just not as low loss. 

Arrow 146/440 dual band Jpole it's unity gain compared to a vertical dipole and slightly
better than a 1/4wave vertical.  It's upside is rugged and hard to mess up and has a fairly
low profile.  I use up as my FM repeater antenna with excellent results out to 60+ miles.

A better choice is a gain vertical in the 6db class for both bands.  The advantage is you
make up for coax loss and make good use of your power on the horizon.

Like at least one person said, spend your money of the coax, and don't scrimp on
the antenna.

Also 20 miles is not far out, though for some repeaters with poor location or other issues
that may be their limit.  Least that the case here(New England), in flatter country it's less
a problem.

Allison

Logged
N4CR
Member

Posts: 1662




Ignore
« Reply #11 on: February 25, 2012, 06:09:21 PM »

Well, Arrow can call it a J-pole, but it's got a quarter wave driven element on 2 meters and a 3/4 wave driven element on 440. Marketing may have called it a j-pole but it isn't.

Show me the shorted quarter wave stub feeding the half wave radiator (the classic end fed zep) and I'll believe it's a j-pole.
Logged

73 de N4CR, Phil

We are Coulomb of Borg. Resistance is futile. Voltage, on the other hand, has potential.
K2FOX
Member

Posts: 106




Ignore
« Reply #12 on: February 25, 2012, 06:39:00 PM »

I use Andrew 3/8 inch heliax for all antennas (HF/VHF/UHF), right up to the rotors, then switch over to Flexi 9913. Two of these runs are well over 100 feet. Very low SWR!!  Check Ebay, 50 feet for $44.99, free shipping!!!

http://www.ebay.com/itm/Andrew-Heliax-F2A-PNMNR-50-FSJ2-50-SureFlex-Coax-Cable-/200619591016?pt=LH_DefaultDomain_0&hash=item2eb5dc0568

Logged
KD4LLA
Member

Posts: 454




Ignore
« Reply #13 on: February 25, 2012, 09:10:07 PM »

If you have $100 to spend, build a 1/4 wave ground plane antenna for $10 and use the other $90 on better coax and getting it up higher. Antenna gain is no substitute for height at these frequencies.

Exactly!  Most gain figures on a VHF/UHF vertical is the manufacturer's dream...

Mike
Logged
W8JX
Member

Posts: 5664




Ignore
« Reply #14 on: February 25, 2012, 09:32:59 PM »

If you have $100 to spend, build a 1/4 wave ground plane antenna for $10 and use the other $90 on better coax and getting it up higher. Antenna gain is no substitute for height at these frequencies.

Exactly!  Most gain figures on a VHF/UHF vertical is the manufacturer's dream...

Mike

Not at all. The dream is than the a 1/4 wave works as well as colinear or even a 5/8 wave. Money is far better spent on antenna than coax here. This is not HF
Logged

--------------------------------------
All posted wireless using Win 8.1 RT, a Android tablet using 4G/LTE/WiFi or Sprint Note 3.
Pages: [1] 2 Next   Go Up
  Print  
 
Jump to:  

Powered by MySQL Powered by PHP Powered by SMF 1.1.11 | SMF © 2006-2009, Simple Machines LLC Valid XHTML 1.0! Valid CSS!