Antenna in the Attic solution, help with parts and connectors

[pcradio]

I'm wanting to increase my TX and RX capability in simplex (radio to radio) communications when I'm not using a repeater and to help make my connection to my local repeater that much better. However, I will only be installing the antenna in the Attic. So, based on my research, I need one of the following antennas. I would appreciate opinions on which one and why.

Requirements:

• 30 foot run from attic to my office (lmr400?)
• Mobile unit with a SO-239 in.
• Handheld with a SMA Female in.

Which antenna?

• Copper J-Pole Antenna by KB9VBR
• Slim Jim Antenna by KB9VBR
• BR-6140 unity gain from Browning
• DBJ-UHF GMRS by Ed Fong

 

Thank your for your help.

[BoxCar]

If you have enough space, why not put in a base station antenna with some gain? There are several that don't require a ground plane as the have radials that are only a few inches in length. Your best bet would be to plan for the future and get a dual band if you want to take the ham Technician test. The ham 440 band is just below the FRS/GMRS band. 

[daschnoz]

LMR-400 is a must for UHF.  Look for DRF-400.  Same specs, 20% cheaper.  Try to use the fewest number of connections and adapters as possible.  Going from LMR-400 directly into an HT with an SMA connector will be akward.  Try to get that adapter cable with the needed male/female connectors with no gender benders or PL-259 to SMA adapters needed.  One end of the cable goes directly into the LMR-400, the other end goes directly into the radio.

You won't go wrong with the Ed Fong antenna.  Remember that you need to wrap it in 200psi grade PVC pipe.  They are tuned for that and results without the pipe may be different. 

The BR-6157 (different than your proposed) has 4.5dBd of gain, which equates to a gain facor of 2.8... meaning that 5 watts of input power radiates as if you put 14 watts into a unity gain antenna.  Antenna gain also works on receive to boost the incoming signal by the same amount.  It is 32-1/2" tall (I don't know if that's a problem for you).

 

ETA:

Boxcar posted while I was typing. +1 on looking into a dual band antenna.  GMRS is the gateway drug to a HAM ticket.

[oneeyeross]

I have two J-poles from KB9VBR, one for 2 meter and one for GMRS.  I like his work, the antennae do what they are s'posed to do, and the price is reasonable.  I also have a roll-up slim Jim I use for a HT that does duty as a LEO scanner.  

The J-pole does a better job (at 2 meter) than the Slim Jim (close to 2 meter police bands), but that might also be the difference between a good 2 meter rig and cheap Chinese hand held....but for the money, I would say that J-pole will probably last longer.

Honestly, can't go wrong with either option in my opinion.

[pcradio]

I went with the Copper J-Pole Antenna by KB9VBR. Decided to mount it on the roof as well and run a grounding wire, from a ground clamp, down to a grounding rod. Went with N female connector and 30ft of LMR-400 equivalent cable. Still getting everything connected. Will report success when done.

[pcradio]

I have tested with the antenna on the roof, as well as in the Attic. In my testing it seems identical. So, I will be keeping it in the attic. For now, the extra expense of getting it right when on the roof was not worth it to me. To significantly increase range, I would have to raise the antenna a lot higher than what my roof could provide.

[daschnoz]

[WROA675]

On 8/26/2021 at 4:27 PM, BoxCar said:

If you have enough space, why not put in a base station antenna with some gain?

Do j-pole antennas not have any gain to them, by design? (I'm getting one to try for better range/performance for my location and stay under the HOA radar).

If no gain, is there a way to modify it for gain, or at least to not have any loss in tx/rx?

[AdmiralCochrane]

A good J pole should have about 3db gain.  There are variations with a little more gain, but I am not fully versed in them. 

I have successfully made and used 3 J-poles and am currently using one on my 1.25m Alinco. My nanonva and wattmeter both say the SWR is in the 1.1:1 range, where my Comet triband antenna is about 1.5:1 on 1.25m

[AdmiralCochrane]

And discount what you will hear about the Slim Jim variant.  It has been debunked, it has no more gain than a plain J-pole.  The myth of the Slim Jim goes back to an early article about the design that "hopes" to have higher gain.  No such improvement was ever detected, but the legend goes on via "Post Office" game repetition of the original story with the details left out. 

[maddogrecurve]

On 11/9/2021 at 10:28 AM, Papatree said:

Do j-pole antennas not have any gain to them, by design? (I'm getting one to try for better range/performance for my location and stay under the HOA radar).

If no gain, is there a way to modify it for gain, or at least to not have any loss in tx/rx?

J-Poles do have gain!  Not a bunch, but they work much better than dipoles!  They outperform many commercial loaded antennas as well!  Look up the info on the net, but be careful, some people are biased in both directions, so make sure that you are using a discerning eye!

[PACNWComms]

Have heard for years the comments about J-pole antennas working better than.....insert some other type.....but then find out it is just someones opinion as well. In ten years of providing emergency communications services to the oil industry, hurricanes Katrina, Wilma, Rita, oil spills, forest fires, and floods, many sites ended up buying or making J-pole antennas for their offices, with many being in attics and upper offices. However, in many cases Laird, Antennex, Cushcraft, and many other antennas worked just as well, provided they had a good ground plane, and were not placed in attics with metal roofs. The metal roof aspect happened several times, as many commercial buildings use them for ease of maintenance and durability. Some sites also used VHF, with everything from Shakespeare fiberglass antennas and Morad based loaded antennas being used. Reception and transmission also involve a lot of variable, and the attention to detail on installation, coax, connectors (no adapters), ground plane, length of coax, other electrical items that may interfere. The antenna is still one of the most important aspects of a radio system. Glad the J-pole worked for your use case.

[BoxCar]

16 hours ago, PACNWComms said:

Have heard for years the comments about J-pole antennas working better than.....insert some other type.....but then find out it is just someones opinion as well. In ten years of providing emergency communications services to the oil industry, hurricanes Katrina, Wilma, Rita, oil spills, forest fires, and floods, many sites ended up buying or making J-pole antennas for their offices, with many being in attics and upper offices. However, in many cases Laird, Antennex, Cushcraft, and many other antennas worked just as well, provided they had a good ground plane, and were not placed in attics with metal roofs. The metal roof aspect happened several times, as many commercial buildings use them for ease of maintenance and durability. Some sites also used VHF, with everything from Shakespeare fiberglass antennas and Morad based loaded antennas being used. Reception and transmission also involve a lot of variable, and the attention to detail on installation, coax, connectors (no adapters), ground plane, length of coax, other electrical items that may interfere. The antenna is still one of the most important aspects of a radio system. Glad the J-pole worked for your use case.

The key difference between using a J-pole and another antenna is the installation. J-poles don't need a ground plane as it is part of the antenna design. A vertical often requires a ground plane and/or radials to perform as intended, I have both a J-pole and a vertical whip I use for 2M/70cm. The whip is a mag mount and gets the better signal reports but that I feel is due to the installation. Both, when either is used, are at roughly the same height but the vertical is on a sheet of steel measuring 2 feet on a side as its ccounterpoise.