[AK-VHF] AK-VHF Net: 29 Jan - 146.52 FM

[Brandon Clark]

Yep, definitely had the picture (map?) rotated a bit in my mind.

J pole antennas have a lot of advantages: not too large, vertical polarization, a little bit of gain, easy coax routing out the bottom, and no need for a ground plane. My first 2 meter antenna was a copper plumbing pipe j pole that I built. I initially had the coax center and shield connected to the metal with hose clamps, but later on soldered one of those flange connectors you mentioned as a replacement. With the 1/2" diameter tubing the < 1.5:1 SWR bandwidth covers the whole 2 M band.

I didn't use that antenna much over the last few years, but recently put it back into service again as my POTA VHF antenna. It works great when I'm activating from my truck; I used some leftover fiberglass box tubing scraps (McMaster Carr) to make an insulated mount that connects the antenna to the cross bars on my camper shell. Clean, simple, sturdy. That antenna is a bit long and cumbersome to carry into the backcountry though.

What I've been using for backpack-portable work is a fan dipole utilizing bronze brazing rods for the elements, connected to a simple center insulator I made from some leftover plastic and machine screws. Ring terminals soldered onto the brazing rods make for easy connection to the center insulator using wing nuts on the machine screws. With brazing rod element pairs for both 2 M and 70 cm I get a nice clean pattern on both bands. A collapsible tent pole makes for a backpack portable mast.

The only drawback is that the antenna and tent pole are a little bulky on a backpack even when collapsed and disassembled. I'm thinking to do the same general idea, but utilize the leftover window line to make the elements, and only bring the tent pole when I don't have another means of support (tree, another antenna, etc.). With the ladder line I can cut the sides for different band combinations and bring whatever I want to run: 2 M, 6 M, 70 cm, or other bands. In a pinch it could even serve as a backup HF antenna (with some other longer scrounged wire and my tuner).

Brandon Clark, KL7BSC
https://brandonclarklabs.com/

Sent with [ProtonMail](https://protonmail.com/) Secure Email.

‐‐‐‐‐‐‐ Original Message ‐‐‐‐‐‐‐

On Tuesday, February 1st, 2022 at 11:25, Ed Cole kl7uw at acsalaska.net wrote:

> Brandon,
>
> OK, then wrong picture in head?
>
> I had a 80/40m alligator clip dipole for use on the Iditarod (even
>
> called Iditarod Special). Was simple, pretuned, roll-up portable.
>
> My 80/40m inverted-V is fan-style. But I found 40m to be very narrow
>
> band probably due to influence of the 80m wires. Better to spread each
>
> band out horizontal several feet. problem for portable is having end
>
> supports for the antenna.
>
> When I rebuild my dipole 40m wires will be 90 degrees from 80m wires and
>
> be fed with open wire from ground where my 1:1 balun will connect for
>
> 80/40m. I will short the open wire and connect a base coil for loading
>
> as a loaded vertical on 630 or 160m. Of course not a portable antenna.
>
> Instead of twin lead j-pole consider a metal tubing j-pole. Can be made
>
> from 1/8 or 1/4 brass tubing and soldered with coax flange connector to
>
> attach coax to. Have a 2-inch mailing tube or maybe pvc pipe with caps
>
> for carrying.
>
> I even made a J-pole using TV-mast as main part and adding a 1/4 wave
>
> stub of 1/2 inch copper to the side 1/2 wave below the top. Just
>
> connected coax at bottom of stub and mast at the same point (stub
>
> insulated from mast). That was my first 2m antenna when I lived in
>
> Hope. Worked 94 repeater FB.
>
> 73, Ed
>
> On 2/1/2022 10:01 AM, Brandon Clark via ak-vhf wrote:
>
>> Hi Ed,
>>
>> The funny part is that I can't even use the "I didn't have a compass" excuse. I always bring one, but I didn't use it in locating my preferred campsite since I knew I was at the right lake, so had a good picture of things in my head . . . or so I thought, lol.
>>
>> The kind of linked dipole you mention (with the alligator clips) work great. One of those cut for 40 M and 20 M used to be my go-to antenna for summits on the air back in Ca. With a telescoping fiberglass mast from MFJ as a support it worked great.
>>
>> The j pole that I built (which had the problem) was one of the "DBJ-2" designs that are really popular. It is made from twin lead line with a small shorting section of RG-174 in the radiator, allowing it to perform with a good pattern on the 70 cm band. (The shorting RG-174 is inductive on the 2 M band and so just shortens the radiator a bit.) I've built one or two before, and have always found them to be tricky to build, and, frankly, a bit delicate.
>>
>> Electrically they are a great design. The DBJ-1 was intended to be mounted inside a PVC tube and used as a base station antenna, for which it works great. The DBJ-2 forgoes the PVC tube and is intended for portable and emergency use as a roll-up antenna. They always just seem really delicate though, and I suspect something broke on mine when exposed to the cold.
>>
>> I have in mind a new design for a portable multi-band fan dipole VHF antenna that I'll be building soon. Super simple, cheap, a roll-up design, and it will even include the 6 meter band. I'm hoping to get it built this week, so I'll send out info when I get it working.
>>
>> 73,
>>
>> Brandon Clark, KL7BSC
>>
>> https://brandonclarklabs.com/
>>
>> Sent with ProtonMail Secure Email.