Home > APRS, Daily News, HF, VHF/UHF > 2 Meter Indoor Slim Jim Antennas for Cyclone Season and Other Uses.

2 Meter Indoor Slim Jim Antennas for Cyclone Season and Other Uses.

Yesterday I needed a new project to take my mind off certain things here, so I set about making a new 2 meter antenna. I’d rearranged my shack again and set it up was follows.

- Icom IC703 for HF (40m) APRS 7036.5kHz using an 80 meter vertical loop. Connected to a eePC running AGWUIDigi to crossgate to VHF APRS.

- Icom 706MKIIG connected to iMac running MacLoggerDX (my favourite for DX Cluster use) and connected to an MFJ1700C antenna switch to a choice of two ZS6BKW antennas or a 43 foot vertical.

- Icom 706MKIIG connected to eeePC running HRD and DM780 (my favourite for PSK) and connected to MFJ1700C antenna switch to a choice of two ZS6BKW antennas or a 43 foot vertical. 

- Kenwood TM201A 2m FM transceiver for VHF APRS (145.175 MHz) using a TinyTrak4 as TNC in KISS mode, and connected to eeePC running AGW UIDigi. The antenna is a home-brew 2 meter J-Pole at 10m metres elevation and using a homebrew 4:1 balun.

Both IC706s have a VHF/UHF outlet unused, so I decided to make use of them by constructing two antennas. I will eventually make a nice yagi for long range 2m and 70 cm contacts but for now I was more interested in local access to the repeater and for cyclone season emergency use. I started looking at indoor antenna options and found some very interesting choices. I wanted something I could work on right away, and get going in an hour or two but that would give OK performance. I came across a description and instructions for slim jim antennas made using 450 ohm ladder line. This style of antenna is a bit like a folded over j-pole, basically a u shaped antenna with a short matching stub. Fed with 50 ohm coax and tuned by moving the coax connection points, it was a very easy antenna to make and I already had all the materials. I ended up making two antennas, one for each 706 radio.

I tested on air and got good reports. I got the SWR down to 1.2 to 1 and the antennas are resonant around 146.5 MHz across a fairly broad range.

 

 

 

 

 

Construction of the antennas is outlined in this link. http://www.hamuniverse.com/ke4nu450slimjim.html

My construction photos may assist also-

Start with 1500mm of 450 ohm feed line

bare one end as below

then fold over the end and solder as below

Measure 1473mm to the other end and bare the wire from this point enough to fold over as you did the first end.
Measure 1473mm and bare the ends for a bit longer than that.

Fold over and solder that end as well
Fold over

Solder folded end

Now measure 482mm up from the one end (this will be the bottom)and cut one conductor. Measure up a further 25mm and cut again leaving a little 25mm cutout such as below.
Cut out to make the matching stub

Measure up 102mm then remove insulation up to about 155mm as below.

Measure up 102mm then remove insulation up to about 155mm

Strip some coax of your choice- here RG58 since it is a short run- bare two log tails like so.

Connect your antenna to an analyser or transceiver (on low power) with SWR meter. Attach these bare ends to the stripped section using small alligator clips and move them up and down to get the best match – I failed to take a photo of this. But below is a photo of the stripped section to which you attach these bare ends of the coax. Make sure the braid goes to the stub (short end).

Here is my analyser reading- I got better than this eventually with a bit of trial and error. Got X=0 and SWR 1.2:1

Fit a PL259 to the other end of your coax.

Secure the coax as follows. I added some heat shrink over the top, here prior to shrinking and partly removed to show coax fitting.

One of the finished antennas hanging in my shack.

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Categories: APRS, Daily News, HF, VHF/UHF
  1. ken,m3zkb
    February 28, 2013 at 1:51 pm

    If it works okay, but close to the rf is not a good idea, the same results as with mobiles,=fried brains

    • April 16, 2013 at 10:54 pm

      It is low power and 2 metres from the operator. Much better than a handheld transceiver.

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