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Homebrew Antenna
#1
I have been working on trying to build my first antenna, and have gathered a few things together to get started and wanted opinions/feedback from those of you who have 'done this kind of thing before'.

For the 'mast' of the antenna, I have found a swimming pool telescopic pole over 17ft tall.

[Image: bluewavena302.gif?format=jpg&scale=both&...height=200]

I am going to secure/stabilize it by placing it into a umbrella stand and putting the base of the swimming pool pole into it.

[Image: master:MPC007.jpg?is=360,360,0xffffff]

For the antenna, I am using old TV rabbit ears antennas to make a 2m dipole.

So here is what I have figured so far:

Calculating for 145.130Mhz:

A half wave antenna should be a total of 38.64 inches wide with each of the legs 19.32 inches.

I fasten my TV antennas to a board and make sure there is not more than 38.64 between the two tips with some insulation in between them and solder a connection from the coax shielding to one side and from the center wire to the other one.

Mount to the top of my mast, and stabilize with some guy wires. Still have to figure out the grounding for it...

I plan on taking it to someone with an SWR meter first before attaching it to my radio, but I wanted to get input first.

What say ye?
Jason Petorak
K7JLP
ARRL Member since 2013
Valley Radio Club Member since 2012
------
Blog: Amateur Radio, K7JLP
Gear:
  • Wouxun KG-UVD1P Dual Band Tranciever
  • Baofeng UV-5R Tranciever
  • Tram 1185 Amateur Dual-Band Magnet Antenna
  • 'K7ELI- Special' jPole (2m/70cm) Thanks Eli!
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#2
I say you've got quite the inventive spirit!

I'd give a more in-depth reply, but I don't really have time, so I'll just leave you a quick piece of advice:

The 145.130- repeater is an FM repeater, and 99% of all FM transmissions on two meters are vertically polarized. Also, I'm taking a wild guess at that percentage - but it IS very, very high. Make sure that any antenna you want to use for FM repeater work is vertically polarized and not horizontally polarized - you won't get very good results no matter how good the antenna is. :^)

Also, grounding is good, but not required with a true dipole. It won't change the effectiveness of its' ability to radiate a good signal.

I think the SWR meter is a VERY good idea. I leave mine in-line between my radio and my antenna all time time (On my base station, that is). When you key up on the new antenna for the first time, use the lowest possible power setting that is within the SWR meter's ability to read. SWR meters have minimum power ratings and maximum power ratings - go below the minimum and it won't work. Go above the max and you risk damaging the meter.

Most transceivers can handle a high SWR for a short period of time if the power is low. Testing an antenna on high power is a really good way to find out you have a high SWR AND a newly-fried radio. :^)

Keep us posted - and have fun!
W0ULF 2011+
ex KF7RJU 2011-2011
ex KC7YNP 1997-2007
Rigs: Heathkit RX-1 Mohawk Receiver and HX-10 Marauder Transmitter, IC-7410 Base HF w/AH-4, IC-2720 Mobile Dual Band, IC-V8000 Go-Bag 2m, IC-2820 base 2m/70cm (That goes to Field Day or goes in the other truck when I'm driving it), Kenwood TH-75A and Icom IC-92AD HTs.
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#3
[Image: zu_12.gif]

So I need to make sure I mount the antenna up and down to make it vertically polarized as seen above. Excellent, many thanks for that! The nice thing about a homebrew is I can make it work either way!

I am thinking of getting an SWR meter, but all I seem to find are ones for CB's. Do you have a good suggestion for an SWR meter that is is effective but won't break the bank?
Jason Petorak
K7JLP
ARRL Member since 2013
Valley Radio Club Member since 2012
------
Blog: Amateur Radio, K7JLP
Gear:
  • Wouxun KG-UVD1P Dual Band Tranciever
  • Baofeng UV-5R Tranciever
  • Tram 1185 Amateur Dual-Band Magnet Antenna
  • 'K7ELI- Special' jPole (2m/70cm) Thanks Eli!
Reply
#4
I would recommend the Diamond SX400. I have it and it is good for most FM bands for repeater use. Compared power and reflected readings against my high end Bird meter and it was neck and neck. Satisfied me.


K7UND
Sent from my iPhone
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#5
I love the idea! I have some thoughts though. I am not sure that rabbit ears would be the direction I would go, but if you already have them then use them! For an outdoor antenna I would scrape and solder the telescoping sections as it looks like a spot for corrosion and bad connections. The length of the elements themselves is the critical measurement and the tip-to-tip length is not really going to be a concern.

In regards to an swr meter. Your best bet could be a hamfest, however I have not seen vhf swr meters at all hamfests. I use an MFJ-862 that I found cheap at a hamfest. If you already have a cb swr meter it can be useful. You use the meter in "forward". Then reverse the coax connections and read again in "forward" then figure your ratio. The main problem with using lower frequency swr meters at vhf is that the forward/reverse diodes are not matched at vhf frequencies. you get around that by always using the forward diode. Just google "cb swr meter vhf". I think you will be surprised how close you can get with a good tape measure. I built my 1st j-pole without an swr meter and it is about 1.5:1

Good luck and please advise on how it works when you have it completed!
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#6
I think you have a nice idea. Were you able to pull it off?
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