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October 19, 2017, 08:40:49 AM
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CAP Talk  |  Operations  |  Tools of the trade  |  Topic: VHF base antenna?
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BoxGranch
Recruit

Posts: 15
Unit: SER-FL-466

« on: September 15, 2017, 02:51:37 PM »

I am investigating the idea of acquiring a back up base antenna for a CAP Johnson 5300 radio. This is just me, as a new assistant comms officer, brainstorming a way to improve communications in case of .....

There are, of course, tons of antennas out there, but I am having trouble finding one that covers the 140-158 or so MHz that I know is in the radio. I am not sure if there is anything higher than 158, but in  these parts CAP and USCG are probably the only ones we stand much chance of using. WX is not a TX channel, so no issue with that.

Comet makes one that will do 144-176 and and Browning has one that will do 146-167. Both allege gain, but protecting the transmitter is more important than gain. I'm not sure a high gain is better for CAP anyway since we may be talking to aircraft, so talking in a full hemisphere is preferred to aiming electrons at the horizon.

A possible use will be with a portable mast setup next to a CAP vehicle and running the coax to the radio mounted in the vehicle to extend range. I used to do this all the time with my newspaper radio to excellent effect and figure it could help CAP missions too.

No need to get in a discussion of if I need it, they will issue it or the rationality of spending my own money on something for CAP. This is just investigating and thinking about ways to improve stuff. It is possible that the Wing has something already and I will check that, but I'm fine with spending some of my own money on it. I'm an amateur and can always use it on my ham rig if it turns out not to be needed for CAP needs.

Thanks one and all!
« Last Edit: September 15, 2017, 04:20:33 PM by BoxGranch » Logged
BoxGranch
Recruit

Posts: 15
Unit: SER-FL-466

« Reply #1 on: September 15, 2017, 03:25:40 PM »

Correction, that's a Diamond antenna, not a Comet, I was referring to.
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arajca
Salty & Seasoned Contributor

Posts: 4,146

« Reply #2 on: September 15, 2017, 03:40:41 PM »

A common practice is to get or make a VHF ground plane adapter and a CAP VHF mobile antenna. The is basically an antenna mount (NMO) with 4 radials the you can mount to a pole or side of a building.

I use one of these: http://www.ebay.com/itm/NEW-TRAM-1470-Land-Mobile-Base-Ground-Plane-Kit-NMO-to-N-Connector-SAME-DAY-SH-/181048546074?hash=item2a2755931a:m:mWqKxQR9bEaaItuWzaVMTgw on an old satellite dish antenna mount.
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BoxGranch
Recruit

Posts: 15
Unit: SER-FL-466

« Reply #3 on: September 15, 2017, 04:20:15 PM »

I don't have an SWR meter for high band VHF, so I am reluctant to build an antenna. My friend with a service monitor got flooded out by Irma, so he can't help at the moment, either. Not a problem for RX, but could be for TX.

Thanks!
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BoxGranch
Recruit

Posts: 15
Unit: SER-FL-466

« Reply #4 on: September 15, 2017, 04:26:15 PM »

Taking a closer look, that comes with the radials and presuming the original mobile antenna is on, it is probably good to go as to SWR. I tired a similar kit once that expected you to provide the radials and cut them to length.
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EMT-83
Salty & Seasoned Contributor

Posts: 1,811

« Reply #5 on: September 15, 2017, 07:48:39 PM »

I use a telescoping painters pole to mount my VHF/UHF ground plane on the back of my motorhome. It collapses to 8 feet for storage and extends to 24 feet.
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BoxGranch
Recruit

Posts: 15
Unit: SER-FL-466

« Reply #6 on: September 15, 2017, 08:42:31 PM »

Thanks, I have some of those poles used to hold up military tents you can buy on eBay. I just need to get a stand for them. I used to use photo light stands to push up antennas for cellular or 450 MHz. Those antennas are a bit small and lighter.
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radioconsult
Recruit

Posts: 15
Unit: SWROK001

« Reply #7 on: September 15, 2017, 10:46:26 PM »

Spend $30 on a MFJ 1740 VHF ground plane antenna, some decent coax and call it good.  You do not need to be OCD about SWR you are not going to kill the radio if its a bit high. 
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50 Year Member!
BoxGranch
Recruit

Posts: 15
Unit: SER-FL-466

« Reply #8 on: September 16, 2017, 06:17:59 AM »

Thanks, the MFJ was one of the options I was thinking about. What would you cut it for? 145 MHz keeping it centered on CAP freqs? I usually see 1/4 waves as having a 4-5 MHz bandwidth, but not sure what the SWR rolls up as you go away from the center. Any ideas? How much can this radio take?

I could conceive of work with Coast Guard or some of the inter-operable frequencies, but not very often.

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chief2
Recruit

Posts: 28

« Reply #9 on: September 16, 2017, 06:50:24 AM »

Check out SAL Electronics for VHF Base Antenna
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BoxGranch
Recruit

Posts: 15
Unit: SER-FL-466

« Reply #10 on: September 16, 2017, 07:12:40 AM »

Thanks for the info on SAL. They have some interesting stuff. The Moxon could be very useful for a longer term location. The ground plane converter looks very solid.
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JoeTomasone
Salty & Seasoned Contributor

Posts: 1,659

« Reply #11 on: September 16, 2017, 09:16:27 AM »

Recommended:  http://www.arrowantennas.com/osj/j-pole.html

Used on CAP VHF and Amateur radio for years.    Very durable and portable; great for distressed situations.

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EMT-83
Salty & Seasoned Contributor

Posts: 1,811

« Reply #12 on: September 16, 2017, 12:54:55 PM »

If you want less than unity gain and common mode current issues, a j-pole is your answer every time.
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radioconsult
Recruit

Posts: 15
Unit: SWROK001

« Reply #13 on: September 16, 2017, 09:13:20 PM »

Lets talk some CAP Comm business.  If you have access to ORMS look up your radio, it should be listed as either a base or mobile.  If its a mobile you will need to supply the power supply, coax and antenna.  If it is listed as a base NTC will provide you with a base antenna and coax.  Any questions contact your Wing DC he can explain the process on requesting the antenna and coax. 

Wing DC
National Communications Officer 2014
50 Year Member
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50 Year Member!
CAP9907
Recruit

Posts: 23
Unit: NER-000

« Reply #14 on: September 16, 2017, 09:24:14 PM »

Lets talk some CAP Comm business.  If you have access to ORMS look up your radio, it should be listed as either a base or mobile.  If its a mobile you will need to supply the power supply, coax and antenna.  If it is listed as a base NTC will provide you with a base antenna and coax.  Any questions contact your Wing DC he can explain the process on requesting the antenna and coax. 

Wing DC
National Communications Officer 2014
50 Year Member

This is exactly the way to go; I learned this lesson the hard way... Some Wings use Mobiles as bases and vice-versa. If the radio is not being used in the way intended or as listed, local units are on the hook for the extra accessories.
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16 yrs of service
Wing Director of some stuff
IC3 and a bunch of things below that
BoxGranch
Recruit

Posts: 15
Unit: SER-FL-466

« Reply #15 on: September 16, 2017, 11:33:31 PM »

Let us consider this closed. As noted, I did not want to get into any of the issues of who should do what. I simply wanted to be able to enhance communications. If that involves offending or stepping on toes, then let's not go there. I never expected anyone other than myself to supply anything. After 36 years of making communications work in the news biz, often on my own dime, I am more than willing to do so for CAP which, these days, is more worthy than the news biz. Case closed.
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CAP Talk  |  Operations  |  Tools of the trade  |  Topic: VHF base antenna?
 


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