[FARC] Fw: Homemade 3/8 wave 46 mhz vertical antenna RX only - 5 questions

Wed Oct 21 08:35:33 EDT 2009

Thanks Jeff and Lou.

If ground circuit and ground element mean ground plane then no, I don't have one attached. So, I continued my 3/8 wave testing on my vehicle's universal mobile mount. It works even better there and picks up more of the distant 45.x and 39.x transmissions. I also tried a 17 1/2" antenna that I cut just for 160.x mhz (railroads) and it gets freqs I've never heard active before! It's only a 1/4 wave too. I just salvaged an old mobile whip I had.

I don't plan to transmit at all with it. I only do that with a grounded CB antenna and I used an SWR meter first.

I'm deciding on a book now. Thanks again.

John
jcourteous at yahoo.com

--- On Mon, 10/19/09, Popowsky Louis <popowsk at yahoo.com> wrote:

From: Popowsky Louis <popowsk at yahoo.com>
Subject: Re: [FARC] Fw: Homemade 3/8 wave 46 mhz vertical antenna RX only - 5 questions
To: "Maryland ARCFrederick" <farc at mailman.qth.net>
Date: Monday, October 19, 2009, 3:15 PM

Hi John,
I don't have your address, so I'm answering on the reflector.

My address is popowsk at yahoo.com

A 3/8 wavelength antenna is an uncommon size.  1/4, 1/2, and 5/8 are more typical, and one can find analysis and specifications for those antennas pretty easily.

The Radio Shack 102 antenna is designed as a mobile antenna to be bolted onto a car's bumper, and uses the car as it's ground plane.

You did not describe any kind of attached ground circuit for the antenna so your coax is acting as the ground.  I believe your antenna's reception is due to the length of wire that is stuck in the air.  In this case the antenna probably has an inherent impedance of over 200 ohms and most transmitters would like to see 50 ohms.

DO NOT TRY TO TRANSMIT WITH THIS ANTENNA without an antenna tuner.

An antenna needs a ground element that starts about 1/4 inch from the active element

Two good antenna books are the "ARRL Antenna book" (ordered from ARRL web site) and Joseph Carr's "Practical Antenna Handbook" (ordered at Amazon or Barnes and Noble).

Hope this helps.
Lou

----------------------------------------------------------------------
> Do you know how to answer my questions below? If not, do
> you know Lou 
> Popowsky's e-mail or could you fwd these questions to
> him?:
> 
> Today I bought a RS 102" $19 whip and cut it to 7ft 8 -
> 11/32in to make it 
> into a 3/8 wave for VHF-Low 45.6200 mHz. I used this
> cutting calculator on 
> the web: http://www.csgnetwork.com/antennaevcalc.html. I also
> used this 
> basic design except for that I used a single 1" PVC so only
> the RS whip is 
> used as the antenna and not the pipe:
> 
> So far, it seems to work better than my $29 RS rooftop
> groundplane for some 
> freqs I scan but this is on my deck. I've only had a couple
> of hours to test 
> it. These come in loud and clear and include more
> transmissions than before:
> 
>   45.7400 (MD - MontCo WSSC)
>   39.400 (MD St Pol)
>   46.3800 (VA - Ldn FireDisp)
> 
> This works on the ground plane but doesn't come in at all
> on this 3/8 wave 
> but the direction is obstructed by houses and a hill:
> 
>   46.4600 (MD - Balt Co Fire/EMSDisp)
> 
> This has better voice than the ground plane but has lots of
> static:
> 
>   33.8600 (MD - WashCo-fire)
> 
> Distant frequencies have more static than the ground plane
> but I can hear 
> the voice better. Maybe it's because the temporary test
> location on my 
> ground level deck is not grounded yet. I'll take it down
> tonight & test it 
> more another time. The base is 7ft 8in above the ground.
> Here are my 
> questions:
> 
> 1) Is this concept completely flawed and am I just getting
> these VHF low 
> freqs because it is a long antenna?
> 
> 2) Does the base height above ground need to be equal to
> the wave height? In 
> this case 3/8 wave is 7' 8" so its base is raised that
> high.
> 
> 3) The calculator has these wavelengths as choices: 1/8,
> 1/4, 3/8, 1/2, 5/8, 
> 3/4, 7/8, & full. I've only read of 1/4, 1/2, and 5/8
> wavelengths...is that 
> because those 3 are better?
> 
> 4) Next, I plan to try a VHF-Hi one for 161 mhz (Railroads)
> which that 
> calculator shows as 5ft. 9 - 25/32in for a full
> wavelength.
> 
> 5) Is there a good resource for what I'm specifically
> trying to do?
> 
> Thanks,
> 
> John
> PS, I'll be out of town on Monday so I won't be able to
> make to the meeting.
> 
> 
> 
> 
> --- On Sat, 10/17/09, Jeff Fishman <ljfish1 at comcast.net>
> wrote:
> 
> 
> From: Jeff Fishman <ljfish1 at comcast.net>
> Subject: [FARC] FARC Meeting reminder
> To: "FARC reflector" <farc at mailman.qth.net>,
> "Emcomm" <emcomm at madxra.org>,
> 
> "MADXRA" <madxra at madxra.org>
> Date: Saturday, October 17, 2009, 8:07 PM
> 
> 
> Just a quick reminder that the Frederick Amateur Radio Club
> monthly meeting
> will be held this Monday, Oct. 19, 7 PM at the Independent
> Hose Co. Some of
> the issues we will be discussing will be the future of the
> club station,
> ways to raise money for the club, and programs and
> activities for the next
> few months.
> 
> This month's program will be Joe Durnal NE3R with a
> presentation on amateur
> television.
> 
> See you Monday!
> 
> 73,
> 
> Jeff KB3FIO
> FARC Pres.
> 
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