[Harc] Antenna Elmer needed

[MJ Inabnit]

Hi Richard,

First off, BRAVO for doing your own builds om!  Lots of fun and fairly
easy to build a decent antenna, especially for VHF and UHF since they
are so small!

So you are using a dipole.  You could be doing MUCH better if you built
a vertical and it is still very easy.  But, you are using a dipole to
achieve 0db gain (power in roughly equals power out minus the losses of
coax and connectors.)

The simple formula is 468/Freq in Megahertz.  So our number is
468/146  which gives us 3.2 feet, or roughly 39 inches.

So, I would cut two wires, (or other element material) about 20 inches,
take a SWR measurement then begin trimming equal lengths from each side
until you reach your happy minimum SWR which should be very close to 1:1.5.

this type of antenna is very much like to common 1/4~ magnetic verticals
we use on our cars.  Obviously, the 1/4~ vertical uses the roof as the
other half of the element.

I don't think I would accept the sellers theroy that your antenna is out
of tune, a 1 1/2 SWR is will under 2 and our rigs should happily deal
with that swr.

So you are on the right track if I read your post correctly.

Now, consider building a 3/4~ vertical so you will have some GAIN!  You
simply cut the radiator to 3/4~ length and four 1/4~ ground radials.

Keep up the good work OM!

73
j


On 4/25/20 10:02 AM, Richard Kern KN6FXK via Harc wrote:
> From: Richard Kern via Harc <harc at humboldt-arc.org>
> To: HARC <harc at humboldt-arc.org>
> Cc: Richard Kern at reninet.com>
> 
> I need some assistance with a 2-meter home made dipole.
> 
> I returned by  Btech dual band transceiver to the seller because it
> stopped transmitting.  They've did the repair/replacement and sent it 
> back, telling me I killed my first one with an antenna that was out of tune.
> 
> According to my NanoVNA, it's under 1.5 swr throughout the 144-148 range
> in which I operate.  I did one 10 second transmit on the 444, but it did
> still work after that, at least for a while.
> 
> So:
> 
> if my vna is accurate, the antenna should be fine on 2 meters. 
> 
> My concern is that when it is measured, it seems too short compared to
> the calculations.  Is it normal for a dipole to be about 80% of 1/2
> wavelength?  It's copper wire, probably 14 gauge.  I was expecting
> 90-95% of simple wavelength calculation.  I haven't found anything in
> the literature concerning how much to trim, other than "a little at a
> time until it's swr is minimum for your frequencies). 
> 
> I don't want to hook it back up if I'm operating on bad data (from vna).
> 
> Do any of you have a home-made, confirmed in-tune 2-meter antenna?  If
> so, what is it made of and what are the lengths of the elements?
> 
> I welcome suggestions.
> 
> Richard
> kn6fxk
> 
> 


-- 

wishing you well
Jaye, ke6sls--via the toshiba w/thunderchicken