[Harc] Antenna Elmer needed

[rdkern at reninet.com]

Howard:

In answer to your questions:

(1)wavelength = 299.7/146 (midpoint) = 2.05 meters.

1/2 dipole = 1.025, each element = 51.3 cm :  51.3 cm X 2.54 = 20.2 inches.  I expected my final size to be 18-19 inches.

(2)dipole is easy to play with.  This is inside the house, hanging on the wall.  

(3) my analyzer shows less than 1.5 swr from 144-148 mhz.  A tad over 2 for the 440 range.

(4) I'm trying to figure this out - is my analyzer accurate?  Can something designed as I have it work, or is Btcch right?

(5)"Your previous unit had damage which resulted from high SWR, this would be caused by your set up and use. It will be replaced with a grace warranty replacement. Your standing wave ratio did not match the radio while transmitting; causing internal damage to a variety of components. 


You will need to inspect your coax connectors, antennas, or feed line and identify your SWR issue


SWR can vary depending on weather - to even a slit cable being bent, so it is crucial to identify the issue,"


Thank you for your response - at this point either I'm ignorant as to how to use the VNA (really possible) or it's off by 10% or so.


Richard
kn6fxk

--- harc at humboldt-arc.org wrote:

From: "Howard, KB6NN via Harc" <harc at humboldt-arc.org>
To: Richard Kern KN6FXK via Harc <harc at humboldt-arc.org>
Cc: "Howard, KB6NN" <kb6nn at yahoo.com>
Subject: Re: [Harc] Antenna Elmer needed
Date: Sat, 25 Apr 2020 10:48:11 -0700

Richard,
Yes, and 14ga copper wire, and about 36.25 inches tip to tip.  I made it by making each leg 19" then trimming shorter incrementally.  I used a center insulator with screw terminals that I already had, so I suppose the difference between what it measures and what the formula calculates is due to what's inside the PVC pipe.  See attached.  Now I have questions for you:
1. What formula did you use to calculate the length of your antenna? (two meters is 78.7402 inches) or...
2. Why did you choose to make the antenna a dipole, rather than some other configuration?
3. If your analyzer shows acceptable match, is that for 2 meters of 70 cm?
4. If you have an acceptable match, how do you account for the Btech response?
5. Did Btech say "antenna that was out of tune" or did they say "improper load" or some variation of the latter?
Howard
--
KB6NN

On 4/25/2020 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
> 
> 

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