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Comparing the Internal vs External Wire Carbon Fiber Mast Vertical Antennas

 A classmate of mine had an interesting question about my recent post on using magnet wire inside a carbon fiber mast as an antenna. He wanted to know if I saw any differences in the signal between the internal wire and the external wire cases. Using the Utah SDR, and GloTEC F2 layer data, I was able to compare the two antennas.

It turns out that just looking at the S meter at that time of day in Utah, there's almost no difference. Both the external and internal wire antennas are between S8 and S9 on the two different days.  The s-meter I was able to view on the Utah SDR station, KD7EFG is also reported as SNR on the RBN. The maximum reading for the exterior wire was 38 dB while the maximum reading from the interior wire antenna was 39 dB.

The two measurements were appoximately 20 minutes apart on different days. The exterior wire antenna readings are from 8:39 AM PST the 7th of Januay. The interior wire readings taken at 8:53 AM PST on the 12th of January. So, the question becomes, did we have similar F2 layers on those two days at those two times?

Turns out, we can compare the F2 layers on those two days thanks to the data analysis system KO6BTY and I have been cobbling together for the last few years.


From No Signal at All to Blaring

The KD7EFG SDR has been fun to watch lately becuase you can,  in the course of a few minutes, verify on the waterfall that there is no incoming signal from the San Francisco QTH, and then a bit later that the signal from here is blaring into KD7EFG as the properties of the F2 layer of the ionosphere change. 

Here's the signal report at KD7EFG onset on 01/07/2026



That corresponds to the 38 dB measurement I mentioned above into KD7EFG on the 7th at 16:27UTC. This is when the antenna was configured with an external wire.

Here are the two  critical frequency readings from GloTEC windowing the time 38 dB was reported  by KD7EFG. The graphs below are made with the GloTEC F2 crticial frequency measurements along the geodesic path between San Francisco and KD7EFG. The path between the two stations is shown in white below.


Note that it passes over four map grid squares. Those four squares correspond to the four data points shown below. The x-axis is measure in degrees swept out along the surface of the Earth with 0 degrees starting in San Francisco and 6.7 degrees corresponding to the location of KD7EFG in Utah.





Here are the F2 maximum height measurements along the path in the same time window.






Signal at onset into KD7EFG on the 12th at 16:48UTC.


Onset at 16:48UTC




fof2 when the signal got loud at 16:53UTC


Loudest RBN report at 17:02TUTC (39 dB)




Finding

The day with the slightly louder signal, 39 dB, and the magnet wire had higher fof2 and the same hmf2. The fof2 value wasn't that much different though. It appears the performance of the internal and external wire versions of the antenna are about the same.


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