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Antennas / Re: effective ENDFED antenna f...
Last post by bkmoore - June 08, 2021, 11:12:17 PM
Here's a photo of my 49:1 UNUN consisting of 2 FT240-43 stacked cores. I built it according to Steve Dick, K1RF's reference on EFHW antennas.

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Antennas / Re: effective ENDFED antenna f...
Last post by bkmoore - June 08, 2021, 10:23:06 PM
Quote from: gil on June 08, 2021, 03:55:20 PMThat my friend is a very important statement...

I recently upgraded my K2 with the KPA100 internal amplifier. I built a new UNUN using two stacked FT240-43 cores. According to the reference from K1RF it can handle 300W PEP. I tuned into the Utah Web SDR (ca. 500 miles from my QTH) on 20m and keyed down for several seconds. I saw a very strong S9 + 60 dB signal, loud and clear. It was by far the strongest signal on the display. To make a long story short, I incrementally reduced the power down to 0.1 W. Even at 0.1 W, I still saw a nice clear S5 to S6 signal on the SDR. I could have worked any station in Utah that night with 0.1 W as long as the receiving station's noise floor was low enough.

Assuming that the band is open, there are only three reasons I found QRP doesn't quite get through. There may be more, but these are the ones I noticed:

1. The far field radiation pattern is not the ideal pattern and the station lies within a null. Unless your dipole or EFHW is horizontal and 1/2 wave length above the ground and free of obstructions, you have nulls.

2. Something is defective in your equipment and the antenna isn't radiating at all.

3. The receiving station has a very high noise floor, and your signal falls below it.

When does QRO power help? It helps only in two cases that I can discern:

1. Getting your signal above the noise floor, especially for stations fighting an S8 or S9 noise floor. This seems more common on SSB than CW.

2. Marginal band conditions. Having more power, your signal may only drop from an S9 to an S7, which is better than a QRP signal dropping from an S5 to an S3 and below the receiving stations noise floor.

Should we ditch our amplifiers and go QRP only? Outside of a prepping situation, probably not. The other thing I learned from my little SDR experiment is with each power reduction, I did see a signal strength reduction on the SDR. That tells me two stacked FT240-43 toroids can handle 100W CW without saturating. Otherwise, there would have been no change in the SDR reading until I got below the saturation threshold.

My EFHW can handle 300W PEP, but it's still a compromise antenna. It is too low to the ground and too close to buildings to have a predictable far field radiation pattern. I have no idea what the radiation pattern really is. I need to either get it up 10m in the sky, which isn't really feasible at my QTH, or construct an antenna that doesn't need to be mounted as high. I am considering a delta loop in this case. Further down the road, I would like to build a portable 2 el Yagi and mount it on a 10m military fiberglass push up mast. Probably not the ideal antenna for prepping, but would be a great antenna for field day, camping, or natural disasters and other emergency comms. My intent is to try to get away from using a compromise antenna so that the performance will be more predictable.

73, de Brian
Antennas / Re: effective ENDFED antenna f...
Last post by gil - June 08, 2021, 03:55:20 PM
QuoteI found that increasing the power the connections did not get better.

That my friend is a very important statement...
Thank nyou for sharing. Keep experimenting!
I will too :-)

Antennas / Re: effective ENDFED antenna f...
Last post by am - June 06, 2021, 12:25:24 AM
Hi Gil,

I am far from being an expert and can't give opinions
what is good and what is not - I came here because
i like to be outdoors with my radio - just like you.

I'm watching your videos with interest - that's where
it all started for me.
Admiration for what you do - for popularizing our hobby.

My usual position is on the beach -
I can't stretch wires back and forth there,
because there are a lot of people walking around,
but with a raised fishing rod (which still has
wire on it) - I do not look suspicious.
In my attempt to make more and more dx connections
I found that increasing the power the connections
did not get better.

So I got to ask here, and to show what are my observations
until now.

I'm counting on our community and you Gil.

73 de LZ2DM
Antennas / Re: Simple Dual Band 20m/40m V...
Last post by gil - June 05, 2021, 03:46:42 PM
Hello, I bet you could make a half-wave one by doubling the wire lengths... Like my
PAR 10/20/40... Using a 49:1 or 64:1 transformer of course..

Antennas / Re: Portable UHF Yagi antenna
Last post by gil - June 05, 2021, 03:35:50 PM
Hello. If I remember well, there was no plan so to speak, but a link to an online Yagi calculator...

Antennas / Re: Magnetic antenna query
Last post by gil - June 05, 2021, 03:34:46 PM
Very interesting, thank you!
Antennas / Re: EFHW as an inverted V
Last post by gil - June 05, 2021, 03:31:19 PM
Hello Josefius.

I definitely think it will work, but of course you won't know until you try...

Antennas / Re: effective ENDFED antenna f...
Last post by gil - June 05, 2021, 03:29:06 PM
Hi, so, do you conclude that 4c65 is better than 43?

Antennas / Re: effective ENDFED antenna f...
Last post by am - June 05, 2021, 02:41:27 PM
Hello friends,

today I decided to continue tests with the two transformers
4c65 and 43 - but only with 5W QRP, because at higher power
the transformer with 43 material has losses as seen above.

The first test is in CW mode, and the results from RBN network
are practically the same:

During the test at a ~30m distance from the antenna and using
my tiny Spectrum Analyzer the measurements showed again equal
result for both transformers at 5W -37dBm:

I did the second test with SotaBeams' WSPRLITE with only 100mW:

I achieved very good distances with both transformers
but still approximately the same results:

From the tests so far I made the following conclusions for my self:

1. It is good to know what is the resistance of the endfed wire
so that we can fed it as well as possible.
2. Material 43 is usable - but it is good to have at least
three (or more) primary turns to reduce its losses.
3. The 100pF capacitor gives additional losses.

However, all this is of no practical importance with 5W QRP.

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