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

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.


73

Hello again,


I did forgot to introduce myself - I'm Asen, LZ2DM.
I live in Varna - and I take this opportunity to invite you
to visit my city :)

Friends - I'm glad we have a discussion here
to meet theory and practice together.

Measuring high impedance's is very difficult
and someone can write a dissertation
on this, but I believe and trust my NanoVNA
(in the range of 3 to 15Mhz this is relatively easy) :




I decided to model my antenna in Mmana-Gal software anyway:




The result for the wire impedance (as expected) is  ~ 2100 ohms -

I wound two transformers with the same core size
- one with 4c65 material wound in my way with 3 primary windings and ~ 19 secondary
windings - just like an ordinary transformer. My idea is to use
the small white cable that will provides DC ground (anti-static) and
to ensure the return current in the  wire antenna circuit through this cable.
I guess that this way there will be less current return from the antenna
in the RG58 cable.

The second transformer is wound in the standard way with 43 material
like 1:49 with a 3kV capacitor, as popular and everyone suggest :



First let's check the VSWR of both two transformers:




Both are perfect - 4c65 is spot on with VSWR 1.0, and 43 is VSWR 1.1.

Does that mean they are effective?

I decided to check what are the currents in the wire, using
DIY current probes that will give me relatively right results
for comparison :




Transformer losses wound on 43 material
according to the most popular scheme are nearly 50%!
Looks like my calculations above are correct.

And where does this energy go?
Let's see with the thermal camera:

in the beginning - 43 material:


In the beginning - 4c65 material:


After 10 sec. and ~ 50W of power applied capacitor and transformer
with 43 material become hot and cannot be touched by hand:




While the one with 4c65material  (and probably 61 material too)  even after
very long operation does not heat up at all:



what do you think OM's ?

In the next few days i will try to use my tiny Spectrum analyzer and check all again - this time with decibel comparison.


73

of course you're right - making waves is easy and if we work with 100 watts
there wouldn't be much of a practical difference, but my goal is a maximum effective ENDFED antenna -
working in a field with a 5 watt QRP transceiver  - any decibel loss make a difference.

It is logical to discuss the transformer itself -  the most correct option
for winding 2,3 or more primary windings, which is the low loss material for 14Mhz?

I decided to try a few different materials and a different number
primary windings.



In a 50 ohm circuit we can estimate the core efficiency
measuring parallel resistance Rp of the primary winding
such as 1-50/Rp, and the results for 14.16Mhz are as follows:

4 turns without core (air) = 352 Ohm -> efficiency 86% (~ 1db loss)
3 turns, material 33ri = 341 Ohm -> efficiency 85%
2 turns, material 43 = 210 Ohms -> efficiency 76% (~ 1.5dbloss)
3 turns, material 43 = 452 Ohms -> efficiency 89%
3 turns, material 52 = 526 Ohms -> efficiency 90%
4 turns, material 61 = 2862 Ohms -> efficiency 98%
3 turns, material 4c65 = 2980 Ohm -> efficiency 98%
3 turns, material 77 = 93 Ohms -> efficiency 46% (~ 3db loss)

Logically, the choice here is Ferroxcube 4c65 or 61 material.

I decided also to wind a normal transformer with separate primary and secondary windings
with equal length of wires to form a 1:1 transformation - ie. 50 ohms
to be transformed into 50 ohms :



You can do the same simple exercise at home using a 50ohm dummy load to check VSWR at different frequencies.


At the end my transformer looks like this :



with 3 turns primary and 19 turns secondary on 4c65 core.

Hello OM's, hi Gil,

I'm trying to make an effective endfed antenna
for 20m band.
I don't know why everyone assume that 1/2WL endfed
wire has a 2450 ohm resistance?

I tried in different places with about 10m
long wire (1/2 wavelength at 14Mhz)
mounted vertically on a fishing rod from
fiberglass like this:



Each time the measurement (with my trusty NanoVNA-F, OSL Calibrated)
of the parallel resistance Rp (orange line)
at resonance (Xp = 0, blue line) is about 2100 ohms - as here:



note that at 7.2Mhz (1/4 WL at resonance Xp = 0)
the wire has a resistance Rp of about 120 ohms.

This leads me to think that the transformer for my antenna
for 20m should be 1:42 (not 1:49 or 1:64) !