Are you sure this is really representative ?
I see it more like this: 6 dB of loss is 1 S unit. Many contacts , especially s2s, are given reports between 1 and 5 (so -161 to -137 dB, from 10w) and we know it’s getting hard to copy below S3 sometimes. I feel like loosing an entire S unit in this tight range (6/(161-137)= 25% drop) can make you lose way more QSO’s than what your calculation suggests (6/137 = 4% drop). Or ?
A slightly different perspective: The ARRL Lab measured a noise floor @14 MHz of -124/-138 dBm (preamp off/on) for the Elecraft KX2.
If an SNR of, for example, 6 dB is used for perception with the human ear, this results in an MDS of 118/132 dBm (preamp off/on).
Seen this way, a 2 dB difference could definitely have an influence on the fun factor for ambitious SOTA enthusiasts, hi.
Here is another a bit mathematical and statistical view what 0.5dB can make.
http://ham-radio.com/k6sti/pileup.htm
73 Marek
Then imagine having a big loss like my -6 dB on the transformer I tried to build originally. You go from a 100% chance to be heard to basically 0%. As an activator, the objective is not to bust the pileup of course, but still, I’m convinced that it plays a big role.
I guess the same conclusions can be drawn for losses VS noise floor / QRM. Many chasers have S2-S5 noise floor at home sometimes (or even always). I believe losing one S unit (over an already quite weak signal) would be quite often the difference between a QSO and nothing.
Unless I’m missing something you can’t measure insertion loss of a transformer this way. You need to connect two transformers back to back. The transformer is expecting a very high impedance at the antenna end; not the 50 ohms supplied by the VNA. With two transformers back to back you start at 50, transform up to 2450, then back down to 50. You then divide the loss shown on the meter by 2. Hope this helps.
Mike,
Back to back method requires/assumes two identical transformers.
Considering that most producers give tolerance of 20% on the AL value, it’s not easy to meet “the identical” criteria. However, this is a good enough method to give you pretty close results.
Method with a non inductive resistor as a load for the 49:1 unun is recommended and used by people like Owen Duffy VK1OD or John KN5L
73 Marek
I used a 2450 ohm resistor on the antenna end to fit the 50 ohm of the VNA. I measured exactly the value of my resistor and calculated the appropriate adjustment parameter (17.1 in my tables).
The values I obtained this way match quite well the values found elsewhere, so I guess it’s functional.
A much simpler and more professional way to determine the insertion loss of an HF impedance transformer is to connect the nominal load to the transformer and subtract the calculated value for the load from the measured total insertion loss. Antilogarithmizing this value also gives the efficiency of the HF transformer.
If you want it to be accurate to the decimal place, you can also take the mismatch loss into account when calculating.
This calculation method is described in detail by Owen Duffy in the following publication:
Small efficient matching transformer for an EFHW
https://owenduffy.net/blog/?p=12642
I don’t understand your argument.
KX2’s own noise level is -138dbm, that means S -1. A signal to be decoded requires at least 6db more, i.e. S 0.
The noise level at the antenna on the summit is usually S5 at 40m, maybe S1-3 at 20m and only less at 10m.
When I unplug the antenna plug, the noise always decreases significantly. So - with the KX2 - the sensitivity of the receiver only has a noticeable influence on the higher bands.
But maybe I didn’t understand something correctly.
73 Chris
I do not understand that. Even if you have a 6db loss (I was talking about -2db), that only means that you and your partner hear the signals one level less.
Then why should qso no longer occur? I usually hear chaser with S9 and more. And get a rapport of S7. And even an S2S with perhaps a dual S5 would certainly still come about.
73 Chris
I’m glad you do, because in this case, one S level is indeed not very important. However, it’s quite different for me.
I’m activating in the Pyrénées.
I also noticed that the S-meter of my portable radio (TX500) is very different from my home station (icom-718). An S6 on my icom is barely S3 on my TX500, and I hear better in my TX500 when plugged to the same antenna. Maybe I should get into the settings and see if something can be adjusted because I realised I always have to “lie” when giving reports since my S meter very rarely goes above S7 in reality (Would be S9+ on the icom). Or maybe I’m just doing a silly mistake somewhere, since I’m still new to radio.
The S values displayed by the devices are very different for the same signal.
With the well-known Yaesu FT-817, the display drops to zero with actual S4 voltage.
The current SDRs, on the other hand, are much better. The KX2 displays the correct voltage value. With the definition of S9 at 50uV. I don’t know the Tx500 well enough, but it’s certainly similarly accurate.
But that doesn’t solve your problem.
Maybe you didn’t activate the preamplifier on the TX500.
What antenna length do you use with your EFHW?
How did you hang them?
73 Chris
Most of the time it’s an inverted V. Center is 5.5 m high and ends are 1 m high. 20 m long.
I recently put up my home station again , with a 80 m deltaloop at 10 - 15 m hight. I tried to compare with my sofa setup in the garden and it’s not so bad compared to the big delta loop… However, I tried to chase very briefly with my deltaloop and I mostly heard other chasers but not the activators. I have to try again to confirm though.
I have the feeling that I’m too far for 40m in the day and in the skip zone for 20m. 10m is dead silent here the last few days.
I use exactly the same, sometimes with a more higher center up to 10m and more. I don’t use a pole for this, but throw the wire in a tree using a casting weight.
I guess it’s fine for 40-20m and not too bad for the upper bands.
The skip to your place in the Pyrénées from my place in the north of Germany is mostly a challenge. Too far away for 40m and too short for 20m.
But I’m looking for our first S2S, Rémy.
73 Chris