Hi Roger, VLF,

Thanks for the discussion on the subject. There are different point of views and probably there will never be a common opinion. Hoever it is good to see the different point of views here.
Please comment to the argumentation shown below:

Well, about the " "feels" wrong", let us stay on the example of the QRO station TXing legal 750W in OP8 on 160m. Nothing is wrong with it, i think we can agree here (?). And a lambda/4 vertical antenna is used by many stations of course. This antenna is able to radiate the 3rd harmonic as well, anyway it isn't called a "frequency multiplier".
So what may be a typical 3rd harmonic supression in existing amateur radio equipments? Can someome make a guess?
My guess would be 40...50 dB. When it's 50 dB, then it doesn't "feel wrong" for us. Anyway there are some mW ERP on the 3rd harmonic, even if we ignore it.
Everyone of us can check it with his own equipment today.
750W - 50 dB is 7.5 mW. So obviously 7.5 mW on 53m (160/3) is legel as long as 750W is generated on 160m. This does not feel wrong, right? If we can agree here, then this is a good first step :-) Do we?
-------
Next step:
If there are two stations, who are interested to study HF propagation on 53m, they can do it legally by transmitting on 160m. (same applies for LF or MF or VHF (e.g. 145 MHz => 435 MHz!) of course). But they will quickly ask themselves "why do we have to waste so much power on a frequency that is of no interest for us and cause QRM for other stations on 160m?". So what can they do? Running the transmitter on 53m directly is not legal, but QRO is legal on 160m, with a few mW on 53m! Now, one of them has the idea to add an element which reduces the fundamental frequency (matching for the fundamantal frequency) so that the power on 160m becomes lower. Now if the power of the 3rd harmonic rises, they can reduce the transmitter power, so that the ERP of the 3rd harmonic is still the same as before. Now they have reduced the "QRM" for other 160m stations but the situation on 53m is still the same. Just the supression of the 3rd harmonic becomes lower (ratio 3f/1f), let's say it is 10 dB now. This means 40 dB less power on 160m, i.e. 75mW, and still 7.5mW on 53m. Stations on 160m will be happy with this decision and nothing has changed on 53m. Does this feel wrong now?
Your comments please.
-------
Now a next step for VLF:
Imagine someone is transmitting on 5755 Hz, in combination with a neutral coupling element, a big ferrite transformer which has no narrow band matching to the antenna. There is no power limitation on VLF, so he can generate 10 kW on 5.755 kHz. Would this feel wrong then?
We know 1:9 "baluns" or "magic baluns" for the HF bands which are doing the same! They are "matching" a high Z antenna to a low Z output of a transmitter and this is independent of the frequency, at least on HF. If the 3rd harmonic supression would be 50 dB again, then the power on 17265 Hz is 1 mW! As long as there are no interferences to other services, this does not feel wrong, or does it? And if so, why? Comments please! Thus i think the analogy is NOT "leaving your car across the exit from the local fire station" Or, explain which service is in analogy to the local fire station here??
Next: The radiation resistance of an amateur antenna is much higher on 17265 Hz than on 5755 Hz, 9x higher! So there is a "gain" of 8 dB for the 3rd harmonic. Now, would you call a piece of wire a "frequency multiplier"?? That would feel wrong to me :-)

73, Stefan/DK7FC


Am 03.02.2014 14:47, schrieb Roger Lapthorn:

Like many, I am more than a little concerned about the intentional use of 3rd harmonic reception of a VLF signal. Although I cannot really argue with Stefan's logic, somehow it jsut "feels" wrong.

Very happy to hear of Stefan's 5kHz tests however. Good luck.

73s

Roger G3XBM

On 1 February 2014 16:46, Stefan Schäfer <[email protected]> wrote:

VLF,

This evening and night i'm planning to transmit on 5.755 kHz, using the large antenna, the large coil and the large PA :-)
I don't know what can be expected and how the system works at that frequency. Actually it is just a first test for playing arround and doing some measurements :-)
If some nearby stations want to give it a try, maybe even in 3HD, then don't hesitate :-)

73, Stefan/DK7FC

--

http://g3xbm-qrp.blogspot.com/
http://www.g3xbm.co.uk
https://sites.google.com/site/sub9khz/
http://qss2.blogspot.com/
http://www.youtube.com/user/g3xbm

-- 
73 de pat g4gvw
qth felixstowe, uk
(east coast, county of suffolk)