Trawoeer Power Pyramid Version 12 - Electrical output from a homemade pyramid

[GPS25]

Here is my second part of my video"Pyramid System Geometry" I hope it will help everybody to build a great Pyramid.Good luck to all of you.
Regards George

http://www.youtube.com/watch?v=DfBj2kYEgwU&feature=channel_video_title

[neptune]

@zhak . Use a nut and bolt to connect the mains earth wire from your cable to one of the mounting holes at the base [bottom] of your transformer . Or connect it to any IRON part of the transformer .

[Pascuser]

I am Back home since one week and I had to delay my pyramid building up to now because of family occupations. I started to work on the pyramid Gegyx made for me, scale 1:1 this time.

As I will load my sand like TT with the CB I give you some information I saw in his video:
the amplifier is a tecnitel AML 35 (you can see tecnitel AML written on it in the video and with the web you see this is the AML 35).

Specifications are here:
http://cb-world.info/Linears/tecnitel/Linear/Technitel_AML35/frames_tecnitel_aml35.htm
We clearly see that it is the same picture for the amplifier in TT's video and in the specifications.

So we see that it is a 30W output linear amplifier and designed for the 27MHz band. This gives us then too the frequency of the transmitter TT used: 27MHz.
He uses channel 1 on the CB.

You can see that wire going from amplifier to the wire winded on the copper tube for sand charging is about 3 meters long. This is important because it has an impact on the impedance for the connexion with the wire winded on the copper tube and the SWR changes according to this length.

The total length of wire with 97 turns and the straight ends is 4.30 meters.

For channel 1 TT used for his CB (you see it on the video) frequency is 26.965MHz in 27MHz band (CB standard), so wave length is 11.11meter in empty space.
Then you must take in account the velocity reduction in atmosphere of light speed and multiply with the factor 0.95

So wavelength is in atmosphere: 11.11x0.95=10.55
A half wavelength is about 5.30 meters
If you use a smith chart (I documented myself today about all this, I did not know this before) you see that this corresponds (4.30 meters of wire instead of 5.30 required for half wevelength) to a SWR a little bit greater than 2.

So the amplifier doesn't break!! This is very important, since a very bad length mismatch gives a big SWR (infinity or near if dismatched) and if greater than 3 it breaks the amplifier surely; safety is only SWR=2 max for the material.

The velocity of light speed in the coaxial gives (0.66 factor) gives a half wavelength of 3.67 meters for optimal transfer, and you must substract the electrical length of the amplifier so what I see is a wire matched here because I see about 3 meters (only vusial estimation); no additional SWR because of it. If you use a smaller or longer wire you create additional SWR.


So TT could use its CB and amplifier because the SWR was a little greater than 2 and this is safe for a short use, less than few minutes. This amplifier has no protection so it was logical that you had SWR<3 surely; if not it would vahe broken in seconds of use and TT uses it for more than seconds to fill in the sand.

If you don't mind about all this your amplifier will burn within seconds of use.
My last one burnt is a preliminary test on an antenna because I think the connector was not enough tightened and the output of amplifier was in an opened circuit.

Now you can charge your sand with a CB, you know what to do. TT did it with the CB and a replication is best with the same procedures not to create more problems than we have.

Mister Trawoeger, could you please confirm the SWR you had while connected to the charging sand copper tube wire and the length of your coaxial used?

[neptune]

Hi Pascuser , and welcome back . That was a very informative article about RF amplifiers and SWR  . Here is some information that may enable you to get that SWR down below 2 .
First set up the apparatus without the amplifier . Just connect the CB transceiver to the swr meter , and connect the SWR meter antenna socket to the Reactor using the length of Coaxial cable you described above . Start with a cable slightly longer than you calculated .Calibrate the SWR meter according to the makers instructions . Now check the SWR on channel 1 and again on channel 40 . If the swr is lower on channel 40 , shorten the coaxial cable by one centimeter . If the SWR is lower on channel 1 , The cable needs to be slightly longer . When you get the SWR as low as possible , you are ready to connect the amplifier . When making adjustments , only switch on the transmitter for a short time to read the meter .I hope this helps .

[Pascuser]

A ham told me that an antenna must have a length an odd multiple of 1/4 wavelength and not 1/2 wavelength. I read again the documentation, and it is 1/2 wavelength with a feed in the middle so you have 1/4 wavelength for each half antenna, he is right.

You can also only use a 1/4 wavelength wire instead of two symmetric 1/4 wavelength feeded in the middle.

With this updated information, resonance is set with L/4=2.64 meters or odd multiple, next one is 7.92 meters. So with 4.3 meters of wire you have 4.3-2.64=1.66 meters too long and this is a 0.157 times the wavelength too long and with Smith chart you read then a SWR=4.2
That is much too big! And the amplifier should have broken within seconds. So you must either reduce the 1.66 length to 1 meter (shorten the wire winded on the copper tube) to have SWR=2 of use an impedance adapter connected to the wire winded on the copper tube.

@Neptune
The information you gave is useful to make the coaxial match the right length for a non additional SWR, but the SWR because of the dismatched antenna is too big with this new information.