Thursday, June 30, 2016

Tuning the flag antenna pattern by adjusting the load

Tuning the flag antenna pattern by adjusting the load. I plotted 100, 300, 500,700 and 900 Ohm for comparison. In the previous design 800Ohm was chosen as the best omni directional value. It could be remotely tuned with a second unit perpendicular and become a electronically rotated unit.

Wednesday, June 29, 2016

Directional Medium Wave short antenna

The quest is for a Medium Wave antenna that doesn't have to be 800 feet long with directional characteristic. Also a chance to learn more about the EZNEC program. This is not and original work. Different parts were gleaned from several sources.

This is the start point. Only 25' long should be doable at most any homestead. An apartment dweller could scale it down and mount it on a wall?
I'm working on an outside antenna so I scaled it up up 16' X 29'.
the transformer is 50Ohm to 900Ohm. More on this later.
I put the model in the EZNEC and here are the results.
It is directional and relative small.
A different view of the pattern

A 3D view from overhead.
What about the SWR?
Sweep from 0.5Mhz to 1.5Mhz looks pretty good.
What about that transformer?
FT50-43 with 7 turns primary and 30 turns secondary should be good. I worked this one out at a friends request and to learn to use NEC programming. Looks like one I may have to try.
One final note the 900Ohm resistor could be from 500Ohm to 1000Ohm range and could be an adjustable as in the first drawing.

Monday, June 27, 2016

The TRB_Mule throughout the ShortWave spectrum

Testing to see if the mule can serve a full spectrum short wave system. Checking from 0.5Mhz to 25.0Mhz. Showing an overhead and side view for each segment. I plotted small segments so they didn't get so congested you couldn't read them.

I think this covers the range it was built for.

It is a little directional. Which way is the house pointing Pat?

Waiting for some interpretation on all those wiggly lines before commenting.

Sadly my attic is not tall enough for the Mule.

The TRB_Mule from a different view

This plot is from a different program but maybe more readable.

This was part of the program so I posted it in case some one is interested.
This is from 4NEC2, another free version of NEC. It also offers ways to modify
the antenna and "possibly" improve it. The problem there is the location defines the
antenna so the mods will not work.

Sunday, June 26, 2016

TRB_Mule antenna

The program I'm using is found here:

The antenna design is from The Radio Boards own Pat Pending.

If I did the plotting correctly it represents his attic mount antenna.

This is the "program".

Thursday, June 23, 2016

Bypass Capacitor

Just an update on the bypass capacitor. In the chart the green line is voltage drop across R10 and the blue is current flow through C5.  The DC bias point is being held constant. Without the capacitor the resistor would drop signal and produce degeneration.

Monday, June 6, 2016

Effect of varying primary inductance

 2.5 volts at 300 ma give 0.75 watts
3.5 volts at 390 ma gives 1.365 watts
3 volts at 400 ma gives 1.2 watts
3.5 volts at 450 ma gives 1.575 watts
3.6 volts at 450 ma gives 1.62 watts

I changed the primary. Since I didn't change the secondary to maintain the impedance matching I might go through the circuit with a constant ratio next.  I just wanted to use spice and see what effect changing the primary. Using a low input in these simulations. If I raise the input the smaller inductance transformer saturates and starts distorting first.  Don't let this emply larger is better. We can't determine a turns ratio and just pick a number from the air. For example if the turns ratio is 10 :1 we couldn't wind a 100T:10T transformer and expect it to work. We have to determine the Z of the primary at the low frequency and set the turns based on the ratio. As the frequency increases so does the Z and the high frequencies will be effected.  The conclusion is to low an inductance an the output level suffers. To high an inductance and the frequency response suffers. It is give and take.