Monday, January 31, 2022

Proof of concept.

Yes. When I allowed for strays everything fell in place.


It is in how you figure?

 If I have a 200uh coil and I want to tune 1-5 MHz what value should the tuning cap be?

1MHz     2MHz    3MHz    4MHz     5Mhz

126pfd    31pfd     14pfd    8pfd       5pfd

Now if I mark my dial the scale does not match my Vcap values. Why?

Notice the only place it is close is with the hi value cap. The lower the cap the more the strays effect the circuit.

When the dial does not match we can measure the cap and calculate the inductor value.

1MHz     2MHz     3MHz     4Mhz     5MHz

129pfd    34pfd     17pfd      11pfd     8pfd

196uh     186uh     165uh     144uh    127uh

If we do not account for the strays it appears the inductor is changing value.

Maybe another series of scans with the adjusted values is in order?

Friday, January 7, 2022

RC transmitter in sim

 The multivibrator chops the RF signal by switching the darlington pair on/off. The Darlington supplies power to the oscillator.

The antenna is open circuit and the standing waves are there but you can see the switching.

Placing a resistor for the antenna produces a cleaner out put.

I have no data on the antenna. Something else to investigate?

RC transmitter from Radio Constructor mag Sinclaire ST140 ST141

 I am just putting this here before I lose it. I am locked from TRB again. A new member asked about Sinclair transistors.

It works in the simulator using 2N2222 and 2N3904 transistors and 1N914 diodes.

Thursday, January 6, 2022

Using a DBM as a modulator for my KKMOON generator.

 Silly me bought a KKMOON Dual Channel Generator. Nice little generator but it has to be programed. When I used Windows XP I could attach to it and produce a modulated signal. It was a pain programming, instructions not in English. Anywho I no longer have the program and I really want to be able to modulate the signal. My solution may not be the best but it was easy to build and works.

The DBM is simple to build just 3 connectors, 4 diodes and 2 transformers.

It is made on a handy box lid. The 2" X 4" electrical box makes a good rugged project box.

I tried it and it worked well. 

I will make some "custom" cables.

Monday, January 3, 2022

IF transformer coupling continued

The frequency shift because the loading draws inductance from the primary. I can not help but wonder how many times a well built regen failed to function simple because the coils were over coupled. I mean more is better does not away apply. The early builder would go to great lengths to make their coil adjustable for this very reason. 

If you examined the previous post you should have observed over coupling reduces output in an IF transformer.


Sunday, January 2, 2022

IF transformer coupling

 As you scan the sims observe K, OUTPUT currents. You should observe at K=0 there is no coupling. At low values of K the output picks up quickly. At high values of K the signal drops off again. You can not see the whole picture here. In the next series of sims I will show that changing K also changes the coils inductance. Loading the coil shift it inductance.

The output is half as much at K=.5 as it is at K=.25. Why is this?

Winding the cores


This is a commercial transformer. The picture is easier to see than mine. They wrapped the cores to the outside. I put my winding through the centers. I do not think there is much difference in the final transformer. Each pass through the core is one turn. I fold my wire into a hair pin and pass through both sides at once . This is 2 turns. Pushing the ends around to where they started make a primary of 4 turns. Then using a wire twice as long as the first I fold it and put a few twist in the bend, this forms the center tap for the secondary. Passing each end through produces the first 2 turns. Put the center tap on the opposite side as the primary leads. Now make 3 more passes with each end. This produces a transformer with 4 turn primary and center tapped 8 turn secondary.

They used color coded wire which could help avoid confusion. Winding 1 coil at a time helps prevent confusion too. You need 2 of these to make a DBM.

2 transformers, four diodes and a local oscillator will make a receiver. The IF will be audio in a direct conversion receiver. 2 mixers and an IF section will produce a double conversion set. Fun to play with and easy to make.