The radio and the antenna matcher

 

This is the radio to be built.  Note the 20pf trimmer. If the antenna is long enough it could be all the trimming needed.

 The MFJ-16010 would be ideal for the job with a shorter antenna.

 

Note a quick search will find the manual with connecting and tuning instructions.

The hope is we build the unit as presented and it works fine. With our short antenna it probably will not. Adding a MFJ-16010 would be the next step before changing the circuit from the design.

Next thing to consider is the ground. Poor ground can cause you to lose half your signal. MFJ has an artificial ground to consider.

 

It worked so well for Dave. Why does it not work for me?

 This is what we would prefer. Need an acre to build it on!

 The actual antenna is a single wire. It looks like a capacitor  up to 1/4 wavelength.

So Daves antenna is about 1/4 wavelength. (little reactance)

Our antenna is very short and presents a lot of reactance.

 Assuming C2 is the antenna reactance we lose a lot of signal. The radio may be top notch but is deaf because it ears are not in tune. So, what to do?

 By adding L1 C1 we get our signal delivered to the radio input.

So 2 2 word answers - loading coil  - antenna tuner.

 The well loaded - tuned - neutralized input soars.

Next post the radio and possible additional circuit.

 

 

 

Is it a regen?

 The question is can you build a regen around an opamp?

 Things to consider:

How do we modulate and demodulate an AM signal.

What is the number one requirement for mod / demod?

I produced some screen shot that help answer the question.

I have some wheres to be shortly so am just posting the screen shots now 

and will comment further later. 

The shots are in reverse order. Reading from the bottom up makes more since. 

Using one input create an audio output.

Adding a filter separates the signals.

Driving with an AM signal you can see the distortion created. 

Here I tie the inputs together and we see distortion (ripple). This is the non linear action required to demodulate.

 The plus and minus inputs are inverting and non-inverting. Here we have the same phase out as in. The shot above inverts.

Add low Z output

 Note R10.

 

3 stage JFET amp

 Plenty of voltage gain just needs an output stage or transformer.

 It could drive a high Z phone but I want to drive an earbud.

 

Why is it motorboating?

It is motor boating but stops when the meter ground lead is connected to the chassis?

Could it be lead dressing or interstage coupling through the power supply (battery)? 

 

 

2SK2539 SPICE MODEL

 .MODEL 2SK2539 NJF(VTO=-3.1621 BETA=5.01519m BETATCE=-0.5 LAMBDA=2.40112E-2 RD=1.48485 RS=1.48485 CGS=1.05000E-11 CGD=1.40000E-11 PB=5.68050E-1 IS=9.11151E-16 XTI=3 AF=1 FC=0.5 N=1 NR=2 MFG=PHILIPS)