[regenfreak]

Thank you gents for the insights.

I would not expect an FSL to have huge gain. Aerial “gain” is all about the unevenness of the reception pattern as no magic is involved, i.e. it can only capture the energy that is there. A physically bigger aerial will likely capture more signal so are we surprised that if you compare a tiny little ferrite rod aerial with a huge box of ferrite rods in a whopping great coil then the latter may do better?

The surprising part is the Q of a massive 1-foot diameter FSL is no better than a single ferrite rod! I also think they don't work as good as they claim to be!!

Here are the measurements that I obtained using 0.56mm enamel wires. I connect the following coils in parallel with a high Q 100pF silver micra capacitor(Qc=10,000).



Q=200 for 75 Mn-Zn 20cm bars of ferrite FSL at 955khz L = 226mH

Q=50 for a 1m hexagonal loop antenna L = 162 microH

Q=125 for a single Mn-Zn 20cm bar L = 160microH

Q =526 for a single Ni-Zn R40C1 20cm bar L = 226microH


The overall Q of a LC tank circuit is:

1/Q = 1/Qc + 1/QL

The common belief is that the Qs of air variable capacitors are high which is not true. In fact the Qs of most aluminum plated capacitors are quite poor and about half of the valve of a high Q silver micra capacitor.

With two Ni-Zn R40C1 toroid stacked 5 X 26 X 8 mm stacked to 16 mm high, Litz 270/46 (0.04 mm), I got Q= 1200. This Ni-Zn R40C1 has created stir in the crystal radio community due to its extreme high Q. However for modern receiver, I have found that high Q is only part of the equation.

I compared the performance of the homebrew superhet 5-valve MW receiver with the following configurations:

1. 1m hexagonal loop
2. one single ferrite Mn-Zn bar
3. 25 ferrite bars in a cardboard tube (solid core)

In all three cases, the antennas track with the three point solutions of the RF LC front end. The 1 m hexagonal loop beats both the single and 25 ferrite bars in the number of weak stations it can receive despite of its poorer Q =50 at around 1MHz.. Surprise? You would expect the 25 ferrite bars antenna would have very high Q and would overload the Rf front end of a valve supehet but it isn't. I think it may be increased core losses which is translated into higher equivalent loss resistance in series with the LC tank.

Tiny loop aerials are the worst of all for the perhaps obvious reason that one side of a loop is very close to the opposite side so any currents flowing tend to be both almost equal and opposite, so do a fine job of cancelling out in terms of the em far-field they generate.

If you read the third link in my first post, the author G3RBJ thinks the classic work by Snelling in Mullard Research Work is all wrong:

http://chiataimakro.vicp.cc:8880/%E5...tions,1969.pdf

Here is the homepage of G3RBJ:
https://g3rbj.co.uk/

Then ferrite antenna calculator in Coil 32 is based on the equation from G3RBJ:
https://coil32.net/online-calculator...alculator.html

There have been billions of valve and transistor radios manufactured using ferrite loop sticks, I am flabbergasted that I have not found a modern textbook provides a definitive theory applicable to ferrite antennas.

Britain once had a problem with convicts. It could hang them, and that made them appear to go away, but it was thought a bit brutal. So someone thought up an alternative that didn't spill blood; Transportation! They would ship them to the far ends of the earth, so far it was thought they wouldn't be able to return. Both methods worked. One day you had a criminal, the next day you didn't.

I wonder if it was Paupa New Guinea or Isle of Man during the Victorian times?

Antenna loss resistance works similarly.

Everything that hits the antenna goes out as:
Losses (heat)
Transmission (what we want!)
Reflection back down the feeder.

In the context of a ferrite bar, the fatter or longer the ferrite bars, the more magnetising heat losses. The efficiency of a ferrite bar does not go up infinitely as the length increases or cross-sectional area, i think the efficiency reach plautea when the length to diameter ratio is about 20 (for a 20cm long ferrite bar of 1cm diameter).

I started off the experiment with 5 ferrite bars, then 10 and 25 sticks..etc I was impressed the performance up to 25 sticks in solid cores. But I didn't see the FSL works that great as the number of sticks goes up to 45, 55 and now 75. Have you ever heard of the sunk cost fallacy? A guy got hooked on gambling after a small win and then he put more big bets and he loses in the end.