Guys I'm wondering if you have any experience in winding ferrite coil antennas... I've got a question for you:

1. Which ferrite antena is better performing ?
Let's say we have a 200 mm ferrite rod and we want to wind a coil to make a MW ferrite antenna, what would be the best way to wind the coil in order to achieve the best performance ?
A short winding coil in a long ferrite like almost all new radios have today or a long coil in a long ferrite like Panasonic RF-2200, RF-1170 or winding half the rod like Radio Shack Dx398/ Sangean 803 did or a twin coil like RP2100 /CCradio has ?
Can anybody share his experience ?

When I was kid and was building transistor radios, the "rules" were to use Litze (multistrand) wire, make the coil like the one on the last picture (but they never mentioned two section coils), and place the coil toward the end of the ferrite rod. A coil arrangement like that can be moved along the ferrite rod, so you can tune it.
Other than this, may be you could do this "scientifically", try all versions and evaluate the performance of it. I am sure people would be glad to read about it.

Good luck, Peter

Just wind it normally with small litz at one end or make it latice wound.

Some of the better antennas were space wound and the wire covered the whole antenna. Lots of math required for those especially if its a flat bar.

The trick is to get high Q. Not extremely high like for a DX crystal set but high enough to be able to cover most of the broadcast band with a 160pF variable capacitor and give the set reasonable selectivity in the front end.

Ive done lots of experimentation with this. Transistor reflex sets usually only have one LC and selectivity and coverage are very important.

Possibly the best antenna Ive pulled from a radio came from a Zenith tube portable. Flat Ferrite bar space wound with fairly good size litz. Had a Q of about 300 at 1Mhz.

Huesby,
If I were you, I would wind it like the one in the second picture. Use Litz as well.

Good Luck!!

wcirco;
Great input ! , thanks... Now How do I get the best Q ?...


orbanp:
I'm currently using litz wire 660/46 and I have made all 3 versions of windings but I'd like to compare results and opinions with somebody who has experience winding coil ferrite antennas.

I learned that "longer" is better and electrical length is dependant upon ferrite material properties as much as wire length. Good ferrites and long coil windings are expensive. Many latter-day radios used just enough to do the job. That being said, it must be properly matched to the front end. Bigger capacitances became available in smaller packages and antenna size came down to meet demand for smaller packaging. In addition, more "local" stations led to acceptance of marginal DX performance. Then along came cell phones and suddenly Bluetooth is considered a music-capable media. What's next, tin cans and twine?
This is how I was told the story by a Senior Engineer while working at Tandy.

As stated the type of Ferrite is extremely important. I normally use antennas taken from transistor radios and rewind them. The type of ferrite in mid 50s Zenith and Motorola tube portables is what Ive found to be the best.

Space winding is an art. It really takes a LOT of experimentation with turns so be warned. If you look at the second picture you posted, near the one end of the loopstick, the windings are fairly close together. They did this for fine adjustment to be able to get the inductance just right. The loopstick was then covered in wax to keep the wire in place. Candle wax works great for this. I have to say, if the antenna is already space wound, take advantage of it. Slowly peel off turns until the desired tuning range is desired. Most Tube radio antennas are made for 500 or 365pf variables. Transistor sets are usually 135pf.

BUT,

If that sounds like too much work you can always wind the coil on the end of the loopstick normally. Start with 75 Turns or so then slowly take off turns until the tuning range is what you want. Many of the transistor radios were done this way especially Zenith. Look at the Royal 500s. For smaller loopsticks (3 inches or less) winding the coil on the most center of the bar is best. That only works if the winding will cover 70% or more of the loopstick. It acts similar to the space wound effect.

The Ferrite material is available Via Ebay but the frequency range of the material may not be fit for AM BCB or SW.

The shape of the material has a big effect. If you notice,

To sum it all up:

Space wind if you positively absolutely need Q. Lets say for a crystal set. Take advantage of space wound antennas when you can if pre wound.

Wind a coil on one end of the loopstick if you are winding a loopstick for a radio with an active device. The difference between Space wound and standard spaced as far as Q is not that much. The difference can be compensated for with larger litz. DO NOT DOUBLE BACK ON THE WINDING!! Only 1 layer of wire on the loopstick is really needed. DO NOT LATICE WIND COILS. The Q suffers greatly. They only did that originally to save space. Notice how only cheap radios and radios limited on space use them.

Look out for old damaged transistor and tube portables that are too far gone. Especially Zenith and Motorola.

Regen sets also benefit from a high Q front end. Adds to selectivity.

Good luck!

Wrap a piece of paper -about the length of the coil you want to wind- over the Ferrite bar, and glue it together, but not to the bar. Wind the coil over it, and then you can experiment by sliding the coil with it's paper vehicle along the bar for the best Q at the desired frequency. You can then use glue or wax to secure it.

Been there done that.

WCIRCO:
Thanks for sharing your knowledge but there's something I don't understand like:

Space wind = leaving a space equal to diameter of the wire ???
standard spaced = winding the wire very close or tightly ??
LATICE WIND = winding the wire one over another ???

I'm not a retard it's just English is not my native languaje
Thanks in advance

Since this topic is about homebrewing antenna coils it was moved here from the Transistor Radios section.

Dave

Space winding on a ferrite rod can be close especially with large Litz. Small diameter fishing line works good.
Positioning depends on the rod. Wound on a paper sleeve it can be adjusted.
Rule of thumb is at least one coil length open on each end of the rod.
There may be some info you can use here:
http://theradioboard.com/rb/viewtopic.p ... 5c3c318d2a

Im not a good explainer either.

Space winding is leaving a space, any amount in between each turn.

Standard spacing is winding the coil with the windings right next to eachother.

Latice winding is double backing over and over the same winding again and again. This creates more inductance in a small area. Efficiency is low.

http://oriharu.net/image/cadu.gif

homebrew and wcirco

Thank you, your help has been very valuable.