Jaycar L15 toroid

[A.Z.]

Hello everybody, I was thinking to build a UnUn for a randomwire using this design

https://vk6ysf.com/unun_9-1_v2.htm

my problem is that I'd prefer using an Amidon or FairRite core and can't figure out the material corresponding to that "L15" one, I've tried searching the intertubes and from the very scarce informations I found, it seems that the L15 should be more or less matching the #61 material, does someone here have some pointer to a "material equivalence" table or the like and/or confirm that the L15 is, in effect, equivalent to #61 ?

[madires]

I've built one with an Amidon FT140-77 (0.5-30MHz) for SWL. I can't say much about its performance since I don't have an NVA. But so far it works fine for me.

[A.Z.]

Thank you "madires", and yes, I already used #43 and #73 in the past and they worked pretty well, but I was curious to know the equivalent material for that "L15" used by Jaycar

[madires]

L15's datasheet states 0.1-2 MHz "practical frequency" and a µ of 1000. Resonant frequency for Amidon #77 is 1 kHz - 2 MHz and µ is 2000. Seems to be the best match.

[A.Z.]

Thank you again, so #77 is the equivalent, I'll try that !!

[profdc9]

If you have a NanoVNA, take your ferrite or and put a couple of turns around it and measure the impedance of the inductor made this way at port 0.  Keep the leads short.  Generally, you look at the frequency where the resistance equals the reactance (R=X).  If the frequency at which this happens is <2 MHz, its a manganese-zinc ferrite core, suitable for MF use (<5 MHz).  If this is greater than 2 MHz, it is a nickel-zinc core suitable for MF/HF use. 

Another cruder way to ascertain the type of core is to measure the resistance of the core when you touch the core with two multimeter probes a few millimeters apart.  If the resistance is very high (>10 Mohm), it is NiZn, and if its less than 1 Mohm, it probably is MnZn.  However, sometimes coatings or paint is added to the ferrite that insulates the ferrite, so it may look like a high resistance material (NiZn) when it is a lower resistance material (MnZn).

You can check out my NanoVNA presentation that includes how to measuring baluns

https://drive.google.com/file/d/1nIkENrhJBO--Bj0yU6yIQrfH-gIgBDqV/view?usp=sharing

[T3sl4co1l]

You could've linked... anything?   I guess this is the datasheet they provide: https://www.jaycar.us/medias/sys_master/images/images/9437376577566/LO1238-dataSheetMain.pdf
But if you were looking at a different product with a different datasheet, I have no idea.

The modest tan δ, lowish µ, low Tc and Bmax, and high ρ, sound like a NiZn material, with a cutoff in the low MHz -- #43 is most similar.

Tim

[A.Z.]

Sorry for not linking the datasheet, and thanks for the infos, but at this point I'm wondering if it's a #43 or a #77, although, given the frequency response of that UnUn I tend to believe that it may be more similar to a #43; thanks again (and no, I don't have a VNA, otherwise I won't be here asking for help  )

See, I'm going to help a friend putting up a random wire antenna, and I wanted a well working UnUn; since in a past I built this one https://vk6ysf.com/balun_9-1.htm but using an FT240-43 instead of the T200-2 which isn't good as a wideband transformer, I thought that the "V2" could be fine as the previous one (except for the core) was, that's why I asked about that L15 equivalence; but given the replies, I think I'll stick with an FT240-43 which already served well (the other randoms had SWR less than 1.5 on all bands from 80 to 10 meters and the radiation efficiency was confirmed by a lot of contacts made with 100W max)

Thank you again

[cdev]

Would you be able to upload it here?

Google is blocking me, claiming that I am doing something, they wont tell me what, that violates their terms of service, even though I am not. I have a totally vanilla, generic setup.

I suspect its because I've expressed (true) opinions that they seem to not like.

You can check out my NanoVNA presentation that includes how to measuring baluns

https://drive.google.com/file/d/1nIkENrhJBO--Bj0yU6yIQrfH-gIgBDqV/view?usp=sharing

Also, I just found this.. Its from an old (2007) PDF.
Image attached. May not be super useful, since it doesn't have jaycar info. But judging by the sites name, maybe some more info could be found there.

Seems like the newer page is
https://www.vkham.com/resources/reference-info/ferromagnetic-information

Looks promising.

[cdev]

Sorry for not linking the datasheet, and thanks for the infos, but at this point I'm wondering if it's a #43 or a #77, although, given the frequency response of that UnUn I tend to believe that it may be more similar to a #43; thanks again (and no, I don't have a VNA, otherwise I won't be here asking for help  )

See, I'm going to help a friend putting up a random wire antenna, and I wanted a well working UnUn; since in a past I built this one https://vk6ysf.com/balun_9-1.htm but using an FT240-43 instead of the T200-2 which isn't good as a wideband transformer, I thought that the "V2" could be fine as the previous one (except for the core) was, that's why I asked about that L15 equivalence; but given the replies, I think I'll stick with an FT240-43 which already served well (the other randoms had SWR less than 1.5 on all bands from 80 to 10 meters and the radiation efficiency was confirmed by a lot of contacts made with 100W max)

Thank you again

Common generic ferrite split beads sometimes work really well for making ununs (or baluns) -they seem to be very good at this. 

But you wind them differently, instead of going around it like you would a toroid you wind it through the middle, keeping the wire inside the cores as much as possible, the effect is you need fewer turns and shorter wire, I suspect this may be a very good way to do it, especially considering the cost. I'm sure it depends a lot on the material, but somebody might easily get lucky if it works well for RFI in a given frequency range there is a decent chance it might work well as a unun or balun. Can't beat the price. 

Three wires twisted together makes a good 9:1 unun. Just a few inches of wire is needed. (Less turns than with a ring core) 

You could also make a balun pretty easily. Try to use identical cores from the same batch. If you have four you could make a balun like the switchable elecraft balun (BL-2)  which can do both 1:1 and 4:1 by switching the output from series to parallel

You'd ideally use four identical cores, and you need a DPDT switch. Make with two binocular cores that balun is really efficient. It can be grounded in the middle. Take care to make it symmetrical.

But even if you just have a single split core you can make a decent working unun, wrap three wires together in a twisted pair like way. If you are using ethernet wire I wouldn't try to wrap it super tight unless you are using thicker wire. Slightly less tight but neat. I did it with two cores and that works quite well. Its just soldered to a BNC female connector and it currently has two alligator clips to connect to antenna and ground.

[HB9EVI]

if it's turning bout matching the core properties, I'd suggest Fairrite material 43; with a ui=850 it's the closest to 1000; on the other side, for frequencies <4MHz I'd rather go with material 77

on the other hand; in reality there is always never a use for a 9:1 unun; its usage is more an urban legend with very little physical facts on its side. let's face it: most of our antennas in the lower shortwave and mediumwave spectrum have, due to their low altitude above ground, a very low real component with a high Xc - so they are far away from 450 ohms real impedance

[cdev]

You're likely working with much much better antennas than I am.

For receive with the kinds of receivers I use a basic 9:1 unun always makes a dramatic improvement in receive, which may be due to the large reduction in noise.  A larger impedance ratio can sometimes work even better, that's basically empirical data, but it does.

Assuming the shield is grounded presto, then the input wire in the unun becomes markedly sensitive to proximity to anything that might be able to act as an antenna.

[HB9EVI]

well, you just start to widely open the door to the discussion about so called 'quiet antennas'
to oversimplify a little, I could say, a 'quieter antenna' is a worse antenna in any way.
of course for reception only, all that matters is the S/N ratio

often not even the antenna is the problem of bad reception, but the feedline and common mode currents on it, they don't only appear when sending, but also when receiving

so, even if the antenna is placed away from qrm, you're going to receive it anyway by the feedline

[cdev]

There are a couple of situations where it makes a huge difference. One is magnetic loops where the antenna is also a pre-selector that wipes off frequency signals off the map while delivering very high voltage signals at the tuned frequency, so strong that the receiver is overloaded and needs an attenuator.  Another situation where impedance matching might be useful is when you have no handy 100 foot vertical wires but do have trees handy.

Tree properly matched can become your vertical antenna and one with a fairly low angle of radiation although on transmit, some power might be lost heating it (Even when I get set up to transmit and have a rig capable of doing so I would not use them for transmitting directly, but I think it would be possible with some kind of "gamma match", But no nails for transmitting, I love my trees.)  In the past it worked so well for receive in fact I think I am going to try doing that again right now. Because they are pretty tall. Too tall for me to get my wires over them easily. Plus its safer as far as lightning to not have the actual wire up in the tree. The tree I am thinking of has already been hit and scarred by lightning. I wish that I had a small portable receiver I could bring outside.

well, you just start to widely open the door to the discussion about so called 'quiet antennas'
to oversimplify a little, I could say, a 'quieter antenna' is a worse antenna in any way.
of course for reception only all that matters is the S/N ratio

[HB9EVI]

well, even a magnetic loop is not only receiving the magnetic field component; its advantage is the narrow passband since it acts as an LC resonant circuit tuned on the receiving frequency.
you can also build a wideband active magnetic loop, where the loop is basically a short circuit with an real component of a few Ohms.

sure, even my Inverted L is mostly acting as a vertical antenne with a capacitive toploading, but it doesn't chance anything on the low real radiation resistance which is no more than 10-20 ohms + the high Xc which has to be compensated by a imaginary component. You cannot compensate the Xc of such an antenna with a 9:1 unun, if your antennas real feedpoint component is only a few ohms

[cdev]

The way Ive been told to do it is to use the unun to get into a ballpark area and then the antenna tuner has less of a problem matching them. Its rare that somebody doesnt need a tuner. But for receiving who cares. It will help but the biggest help comes from the unun.

I think it is the unun because - let me give an example, I have a softrock here, with a piece of coax and a BNC connector with two alligator clips. If I ground the shield onto my radiator and put my finger near the BNC, I dont receive much until I touch it, esecially at lower frequencies.

But if instead of just the BNC I add a small 9:1 unun, the flying lead that's the high impedance input starts receiving stuff even though its just a few inches long, even in MW. And if I hold it, I become a surprisingly decent antenna. Any kind of wire at all, even just 2 or 3 meters will work.  Much better than just using the 50 ohm input. Much less noise, especially. Especially if the ground is semi decent.

Try it.

[HB9EVI]

yea, I heard already so many tales about the 9:1 'magic' unun together with the onboard tuner. to be received like that is for most the undeniable proof of concept. The problem is actually to not radiate some RF at all; people just don't realize, that most of the power remains in the tuning elements and the unun core; it's not much more than a dummy load. that QRP works, is well known, but so many hams think they are qro while they are more like qrp.

another big topic is the confusion between protective earth, grounding and RF earth. Using gutters or radiators as RF earth almost a guarantee to get qrm and rfi/tvi into the system.
most of us live on sites with poor RF earth, like sandy/rocky ground; the aim of RF earth like a radial system around a vertical is to reduce earth loss and improve the effective radiated RF over the low feedpoint resistance.

and no, I'm rather using my active antenna system with a Whip and active magnetic loops for RX

[mag_therm]

I am trying a Fair rite 75 mix with 12 T on antenna side and 2 by 4T on tuner side.
This tuner has a very low impedance when tuned to frequency.

The random wire is 13.3 metre long.
First image is an approximation of reactance variation with frequency.

Second image is with the tuner on to CHU Canada 7850 kHz.
The signal (right-most)  is at about S8 (-79 bBm)
The QRN noise floor is about S5 (-97 dBm)
Just below , ( to the left) spread over 50 kHz, is a QRM "thing" pulsing a comb spaced about 2 kHz every 200 millisec.

[A.Z.]

The random wire is 13.3 metre long.
[...]
The QRN noise floor is about S5 (-97 dBm)

A random is a cheap, easy and pretty decent antenna, but it's far from being a quiet one, if you want to try a "crazy antenna" (RX ONLY!), here's what I came out time ago after much fiddling; I started with a regular linear loaded dipole (also known as "cobra") fed with window line and a 4:1 balun, the antenna worked well enough, but I kept fiddling with it (again used it for RX ONLY), so made a change at time and checked the result, the final config was the following: pick some length (as much as you can) of 3-conductors wire (flat or round) and cut it in half to have the two arms of your LLD (linear loaded dipole), connect the three wires of each arm in series and then connect the two wires (one from each arm) at center to a 9:1 balun (yes, as crazy as it may sound) and now try listening, I believe you'll be surprised