Ferrite rod TX antennas

Ferrite rods are commonly used as RX antennas on MW and LW. They are compact and efficient for their intended purpose. Their use as TX antennas is almost non-existent.

As long as the ferrite is suitable for the frequency and as long as the ferrite is not in saturation, they may be used on TX. This implies very low power, but we know on WSPR and possibly FT8, long distances may be spanned with very low power indeed. Certainly great ranges have been covered with milliwatts and microwatts.

Some years ago, I did some TX tests with ferrite rods and the results surprised me.

In absolute terms, I have little idea about their loss compared with, say, a dipole. At 630m and 160m, antenna efficiencies are often -30dBd or worse, so they could be far better than we might expect. They certainly are small! Some people have bundled several rods together. I have not tried this.

This is yet another area in which radio amateurs can carry out useful research. Be careful that the ferrite rod alone is doing the work and you are not coupling into a bigger antenna nearby.

In my view ferrite rods "compress space" within the rod. As such, they could be used as magnetic or loading in E-field antennas.Remeber to keep power very low.

See https://sites.google.com/view/g3xbm4/home/antennas/ferrite-rod-tx-antennas .

Ferrite rod TX antennas

W5OLF 1 inch 10m ferrite rod antenna

A few people have experimented with transmitting antennas made with ferrite rods. 

As long as the ferrite is suitable for the frequency and does not saturate it should work. This usually means very low power.

With modes like WSPR great distances can be covered with very low power.

Looking back at past blog posts I saw that Jay W5OLF achieved good results on 10m WSPR with a 1 inch ferrite rod antenna and 500mW RF.

See https://sites.google.com/view/g3xbm4/home/antennas/ferrite-rod-tx-antennas.

Ferrite rod TX antenna experiments in Italy

Riccardo IU1OPK has been doing some very successful tests with ferrite rod TX antennas. on 40m.  For many this may be an answer to compact antennas. We fully accept that a bigger antenna would be better, but these results are good. Below is an extract from the email he sent me. The photos show his arrangement.

"Today I tested the ferrite antenna with WSPR on 40m and it worked well, with power from 2 to 5 watt.
I changed a little bit the design and I found that with a “short circuit” of the upper coil the signals are much stronger... below my scheme and the wspr spots (up to 2600 km).
I attempted some FT8 QSOs with no results but I have been received looking on pskreport website, so even with FT8 some qso should be possible. 

My tests were done both indoor and on my balcony so no strange coupling is noticeable, the antenna was placed vertically, I think that it works like a loop antenna oriented horizontally (not a vertical loaded one since my upper end is grounded).

The “strange” good results around midday and early evening when the critical frequency was around 7 MHz seem confirming a sort of NVIS transmission (quite strong signals and local receivers).

Riccardo's 40m
spots on WSPR

Excellent work Riccardo. Well done.  At the frontier where radio amateurs should be.

Often it is best to ignore experts and just experiment to see what works. Often the so called experts do not know and are just spouting myths they were (wrongly) told years before.

 

Ferrite rod transmitting antennas.

This has appeared before, but I think it is worth repeating.

Ferrite rods can be used on TX as long as the ferrite does not saturate. This means low power.  I like to think of the high permeability as a "shrinking of space".  Indeed this is how I visualise ferrites work on RX.

Being a loop, they can be very narrowband, but will work when frequency is fixed such as with WSPR or FT8.

I have no idea what the "gain" is, nor have I any idea of the ferrite material that I used.  It is some years since these experiments were carried out.  The results astounded me.

See https://sites.google.com/site/g3xbmqrp3/antennas/ferrite_tx

See also https://en.wikipedia.org/wiki/Permeability_(electromagnetism)

Ferrite rod transmitting antennas

This has been posted before, but results may surprise many.

Perhaps I should repeat these tests with FT8 from this QTH. FT8 is not as good as WSPR with weak signals but it is better than CW.

These tests were done at least 6 years ago and I have not tried since.  It must be used with QRP or the ferrite may saturate.

See https://sites.google.com/site/g3xbmqrp3/antennas/ferrite_tx

Found it! Ferrite Rod

For the first time in nearly two years (because of my brain bleed) I managed to get into our loft space today. Quite by chance I came across the small ferrite rod that I used for my MF ATU/loading coil and ferrite TX antenna experiments. It means next autumn I can use a far smaller loading coil on 472kHz. I'd looked everywhere for this without success. Clearly I did not find it in my shack as my XYL had put it in the loft whilst I was in hospital for so long!

More Ferrite Rod TX DXing

This evening I fired up the FT817 and the small 15mm diameter ferrite rod tuned with a 365pF air-spaced variable and have been spotted on WSPR even further away. This time a couple of spots from Norway, the best being LA9JO 2096km away. As someone pointed out, I may be coupling into local wiring and this might help, but the ferrite rod behaves just like a loop with good directivity and matching just as you would expect i.e. a very low impedance tap point is needed for a good match and tuning is extremely sharp. Personally I believe the radiation is all coming from the ferrite rod and nowhere else.

WSPR reports with a ferrite rod TX antenna on 40m (5W into rod)

TXing with a ferrite rod antenna on 7MHz

Just for fun this morning I tried WSPRing on 7MHz using JUST a ferrite rod wound coil and a 365pF tuning capacitor as a tiny loop antenna sitting on the desk. All other antennas and grounds were disconnected fully. I used one of the low tap positions to find a 1:1 SWR position and put the FT817 on 2.5W (3 blobs). The rod did not get warm. The wire used is around 0.5mm enamelled copper with around 60 turns, tapped at every few turns at the cold end.

The ERP was very small, although I have not yet measured it. To my total amazement, I got an immediate -24dB S/N WSPR report from OZ7IT in Denmark at 853km. Just proves how incredible WSPR is and what a powerful tool it is for simple experiments like this.

Ferrite rod TX antenna on 7MHz WSPR - it worked!

Ferrite Rod RX antenna for 472kHz

 In an attempt to overcome my high LF noise level, today I made a small ferrite rod antenna and preamp for 472kHz which I've been trying out on RX. The ferrite rod was just a small 10mm diameter 60mm long rod (i.e. it is a small ferrite rod) tuned with a 365p variable capacitor and fed into an MPF102 gate at high impedance with the output fed to the FT817 via an emitter follower. At the moment the rod is sitting on the bed in the shack. Despite this, it is picking up WSPR from DK7FC.

I shall have to try a larger ferrite rod next and try placing this remotely in the garden away from noise sources. For a first attempt this is encouraging.

The prototype used to receive DK7FC and G3ZJO

UPDATE: later I tried the 60mm ferrite rod and preamp on 500kHz and copied G3ZJO on several occasions. 

500kHz ATU video

Just put a short video of my tiny ATU for 500kHz onto YouTube.

Ferrite rods as transmitting antennas?

Assuming one is running very low powers (milliwatts) and use (say) 10 ferrite rods "in parallel" for the core is there any reason why a single thick turn on a ferrite rod, suitably tuned and matched, would not make an effective transmitting loop antenna on the lower HF bands or 500kHz? As long as the core doesn't saturate I cannot think why this would not be feasible.

I have just been told about a Yahoo group for people experimenting with ferrite rods. The owner, John Popelish, experimented some time ago with stacked ferrite toroids to make a ferrite rod.

http://groups.yahoo.com/group/ferriterodantennaexperimenters/