Ferrite rod loading

On both 630m WSPR and 160m FT8 RX I have had great success using the FT817ND and the coax to my 2m big-wheel antenna. Just a mains earth was used in my case. If you cannot use this I expect a simple external ground would do instead.  The tapped ferrite rod is shown. This was used as an ATU. The coax is quite short and the big-wheel about 5m at its highest. At its lowest the coax is about 50cm off the ground. 

On 160m my noise level is S8-9. Despite this I can copy loads on FT8.

Ferrite rods as TX antennas

Something similar has been on before, but I make no apologies for this gentle reminder!

Ferrite rods will work on TX as long as the ferrite does not saturate and the material is fine for the intended frequency.

Low power usually means millwatts or low watts. Some years ago I gave it a try with a random ferrite rod (characteristics unknown) on WSPR with great success. To be honest, it was far better than I expected. I think of ferrites as distorting space with the effective size being proportional to the effective permeability of the ferrite.

I wonder what would happen on 7MHz FT8?

See https://sites.google.com/site/g3xbmqrp3/antennas/ferrite_tx
See https://en.wikipedia.org/wiki/Ferrite_core

UPDATE 1344z: Well I had to try 40m FT8 with the ferrite rod on TX!! With no earths connected and no HF antennas here apart from the highly tuned 10m indoor loop, I have 8 spots already using the FT817ND at 2.5W. Best DX spot was  -7dB S/N from F5NK (936km). Highly impressed! This is the first time at this QTH with this antenna.

UPDATE 2003z:  12 spots of me today so far on 40m FT8 with just the tiny ferrite antenna. I guess the biggest problem is being buried by bigger stations on the same frequency without realising.

Ferrite rods as TX antennas

Now, I am no expert and this is based on personal experiences.

As TX antennas ferrite rods should work. Indeed, my own tests at 80m, 40m and 30m rather prove this. Yes, they will be many dB down on more conventional antennas and can only be used with low power to prevent the ferrites saturating. However, with modes like WSPR they do work. I urge you to try sometime!

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

80m WSPR with the ferrite rod antenna

In all, 46 stations were spotted on 80m WSPR using the ferrite rod antenna. Just one station spotted my 2.5W. There was far more 80m WSPR activity than I expected.  See table below:

80m WSPR spots with
the ferrite rod antenna

80m ferrite rod TX antenna

Jay W5OLF has kindly said keep the antenna. So, later in the week I shall try to resonate it on the correct WSPR and FT8 frequencies and try some NVIS and other TX tests.

Nearly every American I have dealt with has been kind and generous. Jay, thank you!

Ferrite rod TX antennas

My page on ferrite rod TX antennas has been updated and some files added. There is now reference to the work of Giorgio Grisoni I2GSI from Italy.

Ferrite rod antennas work on TX as long as the ferrite is well matched and the ferrite is not in saturation. They may well be inefficient but this may not matter in some cases.

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

Ferrite rod antennas on TX

It is some years since I tried this, but I remember being surprised how well this worked. As long as the ferrite is not saturated, a ferrite rod will work on TX. I tried it on WSPR with the antenna just on the shack table. Of course, WSPR works well.

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!

Ferrite rod transmitting antennas?

OK, I only tried this with WSPR and with low power, but at my old QTH I had a good deal of success using a small ferrite rod as a TX antenna on some HF bands. As long as the ferrite is not in saturation there is no good reason why it should not work. Most problems will occur if the antenna is driven with too much power.

See the link for more details. I have no idea about this ferrite rod's properties but I think it was a fairly standard piece of ferrite rod and nothing too special at all.

Since being in hospital for 3.5 months and moving QTH I have not been able to find the ferrite rod to repeat the tests. My wife moved most of my stuff and it is probably deep in a box somewhere! At some point I guess it will just turn up.

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

Playing with a ferrite rod at VLF

Just for amusement, but with a slight hope it might work, I tried resonating a LW ferrite rod coil (about 3.5mH) at 8.97kHz to see how it might perform as a miniature portable receiving loop in my earth-mode tests.

To test other antennas and VLF preamps, I first connect my 8.97kHz 5W transmitter into a resistive dummy load and check that I can detect the signal strongly some distance away locally (about 10m away only). The emissions from the cables are such that this gives me around 30-40dB S/N on Spectran with the usual settings on my 80cm loop. Switching over to the ferrite rod RX antenna it was hard to tell if a signal was there at all.

So, that's one experiment I'll close and report as a failure. Had it worked, even 10s of dB down, it might have made a magnetic field antenna that could have been deployed mobile. You may recall I tried /M on 8.97kHz a few months ago with my 80cm loop strapped behind the car, until someone pointed out this probably would have invalidated my car insurance and I stopped.  I had vague ideas of dropping the VLF resonated ferrite rod close to the ground behind, somehow fixed from the rear bumper.

Ho hum, another idea bites the dust.

Ferrite Rod TX on 10MHz WSPR

This morning I tried the ferrite rod antenna on 10MHz WSPR TX for an hour. As before, I mounted the ferrite rod VERTICALLY on the wooden desk with all other antennas disconnected -  the only other antennas are a VHF colinear and a 10m halo, and both of these are around 10m away from the shack. Quite a respectable number of spots we obtained with 2.5W from the FT817.

So far I have not managed to get the ferrite rod antenna to match on 14MHz. It may be the losses in the ferrite are starting to impact performance?

I am still unclear how this tiny TX antenna is working: the assumption is a combination of a small amount of radiation off the H-field (ferrite rod coil) loop and some E-field radiation off the coiled vertical section above the tuned part. Then there is still the possibility that it is just acting as an efficient coupler into the house wiring that is doing the real radiation. Whatever, it puts a signal around Europe and occupies a volume with the tuning cap of just 15cm x 10cm x 5cm on the wooden shack table.

More Ferrite Rod TX experiments

Vertical orientation today - good results on 40m WSPR TX

This morning I tried to get a few more WSPR reports on 7MHz using my small ferrite rod antenna. I managed a few only, then after about 20 minutes I decided to try again with the ferrite VERTICAL on the desk. Don't ask me why I did this, but then I started getting a large number of spots!

Now, all other antennas were disconnected and I tried this arrangement in several places around the room and ALL got decent spots. Maybe what I have here is a bit of a hybrid. If you look at the diagram there are about 80turns on the rod beyond the parallel tuned circuit that I assumed was the magnetic loop doing the radiating. Then again you can consider the parallel tuned circuit as a base loading for the 80t short vertical above it. Tuning C1 will bring the whole system to resonance and a low SWR can be found by adjusting the tap point, which turned out to be best very close to the bottom, about 1 turn up. There is no earth connection. I make no claims as to how this works. Some suggest it is just an elaborate coupler into the house wiring, but the very sharp tuning makes me think this is not likely. Also, if this was the case then surely moving it around in the room would make a big difference? Below are the spots for a few hours on 40m.

WSPR spots with the antenna above on 40m today

However it works, it manages to do pretty well. Now I do not believe in "snake oil" antennas, and make no claims for this one: a small ferrite rod will radiate something (H-field). Add a ferrite loaded vertical as well (an E-field antenna) and that will radiate too. What happens in the far field goodness only knows!

When the weather is better I will take the whole kit into the back garden well away from the house and repeat. If it is working without coupling into the house wires (as I think is the case) then results should be comparable. If spots disappear then it will have turned out to be a very good random wire coupler, HI.