Active Ferrite Rod Antenna by OH7SV / OH2NLT

I built an active ferrite rod antenna designed by OH7SV, modified by OH2NLT. The circuit provides ample of signal from 80m to 20m. The efficiency of the ferrite rod used is questionable above 30m. The antenna is a perfect accessory for spending lonely evenings on a hotel with my ATS-3b transceiver. The antenna has sharp nulls on vertically polarized magnetic fields and is quite insensitive to near electric fields. Contrary to the common belief , its directionality is poor for signals reflected by the ionosphere.

Original source:
Active Ferrite Rod Antenna for HF, 08.10.2005 OH7SV
Active Ferrite Rod Antenna OH2NLT

The ferrite rod made by Pramet Sumperk during the Iron Curtain era may be sourced cheaply from
http://ferity.cz/e-shop/en/ferity/548-n2101x144-0000000038430.html
The rod is not as good as the Amidon 61 material counterpart, namely the Pramet N2 material has 2x higher permeability than the Amidon 61 material and it has lower Q and higher losses on HF than the Amidon material. But you cannot beat the price, the rod is about $1.50. If there is enough interest, I may organize a group buy. I may also source the boxes and pieces of the PVC tube.

Tuning control, power off switch, power indicator LED and BNC output on the front side. The ferrite rod is fixed in the PVC tube by injecting hot melt glue at both sides.

Old Russian made polyvaricon placed above the ferrite rod, because the box standoffs would stay in way if the rod was positioned at the top. The box has a convenient 9V battery compartment.

Tiny amplifier board made on a double sided blank board by cutting traces with a needle file. Using two BFR93 low noise transistors as OH2NLT. The output is coupled to the BNC connector by a voltage balun wound on a tiny Amidon 43 material binocular core.

The antenna works well as an accessory to a QRP radio for direction radio finding. It would be cool to add the whip antenna input and 8/cardioid switch. For a single band, I could imagine wiring the amplifier on a additional plug-in board for the ATS-3b.

Lidl "pound shop" FM radio with Alarm Clock

Back in the year 2004 I had a lot of fun with modifying a cheap FM scanning radio to a direct conversion 40m CW receiver.
http://www.kufr.cz/~ok1iak/HAM/PoundShopRadio/index.php3

I was inspired by Hans Summers:
http://www.hanssummers.com/poundshop.html

Hans documented yet another reincarnation of the scanning FM radio, this time with a LCD display.
http://www.hanssummers.com/superdrg.html

Once I stumbled over a FM scanning radio with alarm clock, I hoped I would be able to do a similar conversion and I hoped the frequency counter would be possibly bendable to HF as well.

Front side, showing a FM frequency.

Rear side, closed.

 

Rear side, battery door removed.

Opened. There is a tiny crystal resonator on the rear side for alarm clock.

See the labels on the back of the PCB. It seems there is a general purpose MCU on the board, which may be reprogrammed. There are two tiny crystals on the board, likely one is the 32768Hz clock crystal, the other likely a reference clock for the frequency counter.

There seems to be a combined clock / frequency counter chip under the black blob. There seems to be another chip in a TTSOP10 package, likely the FM receiver chip. One transistor drives the crystal resonator, the other transistor (or maybe an IO) drives the earphones.

Unluckily there is some additional epoxy glue placed over the earphone amplifier and over the FM radio TTSOP10 package. This makes further reverse engineering impossible. The FM receiver chip is certainly not the common TDA7088T kind, which is usually packed in SSOP16.

 

 



That's the end of the story for me. Please let me know, if you can identify the new TTSOP10 FM chip.

73, Vojtech OK1IAK

Kouzelný telefon pro Honzíka

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