Regenerative receiver

 A regenerative receiver uses positive feedback to increase amplifcation significantly. The principle was invented around 1912 by Edwin Armstrong, so the early days of radio. The principle enables you to design one or two tube (or transistor) radio's with loudspeaker output.

The radio has one disadvantage; you have an extra potentiometer to adjust the level of amplification (regeneration in fact). So this type of radio is interesting when you like to fiddle around with buttons and knobs.

I ran into a design of Jack Donio. It is an 0V1. Since I had a bunch of retrieved components from a Blaupunkt tube radio I started building the design.

As you might know I am fascinated by radiostuff from the pre-transistor area; I built this radio with a positive result. I made some small adjustments; the complete PSU was available from the old Blaupunkt radio so I used that. Also I used the tube ECC85 instead of ECC81. I did not make the coil according the instructions but I had one, very similar, in the junk box. 

The radio turns out to be quite sensitive. The EL84 provides sufficient audio output. The frequency range is 9..15 MHz. Last days, especially in the evening, there are a lot of broadcast stations to listen to. I heard China, Bulgaria, Iran AM stations. The best way to receive AM signals is to find the spot where the receiver is on the edge of oscillating. Of course you need a long wire antenna (at least 10 meters).

The variable capacitor on the left is for coarse tuning. The one on the right for fine tuning. The last one is required to tune into HAM radio signals in the 10 MHz and 14 MHz band. To my surprise I heard quite a lot of CW signals. The SSB signals in the 14 MHz are quite hard to adjust to. But not impossible. You need care to play with the fine tune capacitor and the regeneration potentiometer.

 

I also added an EM80, the green magic eye. Just for fun.

I am now in the phase of final adjustments and putting some placards near the controls. It was a fun excercise in building vintage radio in this era of microchips, semi-conductors and plug-and-play transceivers from Aliexpress.

High Altitude scanning

I had the opportunity to use my scanner GRE PSR-225 on the 12th floor of an appartment in Rotterdam Zuid. It was fascinating to experience the easy reception of VHF/UHF signals at this altitude (appr. 40 m above sea level).

                                       Scanner GRE PSR-225 with 70 cm antenna on balcony

Some signals were very loud. Of course the VHF/UHF repeaters in Rotterdam, Leiden and Den Haag.

AM signals from Rotterdam-The Hague airport on 118.200 MHz were crisp and clear. Also marifoon signals from vessels on the Nieuwe Maas river between 156 - 161 MHz were interesting.

The use of  PMR frequencies 433.200 and 433.300 MHz was apparent. I wonder can we, ham operators, use more than 0.5 Watts on those PMR channels ?

I hoped to receive 23 cm signals, but was unsuccesful. I focussed on the Rotterdam repeater at 1298.625 MHz, but nothing heard there.

Anyway it was nice to use my scanner GRE PSR-225 after a long time again. Interesting device for sure ! PSR-225

144 MHz FT8 communications

I was curious to see if an old 2 m transceiver was able to handle FT-8 signals. Therefore I removed the dust from my 40 year old Sommerkamp FT-480R and connected it to my pc via  a simple interface.

After waiting a few minutes, the internal oscillator of the FT-480R appeared to be stable enough to make good FT-8 contacts. Both in low power (1 Watt) and hi power (10 Watt) I could make nice QSO’s around 144.175 MHz. FT-8 activity in UK, B, F and D allowed me to make contacts with the neighbour countries .

145 MHz transverter

Currently I am working on a 145 MHz - 50 MHz transverter. I combined various circuits and built it in Manhattan Style. 

The core is a 96 MHz oscillator that enables me to tx and rx from 144...146 MHz in all modes available (FM, SSB, AM) on the HF transceiver (dial IF 48...50 MHz). 

Blockdiagram is as follows:

Ordered a nice frequency counter and DVM from Ali and drilled some openings in the casing to incorporate them.

Yesterday I made my first QSO with Rob PA0RPA on 145.625 MHz via the Bergen op Zoom 2m repeater (The HF transceiver enables the use of -600 kHz freq shift / 88.5 Hz tone for repeater use)

I still have to connect the 250 uA meter. I will install a simple fieldstrength detection circuit for it.

First results in SSTV mode look promising;

Received from PE1NYG in Pijnacker via SSTV repeater PI1DFT on 144.8875 MHz in Delft.

OZ on 160m

I made some nice QSO's on 160m, 1840 kHz, lately. Of course my longwire antenna is much too short for this band, nevertheless I was surprised by the amount of stations I could see in FT8.

Jan, OZ1ADL, rewarded one of the QSO's with a nice eQSL.

28 MHz activity

I hooked up my FT450 with longwire antenna to explore the 10 meter band. There is a lot of activity ! A lot of stations on 28.074 MHz  FT-8 as well. I made some QSO's. I received a remarkable eQSL card from SV3AUW from Kalamata, Greece. I think the homebrew PCB on his card shows a nice X-tal oscillator, right ?

 

73 from the past

I found a nice eQSL this morning from Urugay in my inbox. It dates back to 2006. In that time I was quite active with PSK31:

Medium Wave LPAM transmitter

I did some experiments with the receiver IC KT0936M lately. I built a simple SW and MW receiver with this chip. To be able to do some experiments with the MW radio I thought it would be a good idea to make a small MW LP (Low Power) AM transmitter. 

                            Medium Wave receiver with KT0936M

For reasons of stability I started with a 1015 kHz crystal oscillator. The modulation of the transmitter is done by a 5W LF amplifier TDA2030A. The output of the LF amplifier goes into the input of the small transformer in the DC supply line.

I used a 2N2219A  as PA stage. I think it delivers about 500 mW. A pi-filter provides the proper interface to the antenna.

MW LPAM Transmitter schematic

With this low power AM modulated medium wave transmitter I have a good radio signal in the house. Of course our radio liscence does not permit the use of this transmitter for broadcast purposes. 

MW LPAM transmitter 

The LF amplifier;

70 MHz Sporadic E contacts

This week now and then the 4 m band opened because of Es.

I made FT8 QSO's with Spain (EA6SX) and Greece (SV2DCD, SV2JAO..) on 70.154 MHz

One QSO has already been confirmed by eQSL:

Path to OH is also open once in a while;

Radio Caroline

Lately I have been experimenting with a KT0936M module on the medium wave. I discovered that Radio Caroline puts a firm signal strength at 648 kHz at my QTH. The music they play is from the 60’s-90’s. Like to hear their music through my 5 Watt tube amplifier 😊

Here   https://www.radiocaroline.co.uk/#648_am.html   you can read that Radio Caroline returned to the medium waveband on 648 kHz AM as a legal broadcaster at the end of 2017, after applying for, and being granted, the Ofcom licence for the Essex and Suffolk areas of South Eastern England. Radio Caroline is using an RF power of one kilowatt from a Nautel ND2.5 transmitter.

More:  https://en.wikipedia.org/wiki/Radio_Caroline