Early days on 2m

My first ever RX outings on 2m were with a derivative of the CQ2 super-regen RX circuit from Practical Wireless back in the late 1960s. The very first signal I ever heard on 2m was G3VEH/P on Caradon Hill in Cornwall. I was located at Kingsbridge in South Devon. I used a small crystal earpiece and a 19 inch whip. The same receiver was later adapted with the addition of an RF amplifier in my Fredbox AM transceiver. These were the days when AM was still king on 2m. The best DX contacts with the 10mW Fredbox were impressive.

A few years ago, I rebuilt my Fredbox and had a few local QSOs on 2m AM. It still works well for something this small and simple. More details of the Fredbox are on my website. Follow the link above.

Tenbox 10m AM RX video

It is hard to contain my enthusiasm for simple transceivers and super-regen receivers! This video shows just how well the RX breadboard for the little Tenbox 10m AM transceiver works. 1uV (-107dBm) is a very good signal and it will still detect a well modulated AM signal at -120dBm. Selectivity is not good with this type of receiver, which is the main drawback. However for its intended application - a simple transceiver for local nattering across town - it should be fine. Some people use super-regens as the IF stage of AM receivers. If a filter is added ahead of the super-regen IF this overcomes the selectivity issue but makes the RX design more complicated.

Tenbox 10m AM rig - a bit more

Although I had little time today, I experimented with adding varicap tuning to the Tenbox AM transceiver's RX section. Only problem was I had no varicaps, so tried using a few different diodes and a transistor as a varicap. 1N4148 and a Germanium diode reverse biased hardly produced any change in capacitance going from 2-12V. I know a 1N4007 works quite well but could not find one. Then I used a 2N3904's base-collector junction and got a few pF of change. In the end I just did as I did in the Sixbox and used a fixed capacitor in series with a 365pF polyvaricon tuning capacitor. This moves the RX frequency as much as I need at around 2MHz maximum.

Sixbox video added

As promised, I've put a small video about the Sixbox 6m AM transceiver on my YouTube channel. You will recall that the Sixbox was a small 40mW AM transceiver derived from the 2m Fredbox. This version is built "ugly style" in a diecast box and has a tunable receiver covering about 5MHz around 49-54MHz. The Sixbox is described in SPRAT 140 and also in the German magazine QRP-Report. It is also described on my website.

6m Fredbox ideas

Looking at project ideas, I am beginning to think about a simple 6m AM transceiver design. The starting point would be my Fredbox design for 2m AM from many years ago. An outline spec would be: 500mW AM crystal controlled TX, simple superregen RX, built as a small modern day "Heathkit Lunchbox" style rig with an RX tuning knob and LS. Such a simple radio would be an ideal local ragchewing radio and would give coverage up to 10-15 miles with a simple vertical colinear antenna, dipole or halo.

A very good example of a 6m superregen (also regen) RX by N1TEV can be found at http://www.arrl.org/tis/info/pdf/9712039.pdf although this is more complex than I would plan to use.