Hair!!

 Back in the 1970s I still had hair! This is me using my 2m AM Fredbox to make contacts in Cambridge. It worked really well.

2m Fredbox QSO

This was in 2011 and shows me in QSO with the 10mW 2m AM Fredbox. Many years ago I had a cross channel QSO with it handheld. These days it is hard enough having an FM QSO on 2m!

See https://sites.google.com/view/g3xbm4/home/vhfuhfmicrowaves/homebrew/fredbox. 

Fredbox in Eire

Recently, I was asked permission to reproduce the Fredbox in a PDF magazine in Eire. It was nice to be asked and, of course, I said yes. It is now available.

See https://www.docdroid.net/SgtShtb/crnews1022-pdf .

2m AM, FM and SSB

These days there are few stations on 2m AM. Compared with a few years ago the general level of activity (FM and SSB) is lower with fewer people coming on just for a chat. These days, most go on the internet for a chat.  FT8 activity is higher, but outside contests and lifts, the 2m band is pretty quiet. This is also true of 70cm, at least here.

Many years ago I designed and built the Fredbox. I do not suggest you try to duplicate it, but you may get some ideas from it.

See https://sites.google.com/view/g3xbm4/home/vhfuhfmicrowaves/homebrew/fredbox .

Fredbox 2m QRP

It seems hard to think this tiny rig was designed and built so long ago (1974?). It was rebuilt a few years ago and still works. It must count as one of my favourite all-time rigs. 

I would not recommend trying to exactly copy it, but use it as a source for your own designs. Some years ago, I know one club did a PCB for a version with a loudspeaker amplifier and loudspeaker. I forget who this was.

In its day it had several 100km QSOs handheld and even one of 160km to France handheld even though just 10mW AM. These days, most local QSOs are on FM. In its day, it was a very small rig and much smaller than commercial handhelds.

See https://sites.google.com/view/g3xbm4/home/vhfuhfmicrowaves/homebrew/fredbox .

2m AM QRP

10 years ago I had a QSO with my Fredbox transceiver on 2m AM as the photo shows. 

I still have the Fredbox, but sadly there is little AM still on 2m. 

In its day, AM was an effective mode on 2m. These days there is far less chatting. Apart from organised nets on FM and contests there is, sadly, less activity. Many now prefer the "rubber stamp" exchanges with FT8.

Original Fredbox 2m transceiver photos

Whilst clearing the loft, my XYL came across the original photos of the original 2m AM Fredbox made back in the mid 1970s. It was rebuilt some years ago. The original photos are attached here.

See https://sites.google.com/site/g3xbmqrp3/vuhf/fredbox

2m AM QSO - 100 miles - 10mW - halfwave whip

My  XYL was looking in our loft for some pictures and came across my mobile logbook that I had not seen for over 7 years. I have never managed to get in our loft since my 2013 stroke. 

In the logbook is my Fredbox QSO across the Channel with 10mW and a halfwave whip on 2m AM in 1976. This was one of my all-time best ever QSOs. See logbook page photo below.

Years later the Fredbox was revived and used for some local QSOs again.

See https://sites.google.com/site/g3xbmqrp3/vuhf/fredbox .

Very old Fredbox photo

This photo of me having a chat on my 2m Fredbox must be over 45 years old!

It was taken at our Cambridge flat we moved from in 1975!

The Fredbox is a 10mW AM transceiver that I designed and built for 2m. As most QSOs were with Cambridge local Fred G8BWI, it had to be called the Fredbox! At the time I had hair!!

See https://sites.google.com/site/g3xbmqrp3/vuhf/fredbox for far more infomation, photos, schematic and a video.

2m Fredbox

Many years ago, I designed this 2m QRP AM transceiver. This was in the days when 2m AM was very popular. For its day, it was very small!

I do not recommend you copy this design nowadays, but you may find some useful ideas here.

See https://sites.google.com/site/g3xbmqrp3/vuhf/fredbox

The 2m Fredbox

This was designed in 1974, when I was still "green behind the ears". It got rebuilt much later and still worked well.

The Sixbox came much later.

See https://sites.google.com/site/g3xbmqrp3/vuhf/fredbox .

Fourbox transceiver

G7CKF's Fourbox

Jenny, G7CKF  has now taken the 2m Fredbox design and created a 4m version called the "Fourbox".

Hi Roger,

    I feel I should drop you a line with my thanks and the link below, I've used your QRP AM transceivers as the basis for a 4M transceiver and published it on my blog. I've come back to amateur radio after a 20 year absence and since construction was always my main interest in the hobby I reached for the soldering iron.
http://thekeywordgeek.blogspot.co.uk/2015/05/a-transceiver-for-not-lot.html
There is no sparkling new insight to be had from it as it's pretty much your fredbox with slightly bigger coils. There is no crystal because I am cheating and using a Raspberry Pi clock generator to make my 70.260MHz.
My QTH is IO91lw, between Bicester and Buckingham and rather low lying. Very little 4M activity hereabouts, sadly, so the chances of my actually working anyone with it are slim. But that's not really the point of building, is it.
Anyway, hope you find it of interest, and thanks again for sharing your designs.

Jenny, G7CKF

Fredbox - 2m transceiver

Many years ago I designed and made the 2m AM Fredbox 2m AM transceiver. At the time it was the smallest 2m transceiver I'd ever seen or used.  Several close copies were made.  It worked some impressive DX including several 60 mile handheld contacts and one over 100 miles to Brittany from the South Devon coast.  All these were with whip antennas on the rig and not beams. Most QSOs were with locals. The power was only 10mW AM. It was ideal for contacts around Cambridge where I lived at that time.

Some years ago, I rebuilt the transceiver and had some decent QSOs yet again.

As with the Sixbox, I would suggest the design is taken as a springboard for your own version. It is certainly ripe for further development.

See https://sites.google.com/site/g3xbmqrp3/vuhf/fredbox .

Fredbox derivatives

Since my original Fredbox 2m AM design, a number of derivatives have been designed and built around the world. This is what our hobby is all about. Although the original Fredbox worked well and its results surprised me, it was always ripe for further developments, which is healthy. My Sixbox was a 6m version and at some point, when fitter, I'd like to make a simple 10m AM version for local natters.

See https://sites.google.com/site/g3xbmqrp3/vuhf/fredbox for the original Fredbox. Click on the schematic to enlarge. Other derivative ideas are on my website www.g3xbm.co.uk.   By the way, it got its name from Fred G8BWI who was a disabled local in the Cambridge area back in the 1970s. Fred was a regular contact and he could talk for hours and hours and hours and hours zzzzzzzzzzz. RIP Fred.

Fredbox schematic

Fredbox 2m AM transceiver

The Fredbox was my design for a 10mW AM transceiver for 2m use back in the 1970s. It was rebuilt a few years ago and a 6m version was spun off. The same basic approach would work on 10m and 4m too, but I have not completed versions for these bands.

Even 2m 10mW AM was enough to work across the English Channel handheld on 2m and the 2m Fredbox made several 60 mile handheld QSOs . For quite a while it was used to natter across town in Cambridge. The Fredbox was named in honour of local Fred G8BWI back in the 1970s.

The Fredbox and Sixbox have appeared in G-QRP SPRAT and in Practical Wireless mags. The schematics also appeared in several foreign language magazines too. The circuits are basic and certainly capable of being improved.

See https://sites.google.com/site/g3xbmqrp3/vuhf/fredbox.
See https://sites.google.com/site/g3xbmqrp3/vuhf/sixbox .
 

December's Practical Wireless

The December 2012 edition of "Practical Wireless" has my article about the 2m AM Fredbox and the 6m AM Sixbox transceivers that are described in more detail on my website. These simple QRP VHF transceivers proved to me that you don't need to spend lots of money to make simple transceivers that work. Both have produce interesting QSOs: the 2m Fredbox had several 90km QSOs with one at 160km, despite being only 10mW output and using just a whip antenna!

Today there is not that much AM activity on the bands but I think this is a great pity as the mode has a lot to offer. I do hope the RSGB can be (eventually) persuaded to add 144.55MHz as the AM calling/working frequency in the band plan. It is mentioned (almost lost) in the foot notes, but it needs to be properly shown. For some reason the RSGB seems to have a problem with 2m AM.

I hope others will build simple AM gear for 144.55MHz or crystal up some ex-commercial PMR radios and again enjoy the fun of 2m AM. Second hand AM gear for 4m and 2m can often be obtained for just a few pounds as no-one wants it.

Simple 10m AM transceiver?

Yesterday, someone suggested that I build a simple 10m AM rig. Now clearly the best option would be a DSB transceiver for which I have many of the ideas clear in my head and implemented in my WISPY transceiver for WSPR.

However, I think it would be fun to make a 10m version of my Fredbox and Sixbox QRP AM transceivers. These are to be described in an article in Practical Wireless. For local nattering I think more output is needed on 10m, probably 1-2W AM. A low level series modulator followed by a single stage linear amplifier is a simple way to go on TX. For receive, a super-regen receiver would be fine for local use when the band is not busy. This is 75% of the time at least and almost 100% of the time in the evenings, most times of the year. It would be unsuitable when the band is very active, as currently during the day. A better AM receiver could be built, but nothing beats a super-regen for elegant simplicity, as long as it has an RF amp to isolate it from the antenna.

Maybe this is a quick project for a few autumn afternoons. A few watts of AM on 10m should span several miles locally with a vertical or a dipole.

Simple local ragchewing rigs

The Sixbox 40mW AM transceiver for 6m. Maybe a Fourbox will follow?

The experiments last week by G6ALB and I confirm that to talk over a few kilometres, very little power is needed. Indeed, below 1mW is all that would be needed on any mode, at least on 144MHz. Andrew and I are now thinking about rigs that we can use to simply keep in touch whilst we get on with other QRP tests on bands from VLF to light. One idea is a 4m version of my Fredbox/Sixbox QRP AM transceivers to be called the Fourbox. This would be extremely simple to build and ideal for communication between a couple of stations in adjacent villages. Activity levels on 4m are not that great so we would be unlikely to suffer much interference issues if a super-regen receiver was used as on the original designs. A simple wire dipole in the loft would be fine for an antenna at each end. At 6m I was able to use T37-6 toroids, but at 70MHz I think these would be just beyond their intended design limits. Small airwound coils would probably be OK.

More Sixboxes and Fredboxes

Joe Milbourn has a nice photo of his version of my Sixbox QRP 6m AM transceiver. It looks he's made some changes including the addition of a beefier audio stage on receive, perhaps to drive a loudspeaker.  It also looks like he has added a mic pre-amp. Click the link for Joe's original size image. Incidentally, there are some great photos on Joe's picture site.

Then I noticed a version of my 2m AM Fredbox on a Romanian website. See http://www.garajuluimike.ro/electrice/emitator-receptor-144mhz.htm . This version also uses an LM386 audio amp to drive a loudspeaker.

New G3XBM videos on YouTube

Today I've added a couple more videos to my G3XBM YouTube Channel. They are of the Fredbox 2m AM transceiver and of the FETer 80m CW transceiver. The latter uses just 14 parts but works remarkably well. I hope to add more videos about my projects in the next few weeks.