Sixbox 6m transceiver

This dates back many years and is not recommended when 6m is "open" as it has been recently. 

On the other hand, it makes a nice homebrew project and an ideal natterbox across town. 

As I always say, use it as a starting point for your own ideas. For example, add a loudspeaker amplifier, or increase the RF power. Most of my designs are starting points and could usually be improved. Do not be afraid to experiment as this is where a lot of the fun is.

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

Sixbox

There is not much call for AM on 6m these days. That is a pity as designs can be simple and effective. This was my Sixbox that appeared in GQRP SPRAT magazine some years ago, I think. I say think as I cannot remember!

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

Six metres

6m is sometimes called "the magic band" as it can open when least expected to incredible distances. In early July I have often copied Japan on 6m. This is a very long way for a VHF band. There have been some even further distances covered. With the Es season a few watts (or less) can work DX  to at least 1500km.

It is also a useful band for local chats and that inspired my Sixbox. This is not suitable for DX working, but is ideal for local natters.

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

Sixbox 6m transceiver

This design, from many years ago, was designed as a simple rig for local natters. It is ideal for use when the band is not open for DX.

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

6m AM Sixbox

If you are after ideas for a cross town natter box, you may get some ideas from my Sixbox. This is not a DX transceiver, but is useful for chatting locally with friends. If you are making several as a winter project, you may want to do a PCB, although I did not bother.

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

6m Sixbox

Some years ago I had a need for a simple local natter box for 6m so the Sixbox was born. This was not designed as a DX rig but just for local chatting. You may get some ideas from it. It is on my www.g3xbm.co.uk website. 

Sixbox 6m AM QRP transceiver

This was missing from my main website. It has now been added. I did not realise it was missing!

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

Sixbox - simple 6m AM rig

It was way back in 2009 that I designed and built the Sixbox rig. Unlike the Fredbox for 2m, the Sixbox did not use a PCB. 

It is not suitable for DX, but could be useful for local natters.

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

Sixbox 6m AM QRP transceiver

As we slowly progress to "quiet sun" years, it is worth remembering that our VHF bands are useful for local QSOs. Some years ago I designed and built the Sixbox which was a very simple AM transceiver for 6m local communications. It should be easy to build and develop further - maybe with more power and a loudspeaker amp added. I am pretty sure this has been shown before.

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.

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.

GQRP Club SPRAT 140

The latest copy of GQRP's quarterly magazine SPRAT arrived here today and it was nice to see my little Sixbox 6m AM transceiver featured on the front cover, alongside my car keys! Also in this edition was my article about WSPR weak signal beaconing. Since the article was written back in the summer I have been using WSPR almost daily on all bands from 500kHz up to 50MHz.

Just £6 annually gives you GQRP Club membership with 4 article-packed issues of SPRAT magazine a year, as well as access to the GQRP QSL bureau and club sales items such as toroids, QRP frequency crystals, transistors and ICs at good prices. As a GQRP club member, you can get a CD with all 140 editions of SPRAT magazine for just £4. It's worth joining just for this alone. If all other magazines had to go then SPRAT would be the one I'd still get as it is the best.

Sixbox 6m AM .....in Japanese

A few months ago I was asked by Junichi Nakajima-san, JL1KRA, if he could translate an entry on my blog about the Sixbox 6m AM transceiver to use in a Japanese magazine dedicated to AM and its use. Of course I said yes. A few days ago he kindly sent me a copy of the magazine. Now, I can't read Japanese, so I have no idea what the article says but it is nice to see the article in Japanese. Incidentally the magazine called 6mAM shows there is a great deal of interest in AM in Japan.

Since this blog entry was written, the design of the Sixbox has moved on and the revised schematic is on the Sixbox page of my website at http://www.g3xbm.co.uk

Junichi, I do not have your email address but thank you for sending me the magazine, the information and the 50MHz crystals.

Another SixBox QSO

This afternoon I worked G3PTQ in Bottisham, 6kms away with the 50mW Sixbox AM transceiver. Report was RS41 (weak, but 80% readable). Then Terry mentioned he was using a low horizontal dipole, so signals could easily have been some 10-20dB (2-3 S points) stronger had he had a vertical antenna. This little transceiver is definitely proving useful for local 6m contacts.

SixBox (6m) and FredBox (2m) - /P tests

This evening I managed 16kms contacts with both the SixBox 6m 40mW AM transceiver and with the Fredbox 2m 10mW AM transceiver. QSOs were from Aldreth, Cambs, to Swaffham Prior.

Signals from the SixBox were copied by Andrew G6ALB when I was TXing with a 6m 1/4 wave antenna on a magmount on the car roof. On the superregen RX there was solid copy of G6ALB's 6m AM signal. Andrew uses a Diamond V2000 vertical, which recent discussions have confirmed are NOT as effective as a true 1/2 wave vertical on 6m. Clearly if Andrew had even a 2 el beam the QSO would have been a very decent one.

After finishing on 6m QRP, we moved to 2m AM to try some tests with the 2m Fredbox. A solid QSO was quickly achieved with the 10mW Fredbox using the 6m 1/4 wave antenna on the car magmount. This acts as a 3/4 wave antenna on 2m. I then tried the same antenna on the Fredbox handheld. Again, a solid 2-way QSO at 16kms distance. Switching over to a 1/4 wave whip on the handheld Fredbox resulted in a weaker, but just usable signal and QSO (same signal level as on the 6m SixBox). Finally, I tried the Fredbox handheld with a small helical antenna. Although Andrew could just detect this, no real QSO was possible.

So, with the V2000 in use at the far end of the contact, 40mW AM on 6m was not as strong as 10mW AM on 2m. Notheless, it was fun to give both rigs a portable outing and make some contacts.

The picture shows me during the Fredbox QSO using the 3/4 wave whip on the Fredbox.

SixBox testing and "super" 6m DX

Back home in Cambridgeshire now and, sadly, was unable to find anyone within a 15-20 mile radius when in S.Devon with whom to test the SixBox QRP AM rig. This despite calling for several DAYS on the local 6m and 2m repeaters.

The Torbay 6m FM repeater was a good signal and I could access it well, but I heard not one person using it! No-one even replied to a call through it.

I had plenty of 6m DX QSOs on SSB using the magmount on the car and 5W though, and heard (but not worked) some remarkable transcontinental DX on the band from South America.

So, back to more modest aims, I shall be on the lookout for stations in East Cambs to do further range testing the SixBox. Let me know if you have 6m vertical and AM and are likely to be workable with 50mW AM from East Cambridgeshire so we can try a test. I am located in Burwell and have a reasonable takeoff to the west and north.

6m AM and noise

Two local tests with stations on 6m AM have shown just how noisy the band can be when using this mode. M1KTA was 18kms away and M1MAJ around 15kms yet both were not strong on the vertical V2000 antenna on 6m AM even when they were using FT817 rigs at 2W AM. We were going to try the SixBox but signals would have been too weak. Switching to USB made a lot of difference (better) unsurprisingly, as the noise level reduces with the bandwidth.

This goes to show how AM signals do need to be strong to overcome the band noise: when signals are a decent level AM is a fine mode, but it can be hard work when they are very marginal with lots of noise in the background.