70cms AM using data modules

That font of all knowledge Steve G1KQH has found a useful YouTube video:

"They are all at it now

https://www.youtube.com/watch?v=4leNjynR0DM

73 Steve
http://www.g1kqh.talktalk.net/"

Poppet 160m AM transceiver

This little top band AM transmitter and a companion receiver were first published in the GQRP club SPRAT magazine. This TX version was built by M0DAD. Where the noise floor allows, 160m AM is quite popular for local nets.  There is something nice about "rolling your own" builds and getting satisfying results without spending a fortune. For daytime local use 160m AM is a great mode and rigs are simple. I am still surprised that more is not made of AM on 10m at night for local nets here in the UK.

See http://www.delboyonline.co.uk/m0dad/construcion/poppet_top_band_am_transmitter.htm.

Interest in AM

I note that my most popular blog posts recently relate to Amplitude Modulation (AM). Who said this was a dying mode? Clearly it is not judging by the interest levels shown. RSGB and ARRL please take note.

70cms AM

As you may recall, I am quite a fan of super-regen receivers. Nothing as simple is able to match their AM sensitivity, but they tend to have poor selectivity.

With the availability of very low cost 433MHz modules (TX and super-regen RX) designed for AM data, these modules could be ripe for conversion to ultra-simple 70cm AM voice transceivers. One local friend, Andrew G6ALB, is currently carrying out experiments to see if this is feasible. I hope to work him on 70cm AM using such a rig in the months ahead. Sadly, I am still too clumsy to do any building work - very frustrating.

I am wondering if anyone else has tried these modules in such a circuit? With a simple MMIC PA (50 ohms in and out) the power output could be lifted to around 25mW carrier or more. With V2000 verticals this should be good for local ranges. Even at the low milliwatt level from these QRPp modules several km range should be possible with co-linear antennas.

UPDATE 2310z:   I wonder what sort of power the TX modules typically produce with linear (speech) modulation rather than 5V square wave data modulation? Presumably much less than their rated power, so an add-on PA may be essential?

AM and UK Band Plans

Because of my poor voice (as a result of my cerebellum brain bleed) I tend to use digital techniques, like WSPR and JT65, but I still enjoy AM.  Like many, I've worked transatlantic AMers on 29-29.1MHz with real QRP and simple antennas using AM. It makes a great change from SSB.

One could be forgiven for thinking AM is a dirty word at the RSGB.  In UK Band Plans published in the February 2015 edition of RadCom, AM gets no mention on 28MHz and 50MHz and gets a (begrudging) comment as a footnote only in the 144MHz Band Plan when other modes get "centres of activity" mentions. AM is alive and well in the 29-29.1MHz sub-band. AM on the 144MHz (2m) band here in the UK can be found on and around 144.550MHz. There has been AM on 29-29.1MHz for years and years and years - in fact almost as long as I've been active on the air. Yes, this is in the all-mode section, but why not say this is the 28MHz (10m) AM sub-band? Also, why are 144MHz AM users asked to "consider adjacent channel activity"? AM should easily fit in 6kHz!!

Yet again, AM is being treated as a dirty and outdated mode. Here in the UK, ex-PMR AM rigs ripe for use on VHF can be picked up for virtually nothing and there is certainly room for AM on all bands from 28MHz upwards. AM has its enthusiasts on other bands too, but yet again the RSGB seems keen to kill off this mode. Why I wonder?

Allegedly, a RadCom article on digital TV in the 146-147MHz band was pulled last month at the last minute because "someone at the RSGB" thought it would not fit in the new band! Sometimes one wonders. Maybe the day when I only get SPRAT is closer than I thought? Thankfully, there are many good articles in RadCom.

SSB and AM on CB legal from June 27th in UK

The excellent Southgate News page reports that SSB and AM is now legal on UK CB from June 27th 2014.

I have only briefly operated on CB many years ago and was very disappointed.  I suppose 12W pep of SSB will greatly increase the DX potential on CB. AM is also legal.

We need to watch out for more reports of TVI and hi-fi breakthrough as FM, especially at 4W legal limit, is rarely a problem whereas SSB and AM make such issues more probable. Of course,  some CBers like to use (illegal) add-on amplifiers making matters worse.

I don't think this move will encourage me onto CB any time soon, but it may result in lower cost 10m rigs.

UPDATE 2015z:  Nevada are now selling the President Lincoln 2  (3rd improved version of this model) covering 10m only (as sold - but expandable illegally to cover CB bands) with a £10 discount.

AM and SSB available to UK CBers from July 1st 2014?

According to the Rocket Radio website, AM and SSB will be allowed for UK CB users (for the first time) from July 2014. There will no doubt be a spate of multi-mode rig sales before then. I have no data on frequencies yet. Rigs like the President Lincoln II are 28-29.7MHz only and it is NOT legal to modify these for CB coverage. I guess they will have to get OFCOM type approval for CB versions in the next few months?

10m AM Operation

Ignore what recently published 10m band plans may say - 10m AM is alive and well just above 29MHz with most 10m AM between 29 and 29.1MHz.

Many recent band plans talk of 2700Hz wide SSB in the 29 to 29.1MHz slot. This is rubbish written  by people who don't have a clue! Just take a listen between 29 and 29.1MHz next time the band is open and make up your own minds.

Write to your band plan scribes and ask them to actually USE 10m next time before putting pen to paper. I have written to the RSGB to express my displeasure with their latest 10m attempt:  they blame the IARU.  I see on the RSGB website they have made a half-hearted attempt to clarify 10m AM use - a very poor attempt in my view.

28 to 29MHz is plenty of room for narrow-band modes, even when there is a major contest or the band is wide open. There is space above 29MHz for AM, FM and satellites. 29 to 29.1MHz has lots of AM often with beautifully modulated signals: it is a pleasant change.

In a few years time the whole of 10m will be largely quiet again and we amateurs need to use it for local comms, Es, and the occasional N-S DX or risk losing it to CBers and taxis.

There are plenty of 10m projects on my main website.

Return to 10m and rubbish band plans

I am concentrating on WSPR currently as it does not require me to use my voice, something I find very tiring with my stroke. Just a few sentences and I get quite exhausted. I am told this is to be expected and it should improve over time.

As 474.2kHz is quite quiet in the daytime, I have QSYed up to 10m where I have already been spotted in LZ, RA3,  DK, PA,  G,  GM and 4X  this morning at 2W. This afternoon, I expect the band will be open to the USA. and Canada.

If my voice was better I'd be trying 10m AM, which despite the absolute rubbish in recent IARU and RSGB band plans is still 29 to 29.2MHz. The band plans, surely written by non-users (?), shows 29-29.1 as for use by modes 2.7kHz wide or less. AM gets  a begrudged and confusing  throw away comment in the footnotes. Reading the band plans it reads as if AM on 10m never happens, whereas when the band is open I regularly hear and work (with real QRP)  stateside AM in the 10m AM window, mainly 29 - 29.1MHz. Sorry, but these poorly thought through band plans ANNOY me.

Why can't the 10m band plan reflect what ACTUALLY happens on the band? 28-29MHz is quite enough space for narrow band modes leaving AM where it is (and SHOUT THE FACT that AM exists and is a good  and fascinating mode on 10m), as well as space downlinks and FM  where they are now. Why do these know-alls have to interfere unless they actually understand what actually happens? Band plans are usually a good idea when they actually help. The current 10m band plan is plain WRONG in my view above 29MHz. Write to the RSGB, ARRL etc.. and tell them. AM is 5-6kHz wide NOT 2.7kHz or less and at 29-29.2MHz this is fine. Just damn well leave AM where it is please. Stop messing about!

I also feel it is daft having SSTV and FAX channels mentioned in the 2m band plan but AM only gets a (begrudged?) comment in a footnote. 2m AM is a minority interest but surely deserves a "centre of activity" spot on 144.55MHz so AM folk know where to gather? Ex-PMR AM gear is almost given away and AM gear is simple to build and test. When did YOU last hear a FAX station on 2m? At best, the 2m band plan is a mess. Either leave "special interest" channels out or add an AM CoA in please. AM is NOT the pox, but a good and useful mode!

RANT OVER,but these errors do get my goat.

UPDATE 1745z: lots of 10m WSPR spots this afternoon including plenty from across the pond and at good range:

The band closed transatlantic (for me) at 1840z, well after dark with copy of W8QYT. It may have been even later as my PC shut down the WSPR program after doing some updates!

10m and 2m AM in band plans

I appear to be rapidly losing friends and think I am now effectively banned from the GQRP Yahoo Group.

Why? Because I have made public (GQRP , Dom Baines, the RSGB General Manager and a letter to RadCom) my view that 29 to 29.1MHz should remain the key 10m AM slot which it has been for YEARS and YEARS. I also believe the 2m AM centre of activity (144.55MHz) deserves more than a (begrudged, anti-AM?) foot note in the 2m band plan. To the RSGB it would appear AM is a dirty word.  If I am wrong on this I could be forgiven for thinking so judging by the negative AM comments in the 2m band plan and the total lack of understanding WRT 10m AM currently.

QRP AM rigs are easy to make, cheap to buy (ex-PMR AM rigs almost given away) and a good introduction to amateur radio. I do accept it is not for all.

I am sorry to be a pain, but the RSGB band plans make no sense WRT AM on 10m and 2m currently and I felt compelled to make my voice heard.

Band Plans and AM - Feb 2013 RadCom

In the new February RadCom that just dropped on my mat at lunchtime there is a copy of the band plans for all bands from 136kHz to 134GHz.  What I fail to understand is why does the RSGB appear so anti-AM?

For many years now there has been a clear choice for an AM centre of activity on 144.55MHz. The RSGB has been made aware of this on many occasions and yet still we have a (begrudging) footnote, just about visible if you look hard, saying this is where to look. Even this comment ends with, "although this frequency is not officially recognised within the 2m band plan". Why not? We have a FAX calling frequency listed and goodness knows how many DV Internet Voice Gateway frequencies listed, yet we cannot be allowed an official AM centre of activity properly listed! AM is not a common mode these days, but those who enjoy the mode need to know where to meet on the band. The RSGB is giving no help at all here.

I also get frustrated with the 10m band plan where AM is again almost treated as a disease. Most AM activity has been in the 29.0-29.1MHz segment for years now: this is THE part of the band where AM users congregate, yet the all-mode section with up to 6kHz bandwidth does not start until 29.1MHz upwards! Does no-one who creates these band plans actually listen to see what actually goes on? In the last 30 years I have had many AM contacts on 10m and not one outside 29.0 - 29.1MHz.

So, next time you consider the band plans, please:

(a) Add an AM "centre of activity" frequency into the 2m band plan - it is 144.550MHz in case you don't know.
(b) Show 29-29.1MHz as the AM sub-band in the 10m band plan.

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 progress (10m QRP AM transceiver)

Tenbox breadboard RX -115dBm MDS

Today I breadboarded a simple, but sensitive receiver for 10m AM in the Fredbox tradition. The standard Fredbox and Sixbox circuit was simply scaled down to 29MHz with great results using the breadboard with the Marconi 2022 generator. MDS for a well modulated AM signal is better than -115dBm (around about 0.5uV) which is actually better than I was achieving on 6m and 2m. Not bad for just 2 MPF102 FETs and 1 2N3904. For the tuned circuits (RF amp output and detector) I used a couple of T37-6 (yellow) toroids tuned with 15pF trimmers. There is a 10pF coupling capactor between them.  Of course this is a super-regen with a grounded gate RF amp to isolate the detector from the antenna.

The intended use of the Tenbox is local "across town" nattering when the band is quiet. The selectivity would NOT be suitable for DX use, although I'm sure it would pick up stateside 10m AM stations OK.  I am always amazed by how well a simple super-regen RX works: they just fly for me and are always incredibly sensitive and non-critical. People who have not played with these do not know what they are missing. I highly recommend the RX in the Fredbox

Next stage is to breadboard up a simple AM modulator and TX strip. Again, I shall copy the basic Sixbox design but this time add a linear amp (a few 2N3904s in parallel as in the WISPY beacon) to get the carrier power to a useful level.

In summary, an interesting and productive hour or so after tea.

AM broadcasts on Medium Wave

The BBC recently switched off some of its MW local radio AM outlets for some weeks to see if anyone was listening. Results suggest few people listen to their radios in the UK on Medium Wave any more. I know I am one of them, preferring to use Band 2 FM. We also have a DAB radio but it is pretty useless in the kitchen where FM is perfect. I think it is a signal strength issue.

So, will the BBC switch off all its MW output? Will anyone care? It may soon be that AM will be a dying mode unless we radio amateurs use it and show its strengths.

See www.theregister.co.uk/2012/11/08/dab_am_bbc/.

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.

10m comes to life big time

This afternoon I took a look on 28/29MHz and the band was WIDE open. We are close to the sunspot peak - some would argue just past it - and at this time of the year conditions on the higher HF bands are at their very best. If you have never worked on 10m get on now (especially for the CQWW DX SSB contest next weekend!) and enjoy it whilst it is so very good. In 5 years from now the band will be very very different with just the occasional African and South American openings and Es propagation.

K1IED who worked many QRP AM stations on 10m today

When conditions really are this good, I recommend listening 29.0-29.1MHz for DX AM stations. Today there were some excellent AM amateur signals to be heard from the USA and Russia. K1IED was S9+ with his 250W to a big beam and he managed to work several QRP stations from Europe. In the past I have worked the USA with a few watts of AM but time prevented me having a decent try today. Andy G0FTD managed to work him with just 1W. You can see his video here.

Listening to 29.0-29.1MHz AM when the band is in good shape is like entering a time warp taking you back to how amateur radio sounded in the 1950s and early 60s. Wonderful.

AM lightbeaming down the street

With my wife manning the TX this afternoon and pointing it out of the landing window we managed a daylight speech test today with 100mm optics at both ends at 0.3km using the v.simple AM lightbeam TX described in the previous post. The LED was run with an 80mA standing current. Biggest problem was aligning the TX beam and the lack of talkback, but I managed to get 59+ copy of my wife saying, "I'm bored with this. Come home and have some tea" when I was aligned on the TX beam.

There is no doubt the simple circuit can be refined to improve audio quality when clipping, but it works. The RX is far more sensitive at night too.  I am now finding a way of replacing the XYL for these tests by using another source of speech such as a radio receiver or MP3 player. She is good at cooking and other things, but not at doing optical tests!

Later this week I'll begin experiments with a simple single LED AM 481THz transceiver.

481THz AM transmitter

This morning I took a step further towards making a complete 481THz lightbeam transceiver by breadboarding and testing a simple AM transmitter for use with a high brightness red LED. The circuit could hardly be simpler but works very well. The bias on TR2 is adjusted to give around mid-rail so the LED has a standing bias before audio is applied. Listening (without optics) on my modified KA7OEI receiver head and looking on a scope, the modulation looks good with around 150mA current into the LED.

Mixed results on 160m

The small loft antenna for 160m has produced some impressive results tonight with spots from all over NW Europe of my QRP signal. Best was GM4SLV in Shetland at 5W and OZ7IT at 2W.

But the real reason for erecting the antenna was to allow QSOs on QRP AM over a 3km path to G6ALB so we could use topband for a talkback link when doing other tests. Now, at 9.30pm we went onto 1.973MHz AM to see how easy it would be. It wasn't easy at all! In fact it was very hard work copying even a few watts of AM. The killer is the noise floor that is around S9 both at Andrew's home and mine. On WSPR, with its much narrower bandwidth this is not such an issue, but on AM it ruins the band for what we'd intended. There is no way that 0.25W of AM would make it, certainly not easily with simple rigs as we'd planned. 10W would be OK, but that defeats the purpose. On 70cm AM (yes AM) we had armchair copy between us with about 1W. On 160m FM it was better copy until we dropped the power down and the signal was drowned by the QRN/QRM.

So, what will we do? There is now no point in continuing with the 160m AM transceivers as this isn't going to work at our noisy QTHs with QRP over 3km, sadly. The most probable choice will be 6m AM using my SixBox rig at my end.

The lower HF bands like 160m are radically different from 30 odd years ago when the noise floor was some 20-30dB lower.