AM Transmitters for Vintage Radios

[radium98]

Thank you.

[outis]

Some interesting dutch designs on this site.

Here's a few aerial ideas to try.

http://www.pa2e.nl/jackdonio/radiomorni ... tenne.html

http://lpam.nl/antennes.html

You can use your browsers settings to translate to english.

Hi, I have been looking into the "Helical Antenna" in the second link above.
It gives as components:
- Gray tube of 40 mm with a length of 2 meters. OK that something I can get

100 meters VD wire of 1.5 qmm (black) - now what is a VD wire? (seems to be a German term)

3 x aluminum pipes with a diameter of 10 mm and a length of 50 cm - that's less easy to find (unless one can get a dipole and cut it in the appropriate lenth.

.....

[RF-Head]

It's a dutch site and we use installation wire (VD Wire)

[jvok]

Thats usually sold as "conduit wire" or "singles" in the UK.

B&Q sells 10mm aluminium tube

[outis]

Thank you all about the VD wire.
The project looks much more tidy now, and the next step will be to put battery in the box too.
Range on 900-1000KHz area, for the version, using the BC107 NPN transistor, 8mm ferrite rod, when working on a 1.30V source is 1ft. on 8V goes to 6-7ft (all with no antenna to speak of other than the black wire in the photos and no grounding.)
Same design using the BD141 goes further on 8V and if small telescopic antenna is connected and with grounding it can cover the whole house. But the BC107 version shows much less FM effect and is more stable in frequency than the one with the BD141.
The sound on all old radios (from a 1959 with valves through transistor based of the 1960s to a 1989 with IC) is superior to the actual modern DAB/DAB+ radios and the iPhones and Tablets I have used to feed the TX with audio.
Evidence that AM can sound great, at least on old radios.

My questions now:
- Could I use the "ground" of household power wiring as ground?
- In the past I had heard of AM radio using the mains socket (like the powerline WiFi networking today) - I remember that how AM radio operated in American Universities. Any idea or suggestion/comment about this possibility?

[Nige from Brum]

Outis,

I wouldn't use the household earth, but attach a ground wire to a nearby radiator. The wire can be as long as needed.
Cold water pipes used to make good earths, but these days a lot of cold water systems have plastic piping somewhere in the system. The pipes that bring water to your house tend to be plastic as well, so they dont make such an effective ground.

[outis]

Yes, thank you, I do just that, connecting earth to a metal radiator pipe. But in this case I am not talking about that.
I am talking about what was known (and now almost forgotten it seems) as "Carrier Current" broadcasting. The idea is to use the powerline wiring instead of an antenna. Like the powerline networking works today. Used to be popular with Campus radio stations in the US.
In the links you can see how it works. Since my aim is not to send the signal miles away but only for it to be available throughout the house it looks attractive.
http://k6prk.org/CARRIER%20CURRENT%20AM ... MITTER.HTM
http://www.gregssandbox.com/wocr/carrier.htm
https://darkliferadio.proboards.com/thr ... ng-circuit

[Albert H]

The biggest problems with power line radiation are twofold -

• It's horribly inefficient: we had to run over 8 Watts into the coupler on one University system I did back in the 70s, and we still didn't cover the whole campus reliably.
• The coupler to get the RF onto the mains cabling is tricky to make and requires some expensive components if it's going to be safe!

Remember - the Yanks have a mains system that's just 55V either side of earth, whereas ours is much less forgiving!

[outis]

The biggest problems with power line radiation are twofold -

• It's horribly inefficient: we had to run over 8 Watts into the coupler on one University system I did back in the 70s, and we still didn't cover the whole campus reliably.
• The coupler to get the RF onto the mains cabling is tricky to make and requires some expensive components if it's going to be safe!

Remember - the Yanks have a mains system that's just 55V either side of earth, whereas ours is much less forgiving!

Yes of course. But I only want to have signal from a low power transmitter to the house which is much smaller than a campus. Even a feet from the outlets will do.
As for the coupling, here is the thing. Powerline networking uses quite a simple couplers, and similar power. It cannot be that much different.
If you look at the links in the previous post you'll see "Coupling was usually done with a complicated network of inductors and capacitors. This was a difficult task when you think about it. A typical AC line at 60 hz was basically zero ohms or ground. At 650 khz, it was just high impedance enough that we could modulate it with low power transmitters. The problem was tuning the coupling. Since the power load changed all day as people turned off and on equipment, it was impossible to use really good inductive coupling. Therefore, a simple capacitive coupler was easier and worked just as well. You take a ten watt transmitter and hook it to the power line with a .1 1kv capicitor and that was it!"
Or in the pics.
My idea has been to connect as in the pic, ground to the socket's ground and the antenna to the neutral. Perhaps use an .1 1kv capacitor as above.
Or perhaps what the diagram shows here: https://darkliferadio.proboards.com/thr ... ng-circuit

https://web.archive.org/web/20161021033 ... MITTER.HTM

[yellowbeard]

Ifn you're just looking to do your gaff then I would stick with the transmitter you got and make a resonant loop antenna to go with it. You could knock one up out of the junk box to see if it does what you want - keep you busy for an hour or two. I wouldn't stick any real wattage into it with the tuning capacitor in the link, there would be little sparking noises and the smell of melting plastic.
https://www.instructables.com/Medium-Wa ... op-antenn/
If you wanted to do real power you'd need an air spaced variable toast rack.

[Nige from Brum]

Ifn you're just looking to do your gaff then I would stick with the transmitter you got and make a resonant loop antenna to go with it. You could knock one up out of the junk box to see if it does what you want - keep you busy for an hour or two. I wouldn't stick any real wattage into it with the tuning capacitor in the link, there would be little sparking noises and the smell of melting plastic.
https://www.instructables.com/Medium-Wa ... op-antenn/
If you wanted to do real power you'd need an air spaced variable toast rack.

I tried that design a few years ago, but it didn't really work to well. I think it needed more capacitance than the transistor radio capacitor had. Also I think the turns are far to close together.

For MW DXing, mostly the dutch pirates, I use a 10 turn loop that is 50 cm per side and uses a dual gang variable cap from a vintage valve radio. The 10 turns are spaced a little over a quarter of an inch apart. It works from about 500 khz to about 1750 Khz.
The frame is just 2 pieces of pallet planking notched in the middle to form an X shape. Its not pretty, but it works extremely well.

You will see it at the end of this video

[outis]

Ifn you're just looking to do your gaff then I would stick with the transmitter you got and make a resonant loop antenna to go with it. You could knock one up out of the junk box to see if it does what you want - keep you busy for an hour or two. I wouldn't stick any real wattage into it with the tuning capacitor in the link, there would be little sparking noises and the smell of melting plastic.
https://www.instructables.com/Medium-Wa ... op-antenn/
If you wanted to do real power you'd need an air spaced variable toast rack.

Thanks, I had made a loop antenna sometime back - using enamel coil. I wasn't impressed with its performance and during a house move threw it away. This at the link you send me may prove to be better.
But the Carrier Current broadcasting cannot be that complicated or difficult. After all, small and cheap adapters are used for networking through the AC mains wiring. I have got a few myself, used for LAN anywhere in the house. I wonder if they might work with RF too...

[jvok]

Maybe worth taking apart a power line adapter and see what coupler they use. Component values might need changing for am but you could probably reuse the circuit topology

[Zozo]

My tuning coil was similar to yours, but was wound around a large jam jar, so it had a glass former!

Mine used a piece of white soil pipe and had maybe 80 turns with random taps all over the place. I remember back in the day it took me all night to make! I've still got it somewhere. Used it to load all kinds of wire antennas - I'd put a torch bulb and croc clip in series with the antenna and go through the taps until I got the brightest light - then attach the wire directly and crank it up!

Same here, I forget now how many turns or the total inductance; however I did find it better to drill holes through the pipe and then twist the tappings down to threaded posts along the bottom.

I use it mostly in an LC network to an Inverted L antenna which works really well with just a single earthing stake and counterpoise; but it can be used as an open aircore transformer.

SoilPipe-Inductor1.png

SoilPipe-Inductor2.png

[shuffy]

Same here, I forget now how many turns or the total inductance; however I did find it better to drill holes through the pipe and then twist the tappings down to threaded posts along the bottom.

Here's what's left of my effort. It's been in the garage for 20+ years, together with the remnants of whatever lashup I was last using. More turns than I remember, it looks to be around 120. The taps get progressively closer at one end of the coil. I never thought of the idea with the terminals at the bottom of the pipe, but as you can see, I've got quite a few taps.

soilpipe.jpg

I use it mostly in an LC network to an Inverted L antenna which works really well with just a single earthing stake and counterpoise; but it can be used as an open aircore transformer.

Zozo if you don't mind saying, what are your inverted L dimensions and what range are you getting for a given power with that earth? I tried a similar setup with around 15W and the performance was terrible - I think that's what the lashup with the capacitor will have been. Getting a decent earth is really hard.

[Zozo]

Same here, I forget now how many turns or the total inductance; however I did find it better to drill holes through the pipe and then twist the tappings down to threaded posts along the bottom.

Here's what's left of my effort. It's been in the garage for 20+ years, together with the remnants of whatever lashup I was last using. More turns than I remember, it looks to be around 120. The taps get progressively closer at one end of the coil. I never thought of the idea with the terminals at the bottom of the pipe, but as you can see, I've got quite a few taps.
soilpipe.jpg

I use it mostly in an LC network to an Inverted L antenna which works really well with just a single earthing stake and counterpoise; but it can be used as an open aircore transformer.

Zozo if you don't mind saying, what are your inverted L dimensions and what range are you getting for a given power with that earth? I tried a similar setup with around 15W and the performance was terrible - I think that's what the lashup with the capacitor will have been. Getting a decent earth is really hard.

I attempted to count the number of turns on my soil pipe inductor, which was not easy as I used self amalgamating tape to cover the whole thing; I estimated around 60 turns in total, so that’s at least half the amount compared to your’s. I also broke out the LCR to measure the total inductance, and for each tapping point which I’ve listed below.

TP1 = 178uH
TP2 = 139uH
TP3 = 92.5uH
TP4 = 52.7uH
TP5 = 20.9uH

inductance.png

For the capacitor I used a standard 365pf air space variable which I think came from an old Roberts radio. I set the capacitor to approximately ½ mesh, and using a twin needle PWR / SWR meter I hopped along the inductor tappings until I saw the best forward power to minimum reflected power. I finally adjusted the capacitor until I had the best forward to the minimum reflected on the meter.

The dimensions of my Inverted L has a just over a 20’ft vertical section starting from about 10’ft away from my house at ground level, which then goes up to a plastic insulator supported with paracord to the gutter of my property. The horizontal section is 30’ft that takes a slope towards the ground, which is then supported with another plastic insulator and paracord to a 6’ft fence post.

My earthing system is really less than ideal, however I make do with just the single earthing stake and mono counterpoise laying along the ground which is parallel to the horizontal section.

All-in-all the system I have works well for me and I can cover a reasonably wide area (4-5 km approximately) with just a simple QRP transmitter, In-fact this one in particular I posted some time ago here: viewtopic.php?t=3342

It may be worth noting that my location is just a little over 200’ft ASL, so this might be a very important factor to consider, and why my signal is able to propagate so well; A hilltop location that's overlooking towns and villages would be best. Although I’m at a reasonable height above sea-level, the terrain is a little up and down, so I don’t achieve a perfect omni signal in all directions.

But nevertheless we all just have to make-do and install the best compromise antenna system we can fit within the space available. Plus I don't like to push too much AM signal from my QTH, in the field is a different matter.

May I ask which TX are you using at present for your tests?

[shuffy]

Thanks for the detailed reply Zozo, I think I can visualise your setup pretty clearly now.

All-in-all the system I have works well for me and I can cover a reasonably wide area (4-5 km approximately) with just a simple QRP transmitter, In-fact this one in particular I posted some time ago here: viewtopic.php?t=3342

I've just looked at your other post, which I'd never seen before. Absolutely gobsmacked to see your Bias Comms boards!! You asked what my TX was, and actually it was numerous rigs but what I had in mind when I mentioned running 15W was the Bias Comms design published in various places in the 1990s. Looking at the circuit in your post, it's not the same. I'm not 100% sure if I built the design as published but I think it had some 2SK device or other, possibly a 2SK413, series modulated using a 2N3055. I could never get the mod to sound decent with that arrangement. A few years later, a friend built a larger variant with a pair of the FETs for the final. His rig sounded better than my earlier attempt, but he was running the PA at a higher voltage, so different choke and transformer designs. Anyway, I digress. He had his rig confiscated around 2004 if I remember right

May I ask which TX are you using at present for your tests?

At present, I'm not doing anything on MW. I have a FAT5 and the corresponding PWM board but it's currently tooled up for 49M. It sounds OK on air, but it's bulky and I feel I can improve on it so when I next get some time to play radio again, I'm moving to a different design. There won't be much of the FAT I can reuse so it might end up on the medium wave band and that's why I was curious about your antenna and earth. It's something I don't feel I've ever done justice.

As for the Bias 15W rig I'm sure I still have it, but it wasn't with the soil pipe coil. If I locate it I'll take another photo.

[Albert H]

A little MW rig (100mW) that's cheap and easy to build. The business end shown below uses a TL074 quad op-amp and three cheap transistors. It uses "carrier control" to reduce over modulation issues, and the ones I've built worked well into shortened wire aerials through a simple ATU.

The exciter part is the simple 3-chip synthesiser that's in other threads on this site (a 4046 for VCO and phase comparator, a 4060 with a 4608 kHz crystal for the 9 kHz reference, and a 40103 for the switch-set divider). The synthesiser works on +15V and the modulator / PA part uses +/-15V. You should be able to build the whole thing for just a few quid.

MW Driver.png

I'll put up a suggested PCB and a Veroboard version in the next few days. The ones I've lashed up have just been built "ugly" style on pieces of PCB material.

[Albert H]

The circuit above is based on one we came up with many years ago for "Panaxis" in the USA. It has the benefit of accepting a square wave drive signal (like that from a 4046 CMOS oscillator), and gives a reasonably clean sinewave out. If you really want to get picky, you can add a pi-filter to the output to further suppress the harmonic products, but we found that the harmonic outputs barely made it out of the box it was housed in!

In practical use, loaded through a tuning network into a shortened aerial, we found that the attainable range was entirely determined by the quietness of the channel it was on. On a quiet frequency, it could travel about 600m, but if the channel was noisy, you wouldn't hear it outside your own house. At just 100mW, it's not enough power to get you into trouble!

The circuit is slightly unusual in that it uses the diodes to modulate the square wave carrier. The tuned circuit has to be peaked to your frequency of choice, and one later version of the board had a combination of fixed capacitors selected by DIP switches and a couple of 65pF yellow trimmers, as we found that the price of the 110 - 450pF compression trimmer we used on the earliest ones rose to exceed the cost of all the rest of the parts put together!

We found that the easiest way to align the tuned circuit was to fully mesh the series trimmer, and get the most signal we could with the big trimmer, then slightly back off the coupling (series) trimmer to further peak the signal. We suggested the use of a receiver with an "S" meter or a simple passive field strength meter to peak the signal.

When you have the most carrier you can get, feed mod to the rig and adjust the 20kΩ trimmer resistor for the maximum undistorted audio. You'd then find that the AGC action of the modulator should compensate pretty effectively for various input levels fed to the rig.

The only other refinements we ever made to this circuit involved adding frequency response tweaks to the incoming audio, "brightening" the sound with some treble lift, and then rolling off the response at around 7 kHz. We also filtered the bass end slightly (roll off at about 25Hz) to prevent rumble from upsetting the AGC action.

[87to108]

Remember - the Yanks have a mains system that's just 55V either side of earth, whereas ours is much less forgiving!

Albert, that is incorrect, you are thinking about the output of the yellow building site 110V transformers which are indeed 55VAC to earth on each pole.

American homes have a 110-120V live ("hot" they call it) and Neutral (at or near earth potential) for most domestic appliances and lighting.

However for large fixed appliances like driers etc they have "240V" with two 120V in anti- phase (as well as the neutral if it is used). So the maximum voltage present to earth in a 240V appliance is 'just' 120V