A frequency agile 7 MHz FM exciter

People don't often build FM gear on HF. It takes up a wider bandwidth than SSB and is less efficient. But it is very simple. This video discusses how you can generate FM signals on 7 MHz with two transistors. 

PS: Find hints and tips for working DX in Minimum QRP. It's the top-selling manual on the equipment, antennas, operating and strategy of successful QRP operating. And its techniques work for 100 watts as well. It's available for under $US 5 each in electronic form. Or you can get a paperback version. Visit VK3YE Radio Books to find out more. 

Building a sliding variable capacitor

Have some spare kitchen foil and some plastic pipe? Why not make a sliding variable capacitor from it? This video shows how.

PS: Want to read more about antennas? Consider this selection of antenna books. They are affiliate links meaning that I receive a small commission (at no extra cost to you) if you decide to purchase.

    

Building a trap dipole for 7 and 14 MHz

I'm not a huge fan of trap dipoles. They work well enough but with room for only a few antennas I prefer to get several more bands out of them. Nevertheless if you're happy with a couple of bands then one can be a good project. And there's no antenna couplers to twiddle, unless you operate near the edge of the antenna's bandwidth. 

Anyway here's a video on one for 7 and 14 MHz to enjoy. I did it a few years ago but it continues to be popular. 

PS: Many other antenna topics are covered in Hand-carried QRP Antennas. Available in electronic and paperback form (some countries) this well-reviewed book is a popular read amongst hams who go portable.

Losing most of your signal: Tests with lossy coax cable

You might have a good transceiver and efficient antenna but station performance will be poor if your feedline is not up to scratch.

Here's a video where I attempt to measure loss with various lengths of RG58 at various frequencies with various pieces of test gear.

PS: Want to support The Daily Antenna? 

Please start your Amazon shopping here. 

You won't be charged extra and I'll get a small cut from any purchases you make (affiliate link). You can buy lots of stuff there, including electronic parts and my books.

28 & 50 MHz portable dipole

We've had this one before but if you don't have one now is a good time to build one.

Here in the southern hemisphere we're approaching our peak time for sporadic-E propagation.

Both 10 & 6m will produce long distance contacts and strong signals.

Even a simple dipole like this is good for many enjoyable contacts.

PS: Find hints and tips for working DX in Minimum QRP. It's the top-selling manual on the equipment, antennas, operating and strategy of successful QRP operating. And its techniques work for 100 watts as well. It's available for under $US 5 each in electronic form. Or you can get a paperback version. Visit VK3YE Radio Books to find out more. 

Light pole antenna and crystal set (video)

At mentioned yesterday I've been doing experiments with a light pole antenna and a crystal set.

Here's the video arising from it.

The audio is from holding the headphones up to the camera with no amplification.

In practice it's much louder than you'd here on the video.

PS: I've now written six books on various aspects of amateur radio. Whether you experiment with antennas, enjoy QRP or are starting out in radio there's a book for you. Find out more here.

More light pole antenna tests (with a crystal set)

OK so maybe some are still skeptical about my light pole antenna tests on 160m. I won't say much here as a video is coming soon but they also work really well as a receiving antenna on the AM broadcast band. How do I know? I used it with a crystal set and got great volume into unamplified headphones. 

The proviso is that impedance matching must be excellent. You can't just hook the 20m perimeter loop to the crystal set's antenna and earth terminals and expect good results. I used my loop antenna coupler. Tuning is a bit finnicky with its controls also selecting the station in conjunction with the crystal set's tuning capacitor but it does make a big difference. My coupler only goes down to about 1100 or 1200 kHz but the strongest station on 1377 kHz comes in well as do some others. 

Anyway the results were excellent so look out for the video. 

PS: Many other antenna topics are covered in Hand-carried QRP Antennas. Available in electronic and paperback form (some countries) this well-reviewed book is a popular read amongst hams who go portable.

How long can an FT817 operate with 8 x AA NiMH batteries?

I normally use external batteries with my FT817.

Those supplied in the Yaesu battery pack were only 600 mAH.

And even those in the FT818's pack have a bit more capacity but not quite enough.

Anyway the video here documents my experiences with 8 NIMH batteries purchased from IKEA.

They're low self discharge rechargeables.

PS: Want to read about antennas? Consider this selection of antenna books. They are affiliate links meaning that I receive a small commission (at no extra cost to you) if you decide to purchase.

    

Filing ceramic resonators

Ceramic resonators are handy parts for the radio tinkerer. They can be shifted in frequency much more than crystals by adding series capacitance and/or inductance.

Here's an attempt to shift frequency by other means - by filing. These two videos describe how I did it.

PS: Want to read more about antennas? Consider this selection of antenna books. They are affiliate links meaning that I receive a small commission (at no extra cost to you) if you decide to purchase.

    

What you're most interested in

A housekeeping type post. What topics are Daily Antenna readers most interested in?

The answer's pretty clear. Many of you are QRPers interested in new gear. My thoughts on the IC705 got almost twice the viewership of any other item.

Antennas feature prominently because for a while that was the only topic covered here. Those for small spaces are very popular. For example apartment HF antennas and magnetic loops. Maybe it's because you're more likely to be on the web than on the air if your antennas are limited?

There's also a fair interest in VHF/UHF antennas. Three of the top 10 posts are in this category.

Anyway you can see all the top 10 below. It will help me think of things to write about.

PS: I've now written six books on various aspects of amateur radio. Whether you experiment with antennas, enjoy QRP or are starting out in radio there's a book for you. Find out more here.

Bidrectional wire beams - tests on 28 MHz

Further to yesterday's post, here's a video of a test I did with signals from a local beacon on 28 MHz. I compared a vertical dipole on its own with a 2 element beam, firstly with a reflect then with a director. Watch the video to hear the comparison. 

PS: Want to read more about antennas? Consider this selection of antenna books. They are affiliate links meaning that I receive a small commission (at no extra cost to you) if you decide to purchase.

    

Bidirectional 2 element beams with an electrically shortened and lengthened parasitic element

One of the cheapest ways of getting some gain with a wire dipole antenna is to put a parasitic element about 0.15 to 0.2 wavelength in front or behind it. 

If the parasitic element is about 5% longer and put behind the driven element it becomes a reflector. If it's 5% shorter and put in front of the driven element it becomes a director. 

What about if you wanted to flip the beam direction by 180 degrees?

One approach is to use a parasitic element that when shortened becomes a director for one direction and if lengthened becomes a reflector. The position of the parasitic element can then stay the same for both directions. 

How do you easily lengthen and shorten this element? 

You don't actually need to physically change its length. Electrically changing it will do. 

How do you do this? 

You could start with an element that's 5% smaller than the driven element. That makes it a director. But if you put an inductor in its middle it's electrically lengthened to become a reflector. A switch across the inductor lets you choose whether you want the inductor or not and thus your antenna's favoured direction.  

How much inductance do you need to make your wire beam bidirectional? 

I can't recall reading much about it. But I did see this description by M0MCX of a 7 MHz switchable direction wire yagi. That used a 2uH inductor in the middle to make a director a reflector. 

Scaling it up means you need about 0.5uH for 28 MHz. I also put the inductance and the desired frequency into a reactance calculator. The inductance has a reactance of about 89 ohms. 

I also came across this single mast wire beam for 14 MHz. This used capacitors in the middle of elements instead of inductors. In this case all elements are the same length since all were potentially driven elements.

But if you put a capacitor in the middle of one you make it a director. The capacitance specified was 235 pF.  The calculated reactance was about 47 ohm. But note that as you're starting with something of driven element size you are only electrically changing its length half as much as if you started with a reflector. If you were doing that on 14 MHz you'd be aiming for around double (~90 ohm) reactance. In other words around 120 pF capacitance. 

Anyway I thought I should write about this as this technique is possibly not discussed as much as it should. And I might do some experiments and put up a video soon. 

PS: Many other antenna topics are covered in Hand-carried QRP Antennas. Available in electronic and paperback form (some countries) this well-reviewed book is a popular read amongst hams who go portable.

More hamfest bargains

Yesterday I went to the Rosebud Radio Fest - one of our local hamfests. Here's what I got.

PS: Heard about my new book? It's Australia's own amateur radio handbook. Available in both electronic and paperback form, you can find out more here. 

Importance of inspecting and maintaining antennas

Haven't inspected or done antenna maintenance for a while? Where why you should!

PS: Want to read more about antennas? Consider this selection of antenna books. They are affiliate links meaning that I receive a small commission (at no extra cost to you) if you decide to purchase.

    

Pedestrian mobile presentation (Club talk)

No time to write a post today as I'm working on a club presentation for tomorrow.

So today I'll bring you a video of one I did a few years back to one of the big clubs in Melbourne (EMDRC).

PS: Heard about my new book? It's Australia's own amateur radio handbook. Available in both electronic and paperback form, you can find out more here. 

A dualband tuned circuit switching trick

Something I haven't yet built but have been thinking about. It's a simple front-end tuned circuit for a simple 80 and 40 metre receiver. I wanted just one inductor (actually a pre-wound RF choke) and easy band switching.

3.5 and 7 MHz are harmonically related. As a rough rule of thumb 10 uH requires 200 pF to resonate there. If you wanted to preserve the LC ratio then you'd use 100pF to resonate with 4.7 uH on 7 MHz. In other words double the frequency, halve both values.

What if you wanted to leave the 10 uH in and bring it to resonance on both bands? Then instead of doubling (or dividing by two) you'd need to multiply the capacitance by 4 (or divide by two). You can get away with this for adjacent bands but not if they were too far apart (eg a frequency ratio of 3 or more to 1).

In the case of 3.5 MHz and 10 uH you still need your 200 pF. For 7 MHz though as you're keeping the inductance the same you need a quarter the capacitance. That is 50 pF. If you only have 100 pF capacitors below is a possible scheme using a double pole double throw switch.

It took a little while to work out on paper. As you see it the tuned circuit is set to 7 MHz. You can tell that because the 100 pF capacitors are in series, giving 50 pF. Flick the switch the other way and the capacitors are in parallel, giving 200 pF. 

This requires a double pole double throw switch. These may be more expensive than a single pole double throw or single pole single throw switch. If the latter type is all you have then you'll need to do something else. For example you could have a 47 pF capacitor permanently in the circuit to give a 7 MHz resonance. A 150 pF in parallel could be switched in for 3.5 MHz. 

Another approach could have two capacitors in series (to give the lower capacitance) and a switch to short one of them to give the higher capacitance for 3.5 MHz. That's harder to work out (you'll need to use an online calculator like this) but 180 in series with 68 pF will give 50 pF with no switch. Then if you short out the 68 pF you will get 180 pF for 3.5 MHz. If it's not quite enough then you might put 18 or 22 pF in parallel with the 180 pF (that will slightly but not very much raise the 50 pF mentioned before). 

PS: Want to read more about antennas? Consider this selection of antenna books. They are affiliate links meaning that I receive a small commission (at no extra cost to you) if you decide to purchase.

    

More 28m light pole antenna experiments

Some more 160m AM with the 28m light pole. This time I use the FT817 which has a 50 ohm antenna connection. I use the loop tuner featured here between the feed loop and the transceiver. 

Later on I try some midday WSPR, comparing 160 and 80m with a station 31km away. 

PS: Heard about my new book? It's Australia's own amateur radio handbook. Available in both electronic and paperback form, you can find out more here. 

28 metre light pole - this time as an antenna on 3.5 MHz

My video from last week showing a 28 metre light pole being coupled into to operate as an antenna on 1.8 MHz was hugely popular with 12 000 views to date. 

A couple of days ago I was out again trying it on 3.5 MHz. This time I did a test with the feed loop moved away to the pole to see what would happen to signals. Though conditions were varying the pole appeared to have an effect. 

Watch what I did in the video below.  

There are definitely refinements needed. For example the VSWR is showing somewhat high so further work is needed (beyond the L-match network) if using it with a transceiver with a 50 ohm output. 

A thing you should be aware of is the different antenna requirements for 160m and 80m. A major propagation mode on 160m is ground wave for contacts within about 100km. That needs a vertical antenna. Whereas on 80m and higher frequency bands the ground wave is less but skywave becomes more important. That requires a high angle radiator such as a low dipole. A vertical may not necessarily be the best type of antenna. So although the 28m pole looks impressive you actually might get better results if you were to use the 9m squid pole as a support for an inverted vee dipole or end-fed. But the vertical has potential for DX contacts which need a low radiation angle. 

PS: I've now written six books on various aspects of amateur radio. Whether you experiment with antennas, enjoy QRP or are starting out in radio there's a book for you. Find out more here.

RF actuated LED tx indicator for QRP rigs

A simple little add-on for homebrew or kit QRP rigs that don't necessarily come with much metering. It's only a few parts and very cheap. Here I'm using it with a uBitx.

PS: Find hints and tips for working DX in Minimum QRP. It's the top-selling manual on the equipment, antennas, operating and strategy of successful QRP operating. And its techniques work for 100 watts as well. It's available for under $US 5 each in electronic form. Or you can get a paperback version. Visit VK3YE Radio Books to find out more. 

Amateur radio on groups.io

Amateurs often share ideas on Facebook groups or forums like QRZ or eHam. But there's another place where you can find discussion, especially on more specialised facets.

These are email groups (although you can also read them via your browser). The most well known is Yahoo Groups. However this has been scaling down and many amateur groups have gone over to groups.io.

Use the search in the top right to find groups of interest to you.

Here's just a few linked examples.

Amateur radio
Antennas
DX
Elecraft
QRP
VHF radio

Anyway you get the idea. Try searching your amateur radio interests and see what you get.

Some groups have their messages viewable by anyone while others require you to join.

PS: I've now written six books on various aspects of amateur radio. Whether you experiment with antennas, enjoy QRP or are starting out in radio there's a book for you. Find out more here.

You Want DX? I'll show you in four easy steps (M0MCX video)

Here's another British video.  Unlike yesterday's this one was made just a few hours ago. By Callum M0MCX it's about DXing for beginners. It takes aim at the naysayers who say there's none around and gives some tips on how you can work your share. 

PS: Another place you can find hints and tips for working DX is Minimum QRP. It's the top-selling manual on the equipment, antennas, operating and strategy of successful QRP operating. And its techniques work for 100 watts as well. It's available for under $US 5 each in electronic form. Or you can get a paperback version. Visit VK3YE Radio Books to find out more. 

Dud Charman's Aerial Circus

Before YouTube few hams made videos. Even if you did the audience would be limited. Video media was not cheap and sharing involved making a copy and posting a tape. Radio clubs sometimes had video presentations. Here in Australia the WIA had a videotape library that clubs could borrow videos from. Amateur television operators also often replayed videos via their repeaters. 

One of the famous videos from that era was Dud Charman's Aerial Circus. It's a 1970s lecture to a UK radio club. It had views worldwide in the ensuing decades. Here it is on YouTube for a new generation of hams. With practical demonstrations it shows how antennas really work. It's an hour long but well worth watching. 

PS: Want to read more about antennas? Consider this selection of antenna books. They are affiliate links meaning that I receive a small commission (at no extra cost to you) if you decide to purchase.

    

New 'Radio Adventures' video series from SOTA Beams

Richard G3CWI of SOTABeams fame has launched what is planned to be a regular video series. 

The first Radio Advantures discusses binaural reception. Here's the video. You need to use stereo headphones to hear the effect.

Looks like a series worth subscribing to.

PS: Want to support The Daily Antenna? Please start your Amazon shopping here. You won't be charged extra and I'll get a small cut from any purchases you make (affiliate link). You can buy lots of stuff there, including electronic parts and my books.

Loading up a tall light pole for a quick and easy 160 metre antenna

This started as a quick experiment but turned out into something that I think will change the way I do 160 metres AM portable. All you need is a large metal light pole. Such as you see around sports ovals.  

The idea is you use a telescoping pole to install a coupling loop of wire right next to it. Then you seek to load it up. With any luck the tall mast will be part of the antenna. Well that was my result anyway. 

The outcome was a very simple 160 metre antenna that can be set up very quickly. And you don't need to lay out ground radials. More in this new video.

Audio recorded by VK3CSJ

Ground tuning unit referred to above

Have you tried something like this and what were the results? Please share your experiences in the comments below. 

PS: Into low power amateur radio? Minimum QRP is the top-selling manual on the equipment, antennas, operating and strategy of successful QRP operating. It's available for under $US 5 each in electronic form. Or you can get a paperback version. Visit VK3YE Radio Books to find out more. 

Melbourne Cup Day - 160m AM activity

Today was Melbourne Cup Day. A public holiday. We're possibly the only place in the world to have a public holiday for a horse race. But it provides an opportunity for people to get onto 160 metres AM. Which has become a bit of a tradition here with a higher than normal number of portable stations on the air. 

These are some videos of activity over various Melbourne Cup days. 

2008

2010

2016

2017

What 160m AM did I do today? Quite a bit. More in a future post. 

PS: Heard about my new book? It's Australia's own amateur radio handbook. Available in both electronic and paperback form, you can find out more here. 

Sights and Sounds from Melbourne QRP by the Bay

A video review of Saturday's Melbourne QRP by the Bay. Weather forecast was poor but it got better towards the end. And some great examples of homebrew on show. Including a small but high powered AM transmitter from Wayne VK3ALK and Paul VK3HN's excellent portable HF SSB transceiver. And we tried some cheap 27 MHz gear. 

Wish to hold your own similar QRP gathering? Here's some tips:

PS: I've now written six books on various aspects of amateur radio. Whether you experiment with antennas, enjoy QRP or are starting out in radio there's a book for you. Find out more here.

Regen receiver with no tapped coils or secondary windings

Most regen receiver circuits use the coil as part of the path to provide positive feedback that is required to deliver the high gain that this configuration is famous for. And to allow reception of SSB and CW signals. This is either done by tapping the coil (often the source in a FET design is connected to the coil tap) or with a second, smaller winding. One side of this usually goes to the drain (if a FET design) or collector (if a BJT design). 

However, just like VFO circuits it's possible to not have a tapped coil and use capacitors instead. Such as with this Tandy/Radioshack receiver kit. Also see here for the instructions (it's a 3 transistor shortwave regen).

I knocked one up and got it to oscillate. Not only that but I could hear amateur SSB signals on 7 MHz. It wasn't stable but this was due to my open-air test design with no shielding. Anyway if you're after a simple regen I suggest you try this type. My coil was about 20 or 30 turns over a T50-2 toroid. And the variable capacitor? Approx 10 - 200pF. 

My unit just has a single transistor detector directly driving a TL431 (discussed yesterday). That has enough gain to directly drive a speaker on ham signals. If you build one please let me know your experiences in the comments below. 

PS: Interested in antennas? Consider this selection of antenna books. They are affiliate links meaning that I receive a small commission (at no extra cost to you) if you decide to purchase.