Archive for the ‘antenna’ Category
The Grand Illusion
February 28th, 2016 | 
Author: Five by Nine... QRP... How can it be?
What does an S-Unit really mean and how can a QRP station sound like a 500w station?
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| The real gain doesn't come from transmitter watts |
I rarely go up to the phone portion of the bands. Since I started doing QRP and CW last summer I think I've only made two SSB contacts just because my focus has been CW. But last night I was working on a bench project and tuned the Elecraft KX3 up to the phone portion of 40m for some entertainment.
A station in Rhode Island was testing his amp with a new antenna and was getting reports from various stateside operators. There was a lull where no one was answering his CQ so I thought I'd give him a call. He was peaking at S9 on my KX3's meter and he also sent me a signal report of S9 with some 10 over peaks. I then told him I was a QRP station running 10 watts and heard the usual surprised reaction from a QRO station.
I gave him reports as he switched back and forth from running barefoot ~75w to his amp ~500w. With his amp on he was an S9, running barefoot he was S8. So the amp gave him one additional S unit. In terms of hearing him I would have been hard pressed to tell much difference simply by volume. He was perfectly copyable without noise with the amp off.
We also did some tests with my station at reduced power (as if...) At 10w-12w output I received a S9 to S9+10. Reducing output to 5 watts netted me a S8 report and when I reduced to 1 watt (one watt) he was still able to comfortably copy me and I received an S5. So with my station at 1 watt and his running 500 watts we could still converse via SSB. Ladies and Gentlemen you don't need as much output wattage as you think you do.
He was running through a newly constructed homebrewed vertical while I was using my 80m OCF Dipole. We didn't discuss what sort of radial system he had installed, but the difference in antennas was likely the deciding difference in our stations. We were about 500 miles apart and his vertical probably had more low-takeoff gain than my dipole, or possibly more ground loss so I probably had better high angle gain on him for the short 500 mile skip. I think the take-away from this exercise is that the antenna is generally the key rather than transmitter power. If I can get 6 dB of gain from my antenna I have in essence quadrupled my effective radiated power. Quadrupled? Yes, Quadrupled effective output power.
Power and S-Units
You've probably heard it before but it's worth a refresher... Our radio's meter display a measurement in "S-Unit". To move the meter up one S-Unit the receiver must hear 6 more dB (decibels). So one S-Unit is 6 dB.
A decibel is:
- A Power Ratio: dB = 10 Log P2/P1
- A Voltage Ratio: dB = 20 Log V2/V1
You increase 3dB each time you DOUBLE your power
That's worth repeating...
You increase 3dB each time you DOUBLE your power. So to gain one S-Unit you must quadruple your power.
So if you are running 100 watts, to gain one S-Unit using the same antenna system you must increase your power to 400 watts. If you are running QRP SSB (10 watts) that is only 1.5 S-Units down from 100 watts. 100w / 2 (-3dB) = 50w / 2 (another -3dB or 1 S-Unit) = 25w... etc.
We have a great hobby, but there are so many aspects of it that sound like common sense when they really are not... like increase your power.
Increasing power gains you very little compared to a better antenna systems. Put that in your 811A amplifier tube and smoke it !
That's all for now.
So lower your power and raise your expectations (or your antennas)
72/73 (Note: 72 is a common substitute for 73 among QRPers... as in "not enough power for 73")
Richard, N4PBQ
Antennas offer the cheapest increase in dB
Note the statement above "using the same antenna system". That's the key then isn't it? It's easier to get 6 dB of gain from an antenna than from wattage. A 40m doublet can offer significant directional gain especially when operated on higher bands. Now unless it's rotatable you will be at the mercy of the directionality of its lobes but if you have trees or tall structures you can very cheaply string up a few dipoles oriented in different directions and for far less money that a 500 watt amp (6 dB). If you can only have one wire antenna you may miss out on some DX in the antenna's nulls but you will have some stellar gain in the direction of the lobes. Of course rotatable yagis and beams are the best but now we are talking about real money again. I'm talking bang for the penny. You don't have to buy a wire antenna. Some Dacron rope or weed-eater line and some surplus insulated wire is all you need. You can even make your own feedline cheaply from electric fence wire and insulators.We have a great hobby, but there are so many aspects of it that sound like common sense when they really are not... like increase your power.
Increasing power gains you very little compared to a better antenna systems. Put that in your 811A amplifier tube and smoke it !
That's all for now.
So lower your power and raise your expectations (or your antennas)
72/73 (Note: 72 is a common substitute for 73 among QRPers... as in "not enough power for 73")
Richard, N4PBQ
Get a taste of the RF coming and going
Elecraft CP1 - A tasty RF treat
I had some time this afternoon to assemble another Elecraft mini-module kit. This time it was the Elecraft CP1 directional coupler.
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| Elecraft CP1 Kit |
Couple what?
Ah, so if your new to this like me you might be asking what does a coupler do? Well it sorta listens in on the signal going out (forward) and reflected (back) and is able to send an attenuated sample of the signal to other devices. It attenuates the sample by either 20db or 30db depending on how you build the kit.The 20db version is good for signals 25 watts and less so that's the way I built it. It was easy to build but my glue under the second toroid wasn't strong enough and you can see it popped up a bit. Also the Elecraft instructions had one confusing instruction concerning mounting the toroids. The instructions say "... When wound and mounted correctly, the enamel wire will emerge from the top of each core and connect to the top hole at each inductor location". Well when you wind a toroid only one of the wires can "emerge from the top of the core" while the other comes from underneath. This confused me for a minute until I finally just went on with the install. Anyway, if you're a stickler for following instructions that one may cause a moment of pause...
The switches for the two outputs forward, reflected (J3, J4) are in the up position when they are not in use. When the switch(es) are in the up position the 50 ohm 3 watt resistor(s) take the place of the switched off output. Don't disconnect an output and leave the switch in the bottom position. I'm not sure what will happen... maybe nothing, probably a bit of a mismatch on the SWR, or maybe it could be like "Crossing the streams" in Ghostbusters. Your mileage may vary.
My uses for a coupler
My old Ten-Tec Century 21 has an analog VFO dial that gives me a good guess at where I'm at but I use an external frequency counter to give me more information. I had it sorta rigged my frequency counter to sample the signal from RF leaked on the shield but I didn't really know how much power I was sending to the counter so this coupler allows it, as well as other devices, to be safely connected to the transmitted signal.I also plan to use the coupler for IMD tests using a oscilloscope and other projects. It's handy device to have in your collection.
My confusion
I will admit I am still such an idiot when it comes to understanding how this stuff works. After I built it I was testing continuity and saw that input/output (J1, J2) both showed a short from ground to center pin on both BNC connectors. I thought I'd mis-soldered something and spent the next two hours unsoldering components and trying to trace the fault...
There was no fault. The way this thing works is a bit of mystery to me but as best I can tell it simply reverses the phase of the signal coming in one side (J1) and leaving the other (J2) and as far as continuity tests go, EVERYTHING has almost zero impedance. I'm still bewildered but it's AC not DC so my continuity tests don't mean much.
But in the end - It works
I finally just resoldered it, scratched my head and thought I'd give it a try. I connected the coupler between my radio and a dummy load and transmitted a watt and noted that the SWR on the radio was fine. Then I hooked up my frequency counter and it worked like a charm sending an attenuated signal to J3 for the frequency counter.
My MFJ watt meter doesn't seem to be all that accurate but I did a power test with it both in-line and absent. My MFJ watt meter measures 300w / 30w so it isn't very accurate at QRP levels. But I noted a slight difference in power reported when the coupler was in-line. If I had to guess by "Mark-One-Eyeball" I'd say the coupler was stealing about 1/2 watt. Maybe a bit more so that's something to consider. I'll know better once I build my Elecraft watt meter since it's accurate down to a tenth of a watt.
That's all for now
So lower your power and raise your expectations
72/73
Richard, N4PBQ
Antenna faulty
It looks like my tri-band Par antenna, which should be a good match on 10m, 20m and 40m is faulty. It is a good match on 10m, but only on 20m and 40m via the ATU. Tomorrow I shall try loading it up as a long wire tuned against ground via the ATU. Somewhere I have a Sandpiper Poliakov vertical that I should erect. As I recall this has a 9:1 unun so it matches well on most HF bands via an ATU.
Even soldering on a coax is hard work these days! Oh to be fit.
At the moment I am on 630m WSPR using the earth-electrode “antenna”.
Can anybody hear me
Calling QRP CQ - Inconceivable
My 80m OCF Dipole has been a surprisingly good antenna and I've made contacts with it on all bands except 6m and 160m. Based on my past experience trying to tune up short antennas on 160m I really hadn't considered trying to use this Windom for 160m. But through some email exchanges with another ham in Illinois who had recently put up a 160m antenna we decided to try a scheduled QSO on the top band. So it was time to give the Windom a shot on 160m.
Amazingly my 80m Windom / OCF Dipole has 4.5:1 SWR native around 1.8 mHz and it matches easily with a tuner across the entire 160m band. That was a surprise.
Amazingly my 80m Windom / OCF Dipole has 4.5:1 SWR native around 1.8 mHz and it matches easily with a tuner across the entire 160m band. That was a surprise.
I tossed my mighty 5 watts call out at 1810 kHz not expecting much...
Within a minute of calling CQ I had a faint QRP station from Maine tried to work me. After about 4 tries I finally copied his call correctly but then lost him. Immediately another station called me and we exchanged the niceties of signal reports, location, rigs and weather. I received a nice 579 report for my 5w and I gave him a 599+ report for his thundering kilowatt station. He needed to work my County so I was glad to be able to provide him with the contact. Following that call the former QRP station from Maine was back in there and finally we worked each other. We had a nice QRP to QRP QSO on the top band. He gave me a 549 report but he was using a 400 ft beverage receive antenna. I was struggling a bit more to copy him through local QRM on my side and a less qualified receive antenna and reported his signal as 339.
Those were my first two contacts on 160m using CW. Who'd have thought my cloud burner antenna and QRP power would get me such quick results on the top band. I just figured no one would hear me.
So how do you know if and where your signal is getting out ?
The Reverse Beacon Network
I had to quit right after those two QSOs but when I later checked my email the original station with whom I'd planned the scheduled QSO reported that although he had not heard me he said I was getting out and sent me a link to something called the reverse beacon net showing a couple of stations that were hearing me on 1810 kHz.
You mean I can find out in near realtime if and where my signal is being heard by an automated system? No way! That is cooler than a Ronco Pocket Fisherman. Recall that I'm relatively new at this stuff and this may be old hat for a lot of you. But the ability to toss out your call and in real-time check where your signal is getting to just warms the push-pull final transistor in my heart.
The Reverse Beacon Network can give you the last 100 reports of your station. So I took a look and saw some of my weekend activity where I was shooting some fish in a barrel (I mean working contest stations) and there were beacon reports of my call from such places as far South as the Antilles and as far West as Utah.
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| Map of the last 100 reports from Reverse Beacon stations of my call sign Color coded by band |
So the reverse beacon network report tells you what station heard you, the frequency, the signal to noise ratio (higher is better) and your word per minute (wpm) speed.
It even includes a speedometer
Being a new CW dude my word per minute speed is of interest to me. Most of my QSOs in the past week have been at 15-16 wpm. I'm using a Vibroplex Bug I received last weekend and have slowed it down with a home-made weight attached to a drywall anchor pressed on the end of the pendulum. I found it interesting that some beacon stations reported me at 19-23 wpm. I looked at the time and the frequency and realized that the higher speed was from my first on-air QSO using the Vibroplex Bug with N4HAY before I slowed it down with my junk box bug tamer.
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| My brief speed key session with N4HAY |
So if you are using a manual key and don't know what speed you are sending just check out a beacon to see what speed they are reporting.
Summary
This reverse beacon stuff has been around a while. So unless you're a newbie like me you probably already knew about it. But if you haven't used before it's very cool, especially with regard to knowing how your QRP station is being heard. Are you making it 1000 mile per watt? Is your antenna propagating East, West, North or South. How and where is the skip? This answers many questions that I had been wondering about as I'm operating. A shiny new toy, just in time for Christmas
So that's all for now.
So lower your power and raise your expectations
73/72
Richard N4PBQ
New antenna
My shack is fairly spartan. Just the IC7000 as a main rig. The antenna farm is equally so with all antennas in the loft bar a 2m & 70cm colinear.
Its a fairly spacious loft mind you. Enough room for a Watson 80 plus 2 dipole (Which they don’t seem to make any more) with extra elements for 30m and a 4 element 10m band yagi. But 80m is really not working for me.
So with a few hours to spare this weekend and a bit if ladder line I pulled together a W3EDP antenna. Its nothing new and a very cost effective antenna. So without going through all the detail it was either that or nothing at all for 80m. I just simply don’t have the space for a windom ( which is what I would have preferred) and G7FEK limited space antenna would have meant more stuff in the garden to annoy the XYL.
Needless to say I got the chance to try it out, firstly with the Hack Green SDR and shortly afterwards a nice QSO with Peter, G4LHI in Huntingdon.
So for a couple of hours work I can recommend the W3EDP. Noting of course the current at the end and need for a good counterpoise / earth. I can also say that even in a lash up configuration it withstood some pretty big winds here in IO84 this weekend.
So where to find out more:
Well a simple Google will give you most of the info you need but you could do worse than invest in the the Stealth Antennas book. I have a copy of the older version,
I see the new one has a different cover, I’m not sure if there was much change in the insides between editions but there’s something in there for everyone. From ultra small weird looking things to some old favourites like loops and verticals all the way to ultra cheapo types.
Its not all good news though. The XYL isn’t happy with the wire. The Watson 80 plus 2 (whose inspiration came from the G4ILO section of this book) didn’t quite meet my expectations and I didn’t quite get the G7FEK constructed. Maybe next time.
If you’re stealthier on 80m then I’m sure I won’t be the only one who is interested in finding out how you did it. If not then lucky you for having enough garden and don’t forget to listen out for the weak signals. 
Ham Radio & PLT devices
In recent stories I have heard audio samples and read stories of how these devices can create S9+20db of noise. Thus reducing the amateur bands unusable.
I wanted to see for myself the effect of using PLT devices in my property. So I visited PC World and purchased 2 devices from NetGear. The Powerline 500 promise 500Mbit/s and this would solve a huge problem I have in my home right now, but feared for what it would do to my beloved radio.
The results were interesting and nothing what I expected. You can see my full test in the video below – but for a spoiler alert keep reading....
The results were - It did nothing. It had zero effect on any of the bands I use at home. After the video I monitored the shortwave bands and tried other frequencies. Again, nothing. I tried it while the network was busy - I streamed 4K films and copied a 25Gb file. Guess what. Nothing.
The moral ? – Don’t believe the hype.
Ham Radio & PLT devices
In recent stories I have heard audio samples and read stories of how these devices can create S9+20db of noise. Thus reducing the amateur bands unusable.
I wanted to see for myself the effect of using PLT devices in my property. So I visited PC World and purchased 2 devices from NetGear. The Powerline 500 promise 500Mbit/s and this would solve a huge problem I have in my home right now, but feared for what it would do to my beloved radio.
The results were interesting and nothing what I expected. You can see my full test in the video below – but for a spoiler alert keep reading....
The results were - It did nothing. It had zero effect on any of the bands I use at home. After the video I monitored the shortwave bands and tried other frequencies. Again, nothing. I tried it while the network was busy - I streamed 4K films and copied a 25Gb file. Guess what. Nothing.
The moral ? – Don’t believe the hype.
