Archive for the ‘antenna’ Category

LHS Episode #164: Ancient Antenna Modeling

AncientAntennaModelingWe're done with the editing of Episode #164 and here it is for your listening pleasure. In this episode, your hosts tackle topics from Bugbook computers to permanent amateur radio licenses, from Turing phones to Raspberry Pi computers and from antenna modeling software to lobster on pizza. We hope everyone will find something to enjoy. Please let us know by sending us feedback. We'd love to hear from you.

73 de The LHS Crew

I will have a BLT please

The BLT-Plus Balanced line QRP tuner

I was looking for a QRP tuner for the 1Watter 40m transceiver I am building that would work with both balanced feedline antennas as well as coax feedline.  The traditional Z-Match tuner is quite efficient at tuning balanced line antennas and the built-in SWR bridge gives you an all-in-one tuner and SWR indicator without having to take a separate SWR meter along with its inherent mess of cabling a separate SWR meter.  The BLT in the name stands for "Balanced Line Tuner".

This tuner kit is available from the fine folks at Pacific Antenna
The Kit as it comes out of the bag

The kit comes with everything you need except for hookup wire and your soldering equipment. Instructions are downloaded from the qrpkits website.

Why use a z-match ?


Here are some advantages that the Z-match design offers:
  • Matches balanced loads without the use of lossy baluns.
  • Being a parallel resonant circuit, the Z-match can provide some band-pass filtering for your receiver and harmonic attenuation for your transmitter.
  • A well-designed Z-match tuner has a high Q and is more efficient (less lossy) than other types of tuners.
  • The fixed inductor simplifies construction (no taps or rollers needed).

The secret sauce

Matching balanced line fed antennas is sometimes problematic for a traditional balun and tuner as the antenna can present impedances that are far outside of the balun's design.  The Z-Match uses a center tapped coil to keep the complex impedance balanced across the inductor (at least that's how I understand it).  I have measured my Elecraft BL2 balun getting appreciably warm at QRP levels when connected to my doublet indicating loss I'd prefer to avoid.  The Z-Match design supposedly results in less loss.

Built in SWR indicator

The BLT plus includes a Dan Tayloe N7VE LED SWR indicator which eliminates the need to carry a separate SWR meter.  The concept is beautiful. The SWR bridge is switched into "Tune" mode and presents a 50 Ohm impedance to your transmitter while you are tuning so that you don't risk damaging sensitive home-brew finals.  The LED lights when the SWR is too high and dims and then goes out as the match is made.  It is simple and fast to use.   The instructions for the bridge are not with the BLT instructions. Download them from this link.

SWR bridge with LED indicator


Switch to Tune to present a low SWR to the transmitter while matching, switch to Operate when finished

Building

The kit is relatively easy to build with one tapped toroid to wind for the SWR bridge and one 3 winding toroid for the tuner.  I faced a few issues that you might avoid:
  • The kit is provided with really nice water slide decals that give it a commercial look (if you don't ruin them like I did).  The instructions recommend applying a clear coat to the decals after they are applied.  I used a Krylon matte finish clear coat which indicated it was fine for metals and plastics but it partially melted the decals and caused them to bubble.  I'd suggest testing whatever you are going to clear coat them with first.
  • Don't over tighten the plastic tuner shafts or you won't be able to slide the knobs on (yes I did).
  • The binding posts have little plastic spacers that separate and it isn't obvious.  If you install them and wonder how they don't ground themselves (like I did) you've done it wrong and will have to go back after it's together and try to remove them with all the wiring in place.
  • The bolts for the binding posts are very soft metal and the nuts can strip them if you apply too much force (yep I did that too).
  • The main toroid has three sets of windings and they overlap.  Pay attention to the instructions about winding them all in the same manner (clockwise or counter clockwise) or you will have to rewind them (yep, I did that too).
  • The 3 windings on the main toroid overlap so you won't be able to go back and verify your turns when doing the 2nd and 3rd winding so count carefully (ask me how I know).
  • Temporarily attach the SWR bridge to the front panel to get the spacing correct to solder the LED leads.
The SWR bridge instructions are separate from the kit instructions and simply googling them will give you instructions for an older version.  Use the version here.

My tuner toroid ended up being a bit messier than I'd like because I had to rewind it and my resulting leads aren't as short as they could be.  I may go back and trim the leads to make it tidier but my least favorite part of winding toroids is heat stripping the insulated magnet wire so I'll probably leave it as is.  Initial tests indicate it's working great.

My messy toroid winding... but it's working fine

Operation

  1. Connect your transmitter and antenna.  
  2. Choose the appropriate switch in the back for coax or balanced line antenna (Up for coax, Down for balanced line).
  3. Start with the inductance switch on the back set to low-impedance (Low-Z) because it is the most efficient.  It uses the 6 turn secondary rather than the 12.
  4. Switch the front switch to "Tune"
  5. Key the transmitter and be sure you are using 5 watts or less
  6. Turn the "Load" knob first until you see a dimming of the LED then the "Tune" knob to make it go out completely
  7. The knobs interact so you'll need to go back and forth between them to achieve best match
  8. If you can't get a good match switch the inductance switch on the back to "High Z" and try again
  9. Don't apply power too long at a time during tune because the 50 Ohm resistors are heating up in there during the Tune process
  10. When the LED goes out or gets very dim you have a very good match. Switch to "Operate" and enjoy a well matched antenna

Photos





Result of having to rewind the secondaries made it messier than I'd like
















Dimensions





Remarks

Qrpkits offers a great little kit that results in a commercial looking product. You end up with a small portable tuner plus SWR indicator that reduces the complexity of your portable operation.  Pacific Antenna is very responsive to questions. I sent a question concerning the incorrect instructions I'd downloaded for the antenna bridge and James answered me the same day with a different link (included above).

So if you have a QRP radio that needs an antenna tuner I recommend this kit. It's well thought out and works well.

That's all for now

So lower your power and raise your expectations

72/73
Richard, AA4OO

The Grand Illusion

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?

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.

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.

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. 

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.
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.  
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:

STEALTH_bigWell 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. ?


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