Posts Tagged ‘stealth antenna’
As I have shared in the past I have a 66′ dipole in the attic fed with ladder line. I live in a HOA controlled neighborhood so my antenna options are pretty limited.
Last night I set WSPR up running 2 watts on 20 meters. Started about 2200 UTC. Wow it really seemed open. My 2 watts was spotted multiple times into Europe, Alaska and all over the USA. This antenna does not have a problem getting out.
The problem with my antenna setup is on receive. I have minimum S5 noise on 40 and 30 meters. Typically S7 on 20 meters. Interestingly enough 15 is quieter and 10 meters is typically S2 or so. The noise is static with some noticeable “crackling”.
Last night on WSPR was a great example. I was getting heard ALL over, but I was only decoding about 2 or 3 stations – all in the USA. Also on PSK31 or JT-65 I see guys working DX that I can’t even here or see on the waterfall – my noise level is just too high.
Sometime soon I am going to cut all the power to my QTH and see what the noise level is. If significantly reduced, I will see what I identify as noise sources in my QTH.
Beyond that, less than a 1/4 mile as the crow flies I have identified some very noisy power lines. They are so noisy that it they will completely blank the AM radio in your car when you drive past them.
Here is a picture of where my house sits in relation to the power lines (my dipole runs parallel to the power lines):
|Blue marker is my QTH – Red line is power line (X’s are noisy poles)|
I will be contacting the utility company at some point, but first I want to see how much of the noise is coming from my own QTH.
|Red markers are trees – red line would be horizontal leg of inverted L|
|66′ Dipole ready for the attic!|
Over the 3 day weekend I finally squeezed in some time to get my 66 foot ladder fed dipole up in the attic. One leg of the antenna is basically straight, but the other leg had to do a bit of zig-zagging through the trusses – it gets a bit crazy up there!
The ladder line drops down into my garage and then down to the basement where my shack is located.
Last night I built the BL2 1:1 or 4:1 balun from Elecraft. The ladder line terminates at the balun and a 3′ piece of coax goes from the balun to my KX3.
Wrapped this all up last night about midnight – and then started doing some testing. The internal tuner on the KX3 tunes ALL bands 40-10 meters almost down to 1:1 SWR. Very nice.
I tuned around 40 meters and only heard a couple stations that time of night. The noise level last night was between S4 and S5 – not sure if this is the normal noise level or not, but I suspect it is.
I did a bit of testing using the RBN – I called CQ on 40 meters for a few minutes and ended up with spots North, South and East of Kansas – good sign. Then I switched antennas back to my 9:1 UNUN 30′ wire in the attic and did the same thing – so reports. So good news is that my performance on 40 meters is GREATLY improved. The reports on my 66′ Dipole were from 10-18 DB SNR on the RBN – all with 5 watts out of the KX3.
At 1:00 am local time I heard K0GPA calling CQ – he was 559 here. So I threw out my call and he came back to me with a 559 as well. Turns out he was running a KX3 also – he was at 10 watts, and I was at 5 watts. The QSB got him a bit, but I think he was using some type of loop – just missed what type. It was a nice QSO with Bob – and it proved I was getting out!
So now I am looking forward to putting it through the paces a bit more and see just how much my reception will improve with more wire in the air! I hope to at least have time to look at the waterfall tonight on 20 meters PSK31 to see what it looks like compared to my old antenna.
I will keep you posted!
So I got a little time over the weekend to make some progress on my magnetic loop antenna. I constructed this antenna from 1″ copper pipe in a square shape with 90 degree elbow. The loop is 30″ square.
At this time it will be rockbound on 20 meters, centered around 14.060 – so the bandwidth will be very limited. I want to do this so that I can do some testing before I go all out and convert it into a multi-band loop, which will hopefully work on 20-10 meters (with maybe 30 if I am lucky).
Making the Coax Stub Capacitor
So what I did was take a piece for RG-213 coax and cut it about 30″ long. Then on one end I removed about 2 1/2″ of the shield and pulled the braid away from the core. I taped it all up really well with multiple wraps of electrical tape, leaving about 1/2″ of braid and 1/2″ of conductor (sticking out of core).
After sanding the copper to a nice shine, I took some stainless steel hose clamps and clamped the braid to one side of the loop and the center conductor to the other side.
This piece of coax becomes the capacitor which will be used to tune the loop to the desired frequency. Right now it is longer than needed so it will resonate well below the 20 meter band.
The Feed Loop
I then took some RG-8 and made the feed loop. For my loop size the feed loop is about 1/5th the circumference of the main loop – so about 24″. I added a bit for the coax connector. I decided on a shielded Faraday loop after reading that they are quieter on the mag loop email list.
To construct this loop I formed the circle and soldered the center conductor to the braid at the bottom of the circle. Then at the top of the circle I removed about a 1/2″ of the braid only. I taped up all connections and exposed braid, etc.
I quickly taped the Faraday loop to the main loop with some painters tape because I wanted to see how it looked just sitting on the bench. Before I do the final tuning I will hang the loop on the wall of my garage – its final home. I was just excited to see where it was resonant!
So I hooked up the antenna analyzer and started a slow sweep from 20 meters down looking for the SWR dip. THERE IT WAS SWR 1.2 @ 11.131 MHZ – clear as day!
The next thing I am going to do is mount the loop to a piece of 1x wood and then mount that on the wall at its final location. Loops are sensitive to their surroundings, so you always want to tune them at the location they will be when completed.
Then with the analyzer connected I will start cutting 1″ chunks off the coax until I get close to 14 MHZ – the final tuning will be done by sliding the braid up and down the core to get the frequency exactly where I want it.
Once it is operational I will spend some time testing with the Reverse Beacon Network and making contacts. If it works well, ultimately I will construct a butterfly capacitor for tuning and build an Arduino stepper motor controller so that it can be remotely tuned from the shack.
I can’t wait to see how it works and if the noise floor is substantially lower than using my Portable QRP Vertical.
If you would like to construct something similar (although he shows a Gamma Match for the feeding) you should check out W2BRI‘s pages – great instructions with pictures to make everything easy.
|30″ Magnetic Loop Under Construction|
As the list of major projects at our new home is starting to get shorter, I have been pondering an antenna installation that is more permanent than my Portable QRP Antenna that I strap to the deck railing when I want to operate.
The portable vertical I use, which is nice and quiet at the park, is VERY noisy at the home QTH which is full of all sorts of man made electrical noise.
First thought was to put a 66′ doublet in the attic and feed it with ladder line. I have no doubt this would work, but I have to invest in ladder line to make it happen.
I have a 30″ square magnetic loop that I have built from 1″ copper pipe before we found out we were moving. It is all soldered up, just sitting in my garage waiting for a tuning capacitor and feed loop to be installed. I am leaning towards this being my first antenna install here at the QTH.
Why a magnetic loop?
You can read all about the good and bad of loops online, but one of the biggest drivers is that they are supposed to be very quiet. Many hams that report S5+ noise on their dipoles are reporting S1-S2 noise on the loop.
The other reason is that it is almost done – probably a couple hours of work max and I could have it on the air. Additionally I can hang this in my garage, or put it in the attic, so that I can keep in good graces with the ever watchful HOA observers!
So that is what I am going to do. At first the tuning capacitor will be done with a coax stub tuned to a fixed frequency. I will do this centered around 14.060. This will give me a narrow little spot to play.
Then I am going to build a home brew butterfly capacitor – which I will document here.