Screwed Up by Photobucket

Several years ago Photobucket changed their policy of linking to images stored on their site.  They demanded payment at some ridiculous level to continue linking to my photos on their site.  OK, it is their site and I know providing networks, servers, and storage for all those images takes money.  I stopped adding photos on Photobucket but maintained what I had on the site.  For the most part the links continued to work.  Not long ago I got an email stating they changed their policy again.  I had too many images stored on their site to qualify for a free subscription. 

Fortunately, I never used Photobucket (or any other site) for my primary storage of photos.  I maintain my own local storage and at least two backups of all images.  The online sites are mostly for convenience of being able to show others my photos and linking to pages such as this. 

I got fed up with Photobucket and deleted my account and all images on their site.  I had forgotten I used their site for images on this blog.  Other than more recent posts all my images here are now broken links.  I have all the original photos.  I just need to figure out what photo went to what post.  I will try to fix those over the next few months. 

Just goes to show don't trust any third party storage service.  Be it for photos, music, files or what ever.  This is especially true if using a "free" site.  I don't trust my paid sites either. They could change policy or just go out of business at any time.  Always maintain your photos somewhere where you have control. 

Common Mode Choke for VLF

Adding a common mode choke to the Ground Probe Antenna. I don't think it will help with the noise on 474 KHz as I don't think it is coming out of my house.  Won't hurt to add it. The purpose is to keep noise signals that propagate along the transmission line from getting to the antenna. I wound this using the same core I used for the matching transformer on the Ground Probe Antenna.  It was wound with insulated #18 wire I happened to have.  Around 23 turns, two conductors twisted together. 

I use a drill to twist the wires before winding the core.  Clamp one end of two wires into a vise.  Clamp the other end into the drill chuck and let her wind away. 

Differential mode loss is less than 1 DB.  Common Mode loss was taken with my MDO3000 scope using the function generator to generate flat broadband noise from a few Hertz to past 2 MHz.  This image stops at 2 MHz.

Common Mode Response

The spikes are local AM broadcast transmitters.  The input noise level to the choke was -59 DBm. A table of the data is listed below

Frequency KHz          Loss (DB)

25                                  -13
50                                  -20
100                                -27
250                                -33
350                                -37
450                                -39
500                                -40
700                                -42
1000                              -42
1200                              -41
1500                              -39
2000                              -37

 This will be installed in a junction box that is near the feed point of the antenna. It is about 5 feet away from the connection point. If there are any noise signals on the coax line this should reduce them. 

630 Meter Interference

I had a chance tonight to examine the interference that is blocking reception of the 630 meter band in the evening.  Last night the interference stopped abruptly around 11:15pm local time.  As I suspected the noise returned tonight.  I was out when it started but it was in full force when I returned at 7:30pm.  This gave me a chance to examine the noise in more detail.  First was to look at the audio coming from the receiver.  What this shows is a series of pulses space approximately 8.2 ms apart.  The inverse of this is the frequency which is around 120 hz.  That is why I hear the low frequency buzz in this interference.  I have observed a similar pattern with arching of high voltage distribution hardware.  In that case the noise was very broad band.  Covering from HF into UHF.  In this case the noise is limited to a much narrower bandwidth.  Considering the bandwidth and the way it shuts off I am sure this is a device and not power line hardware related. 

 

Looking at the FFT signature of this same audio sample I see a square pulse that starts around 115 hz and ends around  3.488 KHz.  I think that is why, on Spectrum Lab, I see flat audio response out of the receiver for its full 3100 Hz bandwidth.  The FFT image is shown below:

Looking at a spectrum analyzer from 410 KHz to 500 KHz I see the following.  This essentially wipes out the 630 meter band. 

It will be interesting to find out what this is.  I suspect this is a television or something in the room with a television that household turns on in the evening and turns it off when they go to bed.  So far I have not heard this noise during the day (Monday - Friday). 

To track this down I plan on taking a ferrite rod and build a loop stick antenna. Those have a sharp null off of the end of the rod.  Walking around the neighborhood I hope to be able to use that null to at least locate the house where it is coming from.   Of course I need to make sure it is not something within my own home.  That would be an easy fix if that was the case.  Since this shut down last night around 11:15pm I can not think of anything in the house that would have done that last night. 

Ground Probe Antenna

Ground probe antenna which some call them Earth Probe Antenna.  It consists of a long wire terminated with ground rods at each end.  Looks similar to a Beverage antenna which is a very long wire terminated at the end.  The wire being only a few feet off of the ground.  These are low noise antennas directional off the end.  Best used for DX on 160 meters as their directivity and pickup of local noise is much less than an Inverted-L for example. 

The Ground probe antenna is used for reception of ELF and VLF signals. This post will describe the one I put out on my property in the suburbs.  My back yard is around 175 feet wide and I was able to run a wire out 158 feet (41 meters).  For now the wire is just laying on the ground.  I drove 8 foot ground rods at each end.  I connect to the antenna approximately in the middle.  I am not sure how to feed this antenna so I did so in the middle as that was a convenient location.  Some on suggested the impedance magnitude was around 1000 ohms.  With further measurements I think it is more like 500 ohms. 

I have in my junk box a ferrite core of unknown properties.  I measured the AL value at 6490 mH / 1000 turns.  The material appears to be "P" or "F" ferrite used in switching power supplies running under 1.5 MHz. I am feeding the antenna with RG-6 cable.  I used 50 turns on the antenna and 14 turns connected to the RG-6.  I am going to change that when I get a chance assuming a 500 ohm Zmag rather than 1000 ohms.

I drove the ground rods below grade with a 12" long section of 4" PVC at the top with a cap.  The cap is flush with the ground so I can run the mower over the top.  I can still get to the ground rod connection by removing the cap.  I did the same for the coax connection in the center.  The transformer sits inside of the 4" PVC. 

 

First tests

It was 20:00 EST on February 3^rd when I connected the HP3586C up to the antenna.   Wide band noise was -8 DBm with the broadcast stations.  Cutting out the big three (WHIO, WING, WONE) with my trap filter the broadband noise was -21 DBm.  Noise with 3100 hz bandwidth on 630 meters sits about -86 DBm, except…… well I will get into that shortly.

Daytime levels for WHIO are -13 DBm and -10DBm for WING.  They are +10 DBm on the 160m inverted-L.

First to test was the broadcast band.  The antenna did very well from 550 to 1500 KHz.  Picking up many stations at night.  Better reception on the typical ones such as KDKA, WBZ,  WHAS, etc.  I did not attempt to dig down for the weaker stations.  I tried FT8 on 160 meters and that was a failure.  Only decoded three stations.  

Next test was WSPR on 630 meters.  A while back I ran this test on the K9AY loop before I added the 160 meter high pass filter to cut out everything below 1.7 MHz.  That did very well.  So how would this antenna compare?  Well…. I ran into a brick wall.  Or I should say, a noise wall.  Before I said the background level was -86 DBm on the 86C.  That was after midnight.  At 8pm the level was more like -66 DBm.  It started around 400 KHz and ended below 550 KHz.  I tried to determine a signature of the noise but could not find any frequency peaks or repeating pattern. It has a low frequency buzz similar to 120 Hz.  I could not hear anything through that junk.  To my surprise it abruptly ended around 23:15.  Someone shut something off.  It is not present during the day.  I am leaving the receiver on to try to determine the hours of operation of the QRM.  When it is off I hear 630 meter WSPR very well.  Image of map attached.  On this map notice a K9 stations in Hawaii.  At first I thought that was bogus but looking at QRZ he does live there.  There was another “W4” stations in the southern pacific.  If that guy is really there he has probably drown by now.  His QTH is listed in Tennessee.  As far as I know Tennessee has not annexed that part of the Pacific.  I assume he has his grid square setting messed up.  There are three stations on this map that did not appear on K9AY test.  A station in western Canada, the K9 in Hawaii, and a station in California. 

Next test was reception of Non-Directional Beacons (NDB) for aircraft.  List of the stations attached.  A couple of stations to note.  DDP is a 1KW beacon in San Juan, PR.  I am not surprised at that one.  The one I question is BBD in Brady, Texas.  According to the database that is MH class station. Those have a maximum power of 50 watts.  The database shows it as 25 watts which is typical of the class “compass locator”.  It was very weak but it was there and the frequency agrees with the database.  As you can see from my list all the other 25 watt “compass locators” were more local.  Last night I picked up three new ones.  One being QT which is a 1KW beacon on 332 KHz out of Thunder Bay, Ontario.  So far I have logged 29 NDBs.  I also received numerous of the Differential GPS (DGPS) stations.  I found a list of them all but did not make any attempt to log or identify those.

Of course the strong NAA out of Cutler, Mane, on 24 KHz was present.  I also could detect two other near 24 KHz. 

I have not heard anything on the Amateur 137 KHz allocation. 

Last night I could hear lightning static crashes.  Looking on a live lightning map the nearest thunderstorms were in the Atlantic near Bermuda.  The map indicated it was running a 4 second delay.  When I heard strong crashes four seconds later I could see a dot light up on the map.   So I got lightning DX into the middle of the Atlantic.  

As for that noise in the 630 meter band I plan on winding a ferrite loop stick antenna and see if I can track it down.  I fear it is neighbor's TV set.  At least they shut it off when they go to bed.   Maybe I will have more information in the future to post in this blog.  

Ground Rod below grade in 12" PVC pipe so I can get to the connections

Cap covers rod and transformer connections

Transformer for feed point to RG-6 coax

630 Meter WSPR station I heard the night of February 4, 2019

Antenna Voltages Near Broadcast Stations - 160 Meters

Wow!  It has been a long time since I posted to the blog.  I am still experimenting with various topics in Amateur Radio.  Just have not taken the time to document them here. I am now retired so will have more time to play with electronics and radio.

Recently I have been improving my 160 meter antenna system. I made a few changes to the Inverted-L antenna by spacing it farther off of the tower and getting the end wire out of the tree.  I still need to get the end wire higher up in the tree.  The wire is around 134 feet long.  80 feet go up the tower and the remainder horizontally toward a tree to the south.  The end of that wire is only about 25 feet above the ground. It should be more horizontal.  That tree is much taller but I can't get up in it any higher without a bucket truck or a man-lift.

I also added eleven radials fanned out over the back yard.  The radials are 67 feet long.  There is a reason for that which I should document in a future post.

The 160 meter band is just above the AM broadcast band.  I live with in 2 miles of the big three Dayton, Ohio AM radio stations:  WING, WHIO, and WONE.  These are 5000 watt stations running omni directional antenna during the day and directional at night.  The inverted-L picks up a log of RF during the day when the stations are running an omni pattern.  At night the directional pattern appears to be away from me as the signal level drops for all three stations.

For example, looking at WHIO (1290 KHz) using a frequency selective volt meter I see +16 DBm during the day on the inverted-L. At night it drops below 0 DBm.

Today I hooked up four 1N4148 signal diodes in a full wave bridge configuration.  I hooked that to the inverted-L antenna.  I get 38 volts open circuit from the diode bridge.  Short circuit current is 8 ma.  I placed an LED across the diode bridge output.  It lights the LED right up!

 

During the day I also have intermod problems from the high power stations combining together.  One 3rd order mix fall right on the 160 meter FT8 frequency.  Of course, 160 meters is dead during the day and the intermod mix disappears once the stations go to their directional pattern at night. This has not been a problem but it would be nice to eliminate the issue.  

At first I tried putting high-pass filters on the receiver. Thinking the intermod was from overloaded receiver front end.  That did not work so that tells me the intermod mix is coming from something external.   That could be anything.  Mixing in one of the transmitters, mixing from a rust bolt somewhere.   I am going to try to find it.  I am thinking a ferrite rod antenna built to resonate on 1.840 KHz might work.  Those rod antennas have a sharp null off of the end.  If it on my property maybe I can find it.   Snowball's chance in hell, but I will give it a try.