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.

Looking At My Antennas With The HP8753B

Using the HP 8753B Vector Network Analyzer I took a look at what my Classic 33 Yagi and 3-band fan dipole looks like from the shack. The Classic 33 is my original that dad got used back in the 70's It was refurbished once and installed at this QTH in 1989. The antenna has not been touched since. The feedline is Belden 9913 which was installed in 1989. Getting concerned that this air core coax may have water in it after all these years. For today's test the outside conditions are dry and have been for a couple of days. The Fan Dipole I put up last year. It consits of three dipoles feed from a common point. The dipoles are for 40, 30, and 17 meters. Dipole spacing and length of the elements are from a military document (Army I think) I found online. This document was written back in the 50's or 60's if I recall. It is installed as a sloper off of the tower favoring the west. I used the old 9913 coax that feed the 40-meter inverted V that this antenna replaced.

Looking at the Classic 33 first

I don't have a way to download the screen shot of the VNA so I used my Canon 30D camera to take a picture of the screen. I see I need to work on the focus. I used a tripod in front of the VNA but it was easily moved out of postion. If I am going to continue to use the camera I need to build a fixture that attaches to cart that holds the VNA.

The first screen shot is a Smith Chart view on 20 meters.

I was playing with the buttons on the VNA so now on to the Return Loss and SWR plots.

The SWR on the Classic 33 is not very broad on 20 meters. The yagi elements were installed favoring the voice part of the band. So the low end of the CW band suffers. SWR is 3.2:1 at 14.0 MHz, 1.16:1 at 14.2 MHz, and 1.6:1 at 14.3 MHz

15 Meters is better with the SWR ranging from 1.75:1 at 21.0 MHz to 2.0:1 at 21.450. Best SWR at 1.43:1 is at 21.160 MHz

10 meters is a wide band. The Classic 33 was intended to be used in the lower part of the band below 29 MHz. Installed for the SSB part of the band SWR ranges from 1.87:1 at 28.0, 1.17:1 at 28.3 MHz, 1.57:1 at 28.5 MHz, and 2.28:1 at 29.0 MHz. This image shows the return loss as well as the SWR in ().

The results of the tests look as I remember them when the antenna was installed at this QTH. After I made these tests I disconnected the yagi and placed a short on the end of the feedline. Using a return loss measurement and calculating the length of the coax line I came up with the following:

Length of line = 156 Feet

Loss measured at 50 MHz = 2.4 DB

9913 has a loss at 50 MHz of 0.9 DB/100 Foot according to one datasheet I found online. At 156 feet the loss per this specification is 2.8 DB. So this loss is within spec give or take my measurement error.

My notes from the installation back in 1989 indicates the disance from my connector panel in the shack to the connector at top of the tower is 136 feet. All the measurements I have made using the VNA or an MFJ analyzer show the length of my line to be 156 feet. Not sure why I have a discrepancy of 20 feet. I plan on changing out this feedline so I will measure what I pull out and see if my VNA or my notes are correct.

Now the Fan Dipole

Looking at the Fan Dipole return loss from 5 to 55 MHz you can see the three bands. Also a good return loss is noted around the 6 meter band at 49.5 MHz just a little shy of our allocation.

Looking at 40 meters the SWR ranges from 1.34:1 at 7.0 MHz to 1.8:1 at the top of the band, 7.3 MHz.

Moving to the 30 meter band. SWR is highest at the lower end of the band. 1.46:1 at 10.1 dropping to 1.20:1 at 10.180

On 17 meters the lowest SWR of 1.03:1 is below the band at 17.740 MHz. For the lower band edge of 18.068 the SWR is 1.7:1 rising to 1.8:1 at the top of the band. If I get ambitious I may try to shorten the 17 meter dipole a bit to pull the lower SWR inside of the band.

GE Mastr II Repeater

I have not done much in the ham shack for a while. Have many project to do but it seems like the time is spent in other areas. That is life I guess. Well I have a new projet that I have to get finished.

I am converting a GE Mastr II base station from commercial service to amateur radio repeater service. The original system was used as a base station up around 155 MHz. The GE is specified from 138 to 174 MHz but there were some component changes in models that operated below 150 MHz. Looking at web sites on converting these systems only the receiver has a few capacitors that need changed for optimum performance. The first step is to confirm the unit is working as it came out of service. Cleaning up the system I found there had been a mouse nest in the power supply. Had to clean that out. Apparently no damage caused by the unwelcome guests. Now on to testing the system. Testing the transmitter I found the output power was only 1.5 watts. That is a little off from the specified 100 watt output. There is a known issue where a strap that was placed between two PC boards to couple the output power from the finals to a filter develops a hairline fracture. The symptoms pointed to that as a possible problem. Turns out that was not the case. Since this was used in non-repeater service there is an antenna change over relay on the output. The relay had gone bad. Since I am using this for repeater service I don't need the relay so I pulled it off of the board and jumpered across it with a small length of RG-316 coax. Problem solved. I can develop the full 100 watt output now. For testing purposes I set the power output to 50 watts while I am doing the conversion. Next step will be check the receiver.

Catalog Filters

I was working on a project for the radio club and needed a couple of filters. One for 571 Mhz and the other for 735 Mhz. Previously I made a stripline filter and I have done copper pipe filters. These are rather large and I wanted something quick. Looking in the Digikey catalog I found filters by Toko. If you are buying a million of these filters I am sure Toko would make them exactly to your spec. For ham use in single quantity we have to take what is stocked in the catalog. Of course the catalog selection was made without consulting us hams to what we might need. The chance of finding something in stock value that is useful approches Epsilon. Much to my surprise I found a helical filter for 734 MHz with a 10 MHz bandwidth. Ok, lucked out on that one. For 571 the closest I could get was 550 MHz. Could I tune it up to 571? This little two section filter has tuning screws at the top of the cans. The screws were near the top so it looked like I was already at the top of the frequncy limit. As it turned out I was able to tune up to 571 MHz. For a test I ran the screws down to see how low I could get and still have the same overall filter response. The stock specification was Fo = 550 MHz, 10 MHz bandwidth. I don't recall the published insertion loss but I was looking at about 5DB. That was measured at the dip of the ripple which was approximatly 2 DB. My test jig was not ideal for grounding the cans, terminating the filter, and making connection to the RG188 teflon cable so I am sure I introduced some error in the response. The results:

Minimum Fo = 494.1 MHz
Maximum Fo = 586.0 Mhz

Other specs remained about the same but the insertion loss and bandwidth was increasing as I approched the upper limit.

For this filter I can pull about 8% from center but the catalog frequency was already near the top of the range. This would be unknown to the purchaser until after they examined the product.

If you need a filter check the catalog offerings from Digikey and Mouser. You may luck out and find something that might tune to the desired frequency but I would not try to go beyond 8 to 10 percent.

For reference this part was Toko type 7HW, Part number # 252HXPK-2736F (Digikey #TK3307-ND)