Home Antenna Considerations, Part 1.

 I am doing some considerations on a re-design of my antennas in and around the house. Right now I have a more or less functioning system, because during the pandemic I have not had the option of people coming to assist in antenna installations. 

The antenna system was due some maintenance the last 2 years, so now is probably the time to get started again.

This is my existing antenna system:

1) RX-ant:

- Active Mini-whip: 10kHz - 25MHz (needs some distribution/filter circuit(s))

- Indoor loop: 500kHz - 30MHz (lower than 500kHz w/amplification?)(needs distribution/filters)

- Loop on ground (30 - 160m, maybe MW/NDB bands w/ amplification?) (needs distribution/filters)

2) TRX-ant:

- R6000 (10 - 20m) (6m poor(RX only?)). In working order, but guy wires need to be replaced.

- Low 5B dipole (10-15-20-40-80m). Not very efficient due to the low height.

- V2000 (6/2m/70cm vertical). This is in working order.

- Corner vertical (mounted at the corner of the garden). This antenna has lost the top. I will have to check if the telescopic fiberglass mast has partly collapsed, or if it is broken. Originally this antenna worked in varying degrees on 160 - 30m, but it has certainly lost the 160m capability. Most definitely needs maintenance or re-design.

- Big Wheel, 2m (could possibly do 70cm) Omnidirectional, horizontal polarisation. This is generally in working order, but in rainy conditions it seems to deteriorate. Probably leaking, so needs maintenance.

- 10m 1/2 wave antenna. In working order.

- Low 2m/70cm vertical w/lossy cable. 

I am trying to make the antenna system as unobtrusive as possible, still with the functionality I want, so here are some requirements:

TRX Operation possible on following bands:

- preferably a possibility og making at least one QSO on 2200 and 630m. This may be tricky, but should be tested.

- 10 - 160m, reasonably well.

- 10m good (minimum as good as a vertical 1/2 wave).

- 4/6m needs to be improved (probably with Moxon, capable of running more power)

- 2m added gain, horizontal

- 70cm horizontal gain

- 23cm vertical and horizontal w/ some gain

- 13cm vertical and horizontal w/ some gain

- 9cm ???

- 6cm (maybe "14dB" patch array)

- 3cm 15/17dB horn or small (35cm?) dish

- probably some antennas should be capable of more than one band.

Diverse RX antennas: 

- Mini-Whip (2 pcs?). Will need distribution/filters

- Indoor WB loops for MW/HF. Will need distribution/filters

- Outdoor WB loop for MW/HF. Will need distribution/filters

- Outdoor loop for MF/LF(/VLF?). Will need distribution/filters

- Loop on ground antenna for MF/low HF bands. Will need distribution/filters

- other possible RX antennas may be considered, e.g. 4/6/10m RX antenna, 137/145/250MHz, 432MHz, 23/13/3cm monitor antennas.

I do have some ideas, but I think I will have to take yet another look at the garden and assess the possible solutions, so this is all for today.

Week End Activity, P.3: Loop on Ground Receive Antenna Experiment.

 The loop antenna adventure continues.

This time I revised the Loop on Ground (LoG) setup.

Some time ago I tried out a LoG made with field telephone cable. This cable is mostly made of steel wires, but with a few strands of tinned copper wire, in a 4x5m configuration. Probably not the best material for antennas, and the results were disappointing, and the experiment was halted. Now it continues.

After cutting the grass (first time this year, so it took some effort) I found some thin wire to lay down. It may be replaced with weatherproof wire later, but I got to test the system, this time the wire is a bit longer, the configuration is about 5x8m, so the highest band expected to work properly is 30m. I use pegs to hold down the wire, the type used to hold wires for robotic lawn mowers.

The box with the transformer had to be repaired, too, one of the transformer wires had disconnected since I last made the experiment.

I am testing with the IC-7600. Here are the first test results:

Initially the noise level all over the bands was poor, but winding part of the cable a round a ferrite rod near the radio improved that. A better common mode choke is desirable. Now I need even more ferrite (toroids and other stuff) for reducing RFI all over the house.

MW/LW sounds quite noisy and with low S/N reception. Not as good as the small NCPL (w/amplifier at the radio), and certainly not as good as the Mini-Whip.

160m sounds OK-ish with no preamp, not spectacular

80m sounds good, signals weaker than on the low hanging dipole, but noise lower, too. Almost equal, but I suspect that the 

60m sounds good, not spectacular, looks like it is a bit noisier than the dipole (using Shannon Volmet and FT8 as test signals), but then again, the dipole is not resonant on 60m.

40m weaker than the dipole, but sounds quite good. Comparable S/N.

30m looks quite sensitive, no resonant antenna to compare with yet, but it sounds like a decent receive antenna

20m: Looks like S/N is worse than the R6000. No surprise, as the Loop on Ground is too large for 20m

I suspect that the best band for this antenna will be 80m. 40/60/160 are probably OK with a better set of common mode chokes at antenna and radio.

On all the bands the noise floor of the receiver increased when the antenna was connected, so the IC-7600 receiver is sufficiently sensitive on all the bands I intend to use it for. It should also prove a decent receive antenna for use from 1.6 - 12MHz. I think I shall keep it and probably replace the wire, then get it closer to the ground, maybe a few cm under ground level. With some weatherproofing this should prove an interesting low band receive antenna in the winter season.

My Home Made NCPL (YouLoop Clone).

 I made a prototype version of the NCPL (Noise Cancelling Passive Loop) receiving antenna.

This version is the same size as the YouLoop, but made with RG-58 cable, cross soldered (shield to inner and inner to shield at the top, then pushed through a hula hoop plastic tubing.

The ends of the tubing are inserted into a distribution box for electric wiring at the bottom. The shields are soldered together there, and the inner conductors are fed to a transformer made with 2x4 windings on a type 73 binocular ferrite core, one end connected to the shields and to the ground part of a SMA connector, the other end to the center of the coax connector. A better mechanical construction is needed, but a preliminary outdoor test can be made when the weather permits.

Testing:

Under test the home made loop behaved, essentially, as the commercial loop with respect to frequency response and signal strength. Not unexpected, and encouraging for the next experiment with NCPLs, another loop almost 2.5x the size of the original.

Due to the small size of the loop, signal strength on the lower bands is quite low. Experiments with amplification are in order.I suspect that the S/N can be improved significantly on MW/LW for this antenna, because many receivers/transceivers have low sensitivity below 1.6MHz, and the atmospheric noise is quite high on the low frequencies. I found a simple 2 transistor design presented by N1KPR, with 15-20 dB gain and a reasonable dynamic range, and I think this should be the first test with low frequency amplification, and probably be mounted outdoors near the position of the antenna. After this I can think of making an indoor distribution system with some band splitting, more amplification (pet band) and possibly a pre-selector system for the receivers. 

For the larger NCPL the intention is to use the thin Teflon coax cable (RG-316(?)) for inserting in the tubing, because the fitting holding the tubing parts together will probably not have enough space to fit the cross connected pieces of RG-58 inside. The thin RG-174 could probably be used, but the Teflon cable is more heat resistant when soldering, and more mechanically stable. Experiments with a different transformation ratio and some amplification should be made to see if the VLF band (down to about 10kHz) can be covered with sufficient sensitivity.

Because the system will be more usable in the winter half of the year, there is no great haste needed, but the bigger loop should definitely be made and tested. After that, I should focus on 2, 4, 6 and 10m. The Sporadic E season is right around the corner.

The Small Loop RX Antenna Adventure Continues.

Slightly updated.

 This is another attempt to achieve a good receive antenna system for monitoring different frequencies in as many (ham) bands as possible.

Stage one was the experiment with the Mini-Whip described in recent posts.

The active Mini-Whip did provide some decent to good reception on frequencies ranging from 16kHz up to 18MHz.

Not bad for such a small antenna.

Now the experiments have started for a small passive wideband loop antenna. The main idea is not new (at least 60 years old), but there has been a resurgence of interest since SDRs with good sensitivity and with reception capability on VLF have started becoming available at reasonable prices.

Looking at the "YouLoop" antenna made for use with the Air-Spy SDR I decided to look into this. 

This is in essence a "Moebius Loop" type antenna, a design invented in the 1960s, as far as I know. A version is available at the well known auction site, so I took the lazy way and purchased one, just to see what all the fuss was about.

This is the initial result of a quick comparison of the Mini-Whip and the YouLoop:

First I want to point out that the YouLoop as purchased is not suitable for outdoor use - no waterproofing.

This means that the Mini-Whip is mounted outdoors in one of the least noisy places I could find in my garden, furthest from houses, mine or neighbours' houses, and the YouLoop was hung inside the house, in the noise field.

Because the Mini-Whip is active the signal level is much higher than from the small loop. However, whereas some signals were audible with the active Mini-Whip and too weak to be heard on the loop, others were swamped in noise on the Mini-Whip and weaker, but clear with the loop. 

I am aware that the loop might benefit from a sensitive preamplifier, especially on low frequencies and with low sensitivity receivers. This I need to test.

Signals on the loop were a bit weak and noisy on medium wave, and somewhat comparable in S/N to the Mini-Whip on 1.8 to 10MHz. Above this the loop did not increase the receiver's noise when connected, indicating either insufficient sensitivity of the receiver (possible) or simply a too low output of the loop. MW was full of rather strong signals with the Mini-Whip, and considerable weaker (and more noisy) signals came from the loop.

I suspect that a low noise preamplifier at the loop will improve this, especially if a long cable is used. Oh, darn! more projects ;)

Having seen the results I decided to make my own (weather proofed) version of the loop. I already had some hula-hoops (yes the children's toy ones) stored and found a few of them. The first test will be a loop of similar size to the original "YouLoop" (My YouLoop clone). Using two lengths of RG-58 soldered together crossing the shield and inner conductor at the top of the loop, feeding the inner conductors at the bottom to a 1:1 transformer (type 73 binocular ferrite core), and connecting the shields together at the bottom. Here is a description already made, so I will not repeat everything. I will report back when the test has been done

I will have to check whether or not a connection of the feed cable shield to the common shield is beneficial wrt noise performance. I suspect it will be.

I have two more (larger) hula-hoops, so I intend to test a larger (2.5x or so) version of the loop for getting higher signal strength.

The loop antennas do have another advantage over the Mini-Whip: They are directional and have a null, making it possible to reduce interference/noise by turning the loop. For now I intend to use both the Mini-Whip and loop antenna, and switch between them to get the best possible S/N on a given signal.

Using separate receive antennas is beginning to take shape, and with the addition of a distribution system,  preselector/filters/amplifiers a decent propagation monitoring system, such as FT8/WSPR and/or beacon/QRSS monitoring.

Ground connection for the Mini Whip. RX Test.

 I have a ground rod on the Mini Whip now. Not too far into the ground, about 60cm/2ft. Hammering a 2m (8.5ft) ground rod is tricky without the right tools ;)

The results are interesting:

A relatively detailed review was done today, by dialing slowly through the bands. Starting downwards from around 18MHz indicates that the sensitivity/SNR has improved reception on frequencies from about 1.8MHz up to 18.2MHz, maybe higher.

Medium wave is not bad, with signals on essentially every channel in the whole band, with a reasonable SNR, probably increased sensitivity.

NDB band appears noticable worse wrt SNR, possibly partly due to overload from MW stations in the evening, but noise level seems to have increased.

LW seems OK, not spectacular.

VLF (<100kHz) seems more sensitive, but with more noise. possibly due to overload of the RX. 

A different Mini-Whip with a real whip antenna (1 - 3m long) might improve sensitivity on VLF/NDB bands, but should probably have a low pass filter with a 3dB cut-off frequency of 530kHz. Because a thin whip mounted low is not too visible I might add this to my antenna farm, just to see how it works. If it works well I can make a permanent installation.

Because the Mini Whip is very broadband it may be an advantage to make some filters in any case, possibly as follows:

Low pass with 150kHz 3dB point, for the 136kHz amateur band and "VLF" reception.

Band pass with 150kHz high pass and 530kHz low pass, mainly for the NDB/marine bands and 472kHz amateur band.

MW band pass with 530kHz high pass and 1700kHz low pass.

MF band pass with 1700kHz high pass and 3MHz low pass, mainly for the 1.8MHz amateur band.

HF band with 3MHz high pass filter.

If I get all working nicely I may make a (set of) distribution networks, possibly with switches for the different receivers.

Yes, I like monitoring a lot of frequencies I do have some receivers, everything from purchased amateur equipment to portable transistor radio(s) with external antenna input(s), and, of course some SDRs, and some simple monitor receivers (e.g. a Pixie kit for 40m), and some that I may build. At some time I have been monitoring (audio or data) on 14 different frequencies simultaneously, part of it as monitoring propagation, and I expect this record to be beaten ;)

This is also part of my intention to make a contact on as many bands as possible with (at least partly) home made equipment.

Another Receiver on the Mini-Whip. VLF Reception.

 For a few days I was using my old FRG-100 with the Mini-Whip. The receiver appears to have a rather wide IF filter, meaning that I could hear a carrier all the way through zero-beat (part of the other sideband audible) Not good for listening to AM signals.

Also the lowest frequency I can receive with the FRG-100 is 130kHz. I would like to listen to lower frequencies.

Enter an old AOR AR-7030 I have. I think, according to the specification, the receiver covers 30kHz to 32MHz. Very nice, even if I wanted to test it on a lower frequency. Actually, the AOR frequency dial goes right down to 0kHz. Well not really. on the very lowest frequencies it is totally deaf (no surprise).

Tuning upwards with the Mini-Whip connected the noise starts coming up around 10 - 12kHz. Now it gets interesting. The lowest frequency signal I could receive (until now) is on 16kHz (origin unknown). This means that I should be able to receive the SAQ transmitter from Grimeton, Sweden, next time it has a transmission.

Further, the filters in the AR-7030 are clearly better than those in the FRG. Mounted in this RX are IF  filters with bandwidths from 2.1kHz up to 9.5kHz, in several steps, and also tone controls for bass/treble. There are even better filters in my transceivers, but those have a lower frequency limit of 30kHz or more.

Never the less, VLF signals from as far away as Grindavik, Iceland on 37.5kHz were heard in the day time. Strictly speaking not VLF, but definitely a nice reception. This is a data signal that I did not attempt to decode.

The station in Cutler, Maine (US) was not audible with this set-up, but then again, the antenna is not yet optimized for lowest local noise level. The weather and other activities have been in the way of connecting a ground connection to the antenna. and other steps.

Tuning up through the band, all the way up to 518kHz NAVTEX frequency I now come across a lot of signals. In particular I now hear more NDBs (non-directional beacons used for navigation) in the 300 - 500kHz range, along with other signals of unknown origin (to me at least)

One surprise was a signal on 505kHz:

OK0EMW in JN88ks running CW identification (with Locator) and some QRSS, too.

This must be a remnant of the activity that was allowed on experimental basis on the "old" 500kHz band. I was not aware that there was any activity there any more. Apparently the (QRSS) etc beacon was allowed there those years ago, and the permission has not been revoked.

There is much more to do regarding MF, LF and VLF reception. One thing is to test if I can really hear the SAQ transmission next time it will be active.

Another test should be using my IC-7600 for reception on LF/MF. With the much better (DSP IF) filters reception of many more NDBs and other signal should be possible. There is a lot of noise in that part of the band, so every improvement of the receive side will count. Also, a set-up with a low frequency SDR should be done. The first SDR experiment should be with the RTL-SDR in direct sampling mode, then maybe later I will get a more suitable SDR, also for those frequencies

For the lowest frequencies a test with a computer sound card should make reception up to 24kHz possible, maybe even up to 48kHz with 96kHz sampling.

Active Receive Antenna: The PA0RDT "Mini-Whip". First Experiments.

 A little while ago I purchased a Mini-Whip set (the outdoor unit and the bias-tee) from Chine. Quite inexpensive, and now when the weather is improving (some days, it is April, after all) I started an experimental set-up.

I was aware that I should avoid noise from entering the antenna via the outside of the coax, so the first step was using a common mode choke (CMC) at the antenna, with a low cost (green) EMI toroid from China.

The antenna is mounted on top of a 4m long telescopic fibreglass mast, intitially just attached using duct tape, placed at a relatively low noise point in the garden with more or less optimized distances to all surrounding houses. This is sufficient for the testing and can be changed later. The power supply is a battery, just to avoid noise entering directly the system via mains power.

The result was quite disappointing, but not entirely unexpected up to 7MHz there was a substantial noise floor, reducing the signal-to-noise ratio (SNR) when compared to a multiband dipole I have in the garden, and the noise level on medium and long wave (MW, LW) was killing all signals less than S9 Even then, and this was encouraging, more than half of the MW frequencies showed audible stations before sunset.

Next step: Adding a "SW" CMC just next to the bias-tee. This was using a FT 240-43 toroid core with 2x10 windings of RG-174 coax. Progress: The noise was reduced on SW, now the Shannon VolMet on 5505 was audible with a decent signal, not quite as good as with the dipole, but a definite improvement. MW was still quite noisy, and LW not good enough. Very few NDBs (Non-directional beacons, mostly situated at airports) were audible in the 300 - 500kHz band. signals on 472kHz were still drowning in noise.

Yet another step: A second LF CMC was added (one more of the green Chinese toroids) was added, making MW quite usable, though not perfect.Several NDBs popped out of the noise, and with better filters in a receiver there would probably be many more to find. The usable frequency range was extended to 400kHz up to at least the 30m amateur band at 10MHz. The Shannon VolMet now has a SNR comparable to the dipole. Good progress.

This is the state of affairs at the moment. There is still too much noise for my taste, but at least I can work on removing noise coming from my own house.

There is more to try:

1) adding a second (MF/SW) CMC at the antenna. This is not too difficult.

2) Adding a ground connection directly to the ground of the Mini-Whip PCB, "bypassing" the CMCs at the antenna.  This will take a bit longer because good weather is necessary if I want to solder outdoors. As an alternative the antenna could be dismounted and the soldering could be done indoors. Further, a 2m ground rod should be hammered down.

Still more to do with this receive antenna system, but it is a decent start