Thursday, October 17, 2019

WSPR - Turning off MW Band Attenuation for 630m

About three weeks ago I decided to turn off the MW band attenuation in the Icom IC-7300 - this is a sub menu option in the settings that is on by default. Wow what a difference! I started spotting stations much further away from Australia, Hawaii, Alaska, midwest to the east coast.

I've been spotting these stations semi-individually on and off, finally got a good selection of them in one night:
  • VK4YB - Roger's 630m antenna is something else.
  • K9FD - on a former AM broadcast site with radials intact on an Island, dream location!
  • K3MF
  • K5DNL - holds the distance record for a QSO on 630m with VK4YB!
  • KL7L


The antenna I'm using on receive is the ZS6BKW with no additional matching, just an HF 1:1 current choke at the bottom of the ladder line, remote ATU (bypassed) then 10ft coax drop to ground where it runs around to the other side of the house. The other RX settings I configure when running WSPR with the IC-7300 are NB and NR off, notch filter off, AGC fast set to 0.3 seconds.

Since turning off the MW band attenuation, I would start spotting the closer stations in California as soon as it got dark through until sunrise like clockwork. First I thought it was propagation changing with the D layer absorption which quickly disappears at sunset and quickly returns at sunrise.

Turns out it's more than the D layer at work, there are several strong AM broadcast stations in my area, during the daytime they are very strong and overload the receiver in the IC-7300. At night these stations lower output power and/or change their antenna pattern, this reduces signal levels at my location to a level where the receiver can cope.


Screen capture of the strong signal on 850 kHz during daytime, S meter maxed out at +60dB. There are several more at +40 to +50dB.


630m band WSPR frequency during daytime, the S meter hovers around S9 +15dB. Band scope shows the "mess" these strong AM broadcast stations create in the receiver.


630m band WSPR frequency at night, the S meter hovers around S1 when AM broadcast stations reduce power and/or switch their antenna patterns.

Note: The time displayed on the IC-7300 clock top right is UTC.

Sunday, September 22, 2019

43ft Vertical 80m/40m Matching & K9AY Loop

Note: This post is being updated/edited as the project progresses. Once complete, and if successful I plan to re-write it.

For this coming winter my 80m DX antenna system will be base matching the 43 ft vertical for transmit and using the K9AY loop for receive.

Reviewing 160 and 80 Meter Matching Network for your 43-foot Vertical by Phil Salas - AD5X. Phil provided a parts list in his article which I found to be very useful.

I decided to keep it simple and just have matching for 80m. I ordered the coil stock, 4:1 unun (not sure I even need that for my setup), ceramic feedthru from MFJ.

Did a quick throw together of the components to verify that things will work as expected:

 

Rainy day hence the umbrella, screwed the coil to some wood, current choke is 7 turns of RG-8X through two mix 31 clamp-on ferrites. Not having micro alligator clips made this a bit fiddley, but I got fairly close resonance and SWR wise.

My cunning plan is to use the vertical as a support for the K9AY loop, mount the K9AY relay box inside the 8x8x4” electrical junction box containing the matching network for the vertical.

With a simple control unit in the shack, when the rig is un-keyed, power will be supplied to the relay in the junction box which will open circuit the vertical (making it non resonant), unground and connect the loop feed-points to the K9AY relay box. Figure this is safer way to do it, if the system loses power I minimize the risk of sending TX power into the K9AY relay box which will let the magic smoke out!

At the shack end I will have one coax for transmit and one for receive. Since I have an Icom IC-7300 which does not have separate receive antenna jack, I got an INRAD RX7300 receive adapter for the Icom IC-7300. This allows you to use a separate receive antenna or insert things like filters into the receive chain for example. If I loop it via an antenna switch, I can choose when to use the loop on receive.

Update 29 Sept: I got the matching network in basic form built and tuned:



K9AY relay box top right - not yet wired up with the isolating relays.

Can see the coax tap point on the front side of the inductor, the antenna end enters through the top and is tapped on the rear. In practice I got a strange SWR curve with two dips, one around 3.6 MHz, and another at 3.8 MHz. Seems I accidentally made it broad-banded somehow.

Once I got in the shack to see how things looked with a radio connected to the vertical with matching network, the noise floor on 80m was quite high, nearly S9, will need to get the receive loop up and running.

When I reconnected the ZS6BKW antenna (near by), the noise floor on 80m was lifted near three S-units - safe to say there is some interaction occurring. After disconnecting the matching network from the vertical the noise floor returned to its usual daytime level of S2.

For now I disconnected the matching network, when the relays arrive I should be-able to get this completed, and remotely switch out the matching network to eliminate the interaction between antennas.

Update 05 Oct: Relays and some mini test clips arrived. I decided I should model the vertical with the K9AY loop in its presense, it has a small effect on the vertical's resonance requiring 12 uH vs 9 uH in the model to match it, but no difference in pattern or gain.


View in MMANA-GAL with a 55ft loop (35% smaller than the standard K9AY), the smaller loop maintains performance on 80m through 40m. Larger loops with better performance on 160m lose directivity on 40m.

Update 20 Oct: Some progress on the matching network. Relays mounted partly wired. Re-did the antenna connectors with a copper plated steel strip (found in the plumbing section at Lowe's) for better grounding. Top left is a SPDT relay, the blue "thing" is two 5 Meg ohm metal film resistors in parallel to bleed static via the inductor which is grounded at the bottom.

Control cable for the K9AY box top right is an RJ-45 socket mounted bottom right, I decided to standardize my control cable using shielded CAT5 cable. Hopefully the AWG size isn't too light, a test with 150ft of very cheap CAT5 seemed to work ok. Under the RJ-45 socket is a DPDT relay to isolate the loop from the control box when transmitting.





Making the square hole for the RJ-45 and marking the location of the holes for the mounting screws. Actually got it all spot on, which is quite rare for me!

Whats left? Quite a bit..
  • Finish the relay power wiring.
  • Make a mounting bracket for the loop top support.
  • Find the tap points on the inductor with everything in place and put appropriate gauge wire in place.
  • At the shack end I need to build a keying interface for the T/R switching.

Update 27 Oct:

For the last couple weeks I keep thinking about adding 40m to this system, and modeling it all together to see if it'll work. If this works out it might make a nice compact low band DX antenna system covering 40m and 80m with reasonable performance that'll fit in a modest back yard..

Over the weekend I worked out how to control the relays such that if I'm receiving on 80m with the loop, the vertical's matching network is set for 40m making it non resonant to the loop. Inverting that when going to transmit, and reversing the logic of the system when receiving on 40m with the loop, and via a simple control in the shack e.g. a two position switch. And "failing safe" in such a way that if power is lost, the loop isolation relay defaults to isolating the loop and vertical's matching defaults to 80m.. If that makes any sense..

Anyhow, it can be done with a relay, switch, and a solid-state relay driven by the Icom 7300 PTT accessory line (already using one in the keying circuit for the AL-80B amp).


Circuit diagram I threw together using an online tool. RY1 and RY2 are shown energized as they would be per the control unit when in receive mode on 80m.

Reviewing the idea of using CAT5 for the control cable where the loop control needs 6 wires (3 pairs), leaving a spare pair to individually control the loop isolation relay and vertical matching network relay, 24AWG can carry around 1 amp based on what I can find. The closing current of the relays is 100mA each, the calculated voltage drop over 75ft run is a couple of volts, if I use a 15V supply in the shack for this we should be good there.

Lastly, modeling the whole system as one to see if resonating the vertical via its matching network on the band not in use while receiving (e.g. if receiving on 80m with the loop, select 40m matching on the vertical and vise versa) is sufficient to have no interaction with the loop's performance. Short answer yes, appears this will work! Model file: MMANA-GAL 43ft TX Vertical with K9AY RX Loop.

Update 12 Nov:

I've had the loop operational for a few weeks, so far things don't look very promising at my location:
  • 160m: With a 55ft loop vs an 85ft (common size), I've found several occasions where the loop is noticeably better vs a horizontal wire dipole in terms of SNR meaning they sound louder on the loop, often it makes the difference of hearing vs not. The horizontal wire is a ZS6BKW antenna at 45ft, which is horrendously short for 160m at 93ft so it's perhaps not a fair test.
  • 80m: Not found a case where the loop was better than the horizontal wire antenna, when I've found a station on the west coast working DX, the loop makes no difference, either way I still don't hear the DX. Several times in the evenings I have gone searching 80 and 75m for situations where the loop shows an advantage or even pulls out further away stations that cant be heard on a horizontal wire, no joy there either.
  • 40m: Horizontal wire always better. Listening a couple stations in California working VK early one morning, out of several I could only hear one VK6 who was not quite readable on the horizontal wire, was worse on the loop. I think it's safe to say on 40m the K9AY loop is of no advantage. Frustratingly the stations in Cali were giving the VK stations 5/5 to 5/9 reports.

At this point I'm pretty much ready to shelve the project, too much local noise, not enough space for good antenna arrays, and pockets not deep enough for 60+ ft towers and antenna systems to match. Another couple points I've realized are:
  • My preferred time to actively operate is in the mid afternoon on weekends, this is at odds when the low bands are open. I had a bunch of fun last weekend in the afternoon on 40m chatting with a station in Utah for bit.
  • The second is after listening to stations actively working low band DX from the west coast is the QSOs are short, often just an exchange of callsigns and signal report. This doesn't excite me so much. I get a much bigger kick out of using WSPR to test the limits of propagation across a far wider range of bands as I can set it going and review the results when I have time.
At this point I think I'm going to follow the general crowd and do what works with more modest resources, 20m and above for DX, 40m and below for regional / NVIS. Time to start researching and planning antennas to suit.

Saturday, September 21, 2019

Gain vs Wave Angle

Something I've noticed is that most don't consider is the whole picture when it comes to antenna gain. Often only peak gain at the wave angle it occurs at is quoted. Sometimes a pattern is shown with no gain figures which is useless, this is often the case with verticals.

To build a picture of what one might expect when considering low band DX antennas, I feel it's better to consider the gain at different wave angles.

To illustrate this, I created a table in a spreadsheet with several different antennas and the gain they have at different angles. LiberOffice Calc has the option to fill cell background color based on the value. The table is sorted based on the gain at 5 degrees.



I used MMANA-GAL for the modeling of these antennas. Most are 40m antennas, those that can be matched on 80m are also shown.

Wire antenna heights are 40ft/12m, the inverted Vs are 15m/50ft, the delta loops have a minimum height of 1m/3ft.

From this table I can see that one of the simplest antennas gives the best bang for buck for DX on 40, thats the half square. A small surprise is the ZS6BKW on 40m looks to have an edge over a 43ft vertical for DX! The OCFD antennas are well behind.

Disclaimer: I'm no expert at modeling antennas, I perhaps know enough to be dangerous :-)

Monday, September 9, 2019

ZS6BKW Antenna

One of the antenna projects I wanted to get finished off this summer was get the 40m OCFD up in a flat-top configuration.

Got thinking about how I'd lack an antenna that covers 75m NVIS, thought about an 80m OCFD again. At 135ft long, the current situation with tree shapes, sizes and locations leave that easier said than done, and not for a lack of trying with out resorting to chainsaws. Having said that, getting one of two 80ft Fir trees closest to the house removed is on the list, so I may be-able put up longer wire antennas in the future.

What else is there that's under 100ft, at a minimum covers 40 and 20m with out the need for an ATU, and will work on 75m?

After considering a few ideas, I took a closer look at the ZS6BKW antenna which is an optimized variant of the well known G5RV. This antenna checks the boxes on these good points:
  • Light weight - no traps, coax etc hanging.
  • Low SWR on 40 and 20m, can run ~1kW with the AL-80B.
  • Respectable gain on 20m if you have the luck or luxury of orientating the broadside to favor somewhere of interest.
  • Will work on 75m with the remote ATU I already have.
  • Also covers 17, 12, part 10 and 6m with low SWR. 17m opens occasionally during the current solar minimum, and there is the Puget Sound 10m net on Sunday nights I like to take part in.

Spent a couple weeks reading everything I could find, and playing with models - one is included with MMANA-GAL, others can be found online.

Decided it was worth trying out. Initially I was going to order the parts from The Wireman and build it my self, but found a source of these pre-made cheaper and better built for $60 (normally $90) plus shipping from Amateur Radio Supplies => ZS6BKW G5RV 80, so went that route. 

Current setup:
  • Antenna apex at 50ft, ends in inverted V configuration.
  • K9YC inspired choke balun - 7 turns of RG-8X through two mix 31 clamp on ferrites.
  • Remote ATU between the choke and coax to the shack. 

How does it work?
  • Except for 15m, low SWR on six bands from 40 to 12m, parts of 10 and 6m.
  • Remote ATU dials it in on 75, 60, and 15m, brings the total to nine bands.
  • 30m is the odd one out, ATU fails to find a match in my case.

Nine bands where only three need an ATU, with 93 feet of wire in the air is OK by me. 30m might be an issue for some, but you can't always win 'em all :-) 

Links to further information:

What's next?
  1. Get the ends up higher - the test inverted V setup I have has the ends coming down too steep and into the trees, as expected resonance / low SWR favors the low ends of the bands.
  2. Maybe after the trees are "trimmed" it's possible I could move the antenna to where the vertical is with the existing radial field. This would allow me to operate it as a T (top loaded vertical) by bridging the two legs of the ladder line together at the base, and feeding it against ground resulting in an ok 80m DX transmit antenna in place of the vertical, eliminating one antenna from my setup.

What about low band DX? Not much progress there, and with winter approaching need to sort something out. Putting up the K9AY receive loop and building an 80/40m matching system for the 43ft vertical, possibly returning it to an inverted L is the "quick fix" solution.

Monday, August 12, 2019

Bay of Islands ARC Repeater Site

Following on from the Auckland VHF Group Repeater Site post, some more pics from the archives. This time of the Bay of Islands ARC Repeater Site, photos I took from around 2007 when I had the task of reinstalling the equipment after it had been removed for re-alignment.

This site was established with the help of the Auckland VHF Group in the mid 90s to get the national link extended north via a sister site between here and Auckland called Brynderwyn. NZART map here - its approximate at best. Google Map that I created here, the locations are with-in tens of feet in most cases.

Since these photos were taken when I was last there, the 2m repeater has had some changes with the addition of CTCSS for IRLP node 6398 link, there are more recent pics on their homepage and some from when the tower was erected.


Pic of the tower and antennas. Like Klondyke, the 2m repeater antenna is constructed from angle iron, welded, and hot dip galvanized, but is a simple pair of 2 half waves in phase for around 10 dBi of gain, hard to see as they are end on in this pic. At the top is a 4 dipole stack for the the 70cm repeater. This configuration resulted in the 2m and 70cm repeater performance and coverage being closely matched in most cases. The link to Brynderwyn is a set of four 7 element Yagis with around 17 dBi? of gain, the Brynderwyn end has the same antenna configuration, this is needed because the 70 mile path is not ideal.


Inside the building.
Tait T300 gear.
146.750- also had a 50W PA in the back.
439.975- had the matching Tait 50W PA.

Thursday, July 4, 2019

New Desk

After using a folding table for the last few months, 'twas time for a something better.

I had considered The Great Ham Radio Desk Project, but after looking around IKEA I found something I liked better, more so since IKEA was having a sale at the time.

The spare room/office/shack is 120" wide across the back wall. What I ended up getting were three sets of draws and two table tops, the table tops are 59" x 29", the 29" width is nice, as it allows plenty of depth for radios, computers etc with space in-font.


The total was about $270 less tax and delivery fee, took an afternoon to put together.



Left to right, Ameritron AL-80B, Kenwood TH-D72A HT on top, Motorola MCS 2000 33cm/900MHz radio, Kenwood TM-731A, Icom IC-7300, 27" iMac (2014, 5K), under the iMac is a Windows 7 laptop which runs all the ham radio applications.

Plenty of room for more stuff! Plan to add some shelves to mount the Kenwood and Motorola mobile rigs, control boxes, and antenna switches etc.

Saturday, June 22, 2019

Summer 2019 Antenna Projects

40m OCFD: I built the classical 40m version with 33% offset noted previously. For a quick "throw it up and see" test I had it in an inverted V config, the SWR and resonance results are inline with expectations.

I fired up the Ameritron AL-80B a couple weekends ago with the OCFD. On 20m propagation was the worst I've come across, managed one contact into Missouri but had to use the Utah WebSDR to receive as signals were weak. On 40m I later made two contacts into Utah, conditions were tough with static crashes from thunderstorms.

Listening to my self via the WebSDR, the 10dB gain of the amp makes a big difference. Sounded clean and punchy with the Icom IC-7300 driving at 70W with the ALC connected. The T/R switching is via a solid state relay interface I built as suggested by KV5R.

Inverted L / 43 ft vertical: Restored to 43ft vertical for now, OCFD needed the only high support I have via a tree that the horizontal wire ran to. Interesting note with the vertical, when it was last simply a vertical I had the radials laying on the ground, the SWR/match was a bit "gimmicky" in on some bands where for example on 20m, the remote ATU failed to find a match. With them buried 2" to 6" deep things are much more normalized.

What's Next?

Get 40m OCFD up in flat top config, and dialed in. At near 50ft it will cover 40m for NVIS, 20m with a good pattern and low take off angle, plus 10m and 6m. I might move the feed point to 40% and gain 15m coverage.

I got some mast sections from The Mast Company, plan to install with an apex eave mount. Put the Comet GP-15 on the top.

40m DX Option 1. The mast may provide a support for one end of a 40m Half Square. Will favor SW / NE which covers the Pacific, and Europe / Africa in the other direction. More info regarding half-squares:


Far field plot for the half square I modeled.

40m DX Option 2. Two element vertical Yagi using a single 60ft support, I got the idea from this page - http://dl2kq.de/mmana/4-3-35.htm. I have tweaked the geometry to bring it up to 7.15MHz.

I found additional information by N6LF - Getting the Most from Half-Wave Sloper Arrays.

There are perhaps 3 ways to feed this antenna:
  • N6LF settled on resonating both elements as reflectors, and end feeding the selected driven element - the parallel tuned circuit used to match takes care of resonating the driven element.
  • Borrowing from K9YC's End-Feeding a Center-Fed Vertical Dipole, the bottom half of each element would be made from coax with good chokes at the bottom which K9YC also discusses. Leaving one side open circuit resonates the element as a reflector - the length of coax is critical, I calculated (info below) there would be enough length to form the bottom half of the dipole, the choke and connections to switching relay. Some form of strain relief may be needed for the coax half of the dipoles to stop it from stretching.
  • Using the same principal as above but center feeding with coax (just like a conventional coax fed dipole) to a mast mounted switch that short circuits the inactive element creating a closed stub which resonates it as a reflector, the length needed is much shorter hence the mast mounted switch. A balun would be needed at the feed point which adds weight.

The latter two open/closed circuit stubs will present an inductive reactance lowering the resonant frequency of the passive element turning it into a reflector. How to figure it out? W8WWV wrote a nice article on Coaxial Cable Stub Q, which lead me to an application called Transmission Line Details. Among other things this can be used to calculate the length of open or closed stubs, it also tells you how much R the stub will add at the feed-point of the passive element - this information can be plugged into MMANA to know the effect of the added R.

Another handy calculator I found is Inductive Reactance Calculator, which converts an inductance at a given frequency into an inductive reactance value. Useful in conjunction with MMANA-GAL and TLD.

It's important to note that properties of coax varies between manufactures and manufacturing runs. The length is critical, one would need to measure the velocity factor of the coax on hand using an antenna analyzer, not rely on published information. I suspect this is the reason why some struggle to get phased arrays to work properly, relying on the publish spec is not close enough to reality.

Personally I think N6LF's end fed might be the better choice as it eliminates the weight of coax, baluns, mast mounted switches etc. If using high power, capacitors need to handle several kV. The only critical part is resonating both elements as reflectors.

From the model, I like this antenna for a couple reasons, it has a nice broad beam width, and 2 dBi of gain at 10 degrees elevation, the F/B is ok at 13 dB. It can also be built using a single support.

MMANA-GAL file for 40m 2 element vertical Yagi.


View of 2 element vertical, these are half wave dipoles with the ends angled towards each other. 


Far field plot for the 2 element vertical.


3D far field plot from GAL-ANA.

What I like about this is it can be built with a single 60ft support. Has good gain at low angles, 2 dBi at 10 degrees, -3 dB beam width is slightly more than 120 degrees.

40m DX Option 3. Update 08-Aug-19, attempted to build this with my 43 ft vertical, however the vertical is too flimsy to support the tension needed on the passive elements to get them into the right shape. I'd need to rebuild the vertical with longer sections (less taper) and guy it. I did enjoy the time spent researching this antenna, modeling it, and learned a few things along the way. I'm disappointed that I cannot make a good attempt at building this antenna. Maybe another day!

Another variation of vertical Yagi from http://dl2kq.de/mmana/4-3-35.htm is the 3 element GP80 scaled for 40m.

Very close resemblance to the Spitfire antenna developed by K1VR and W1FV - http://www.yccc.org/Articles/Spitfire/spitfire.htm. It also appears in ON4UN’s Low Band DX book, and N6LF's Single Support Gain Antennas for 80 and 160 Meters.

What I like about this is the 43ft vertical I already have with 32 buried radials is the right length for the 40m version driven element. Makes good use of what I already have in place. All I need to do is add the passive elements, and simple matching network with series capacitance.

This antenna design is kinda neat on a few points:
  • The driven element is around 1/3 λ this raises feed-point impedance to a convenient 50 Ω, and can be adjusted as needed to be 50 Ω, series capacitance takes care of bringing it to resonance
  • The extra length also supports the passive elements and their shape, can double as guy lines.
  • The passive elements are 1/2 λ and folded (and thus independent of the ground plane), shortening one via switch/relay in the low horizontal section turns it into a director, direction could easily be made electronically reversible.





View and far field plots of the 3 element GP.

MMANA-GAL file for 3 element GP 40.

Since I have the driven element already in place, modeling it by it-self showed feed point being 70Ω, jX 108 at 7.15 MHz. I went and measured it with the analyzer and to my surprise it's very close:



Analyzer shows 72Ω, jX 104, along with the series capacitance needed for resonance - 213pF. Adding series capacitance of 200pF to the model brought it to resonance. The test and result is encouraging.

What to do for 80m due to space and tree locations, I've considered many different possibilities. The best solution I can find is a quad loop squashed into a rectangle. Feeding from one of the sides results in bi-directional low angle vertical polarization. An 160m version of this antenna gets a mention in Low-Band DXing 5th Ed - Chapter 10, pages 4 and 5.

At the other end of the spectrum, the 7 element Yagi I have in the attic for 900MHz is sub-optimal, need to relocate it or try something different.