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.