Sunday, September 22, 2019

43ft Vertical 80m Matching

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.

Some more progress on the matching network today. Relays mounted but not wired, and redid the antenna connectors with a copper plated steel strip (found in the plumbing section at Lowe's) for better grounding.