StackMatch for two antennas by T93M

 

There are  few products available to HAM community and all of them are very sophisticated tools. Some of them are able to switch up to four antennas in phase (stacks) and even out of phase to produce high elevation angle of radiation.

All of the available products are remote controlled, meaning that switching box is somewhere on the tower in order to phase two or more antennas for additional gain and lower take off angle (TOA. 

What about two antennas on separate towers or two antennas with different polarizations?

It is known that some contesters are using two antennas pointed to different directions in order to maximize their results. Some stations are equipped with two antennas for one band but different polarization. 

My idea was to make my own two antenna switch being able to match two antennas in parallel. This is very useful on 80m band in Europe where high TOA is needed for short distance contacts with European stations and still being able to utilize antenna with low TOA to be heard across the Atlantic or far east. As well it is very useful for Caribbean stations to point one antenna to closer US territories and other to Europe in order to maximize the score.

Some stations are simply using two amplifiers exiting two different antennas but this practice has limitations not to mention that using two amplifiers with 1500w output to each antenna  is against rules in most international contests.

Well, my antenna StackMatch is not remote controlled and is made to sit next to the rest of the controls (i.e. rotor, antenna switches etc.). This way there is flexibility to rearrange cables and antennas during the contest without climbing the tower and loosing the precious time on the radio. 

StackMatch is very simple switching device which is consisted of three 10 A  DPDT relays and 2:1 UN-UN (unbalanced to unbalanced) transmission line transformer. As well there is 3 position rotary switch and LED's as indicators.

I spend some time trying to figure out how to accomplish switching three combinations and still to be able to insert 50:25 Ohm transformer in third position with three relays. Because of specific rotary switch on hand I needed third relay even though it can be done with only two relays. Well I succeeded and it can be seen at schematic diagram (sorry still working on it).

 I have experimented with few ferrite cores and different number of turns until I have succeeded to have StackMatch work from 1.8 to 30 MHz with VSWR less then 1.2:1 in position when two identical antennas are connected. There is also 40 pF /12kV capacitor (two 80 pF/6kV in series) across output of transformer (25 Ohms) to cancel inductive reactance from windings on ferrite core. In order to test and tune this device  I have used CIA-HF antenna analyzer. 

StackMatch was tested on the bench with 1500W into two 50 Ohms dummy loads. During one minute key down core and windings were cold as well as capacitor indicating almost no loss. I was not able to measure total loss of this device due to lack of instruments but I think the loss is negligible. 

 Most of the parts can be purchased in Radio Shack although same components are somewhat cheaper if you order them online from Mouser Electronic.  

For more info or help to build this simple device by yourself feel free to contact me at my email: T93M_at_T93M.com