[TowerTalk] 80 m 4-square high SWR with no obvious reason why - using COMTEK ACB-80

[gwj at me.com]

1. Dump power is the most crucial diagnostic. It will quickly rise with any significant mismatch in the array. The quadrature hybrid matching system tends to minimize SWR fluctuations even when one or more array elements are not well matched. So having high SWR means something terrible is indeed wrong.

2. Is your dummy load on the dump port ok? If if was undersized, a severe mismatch would likely fry it.

3. Measure the impedance looking into each phasing line with all the others disconnected. The absolute value is perhaps less important than seeing that they are all nearly equal over the bandwidth of interest. That can quickly lead you to a failed element. Keep a record of this data!

Though I haven’t seen it happen, it is of course possible that one of the transformers or a relay could be damaged in the switching box.

If you have a common-mode choke at the feedpoint of each antenna, it’s possible for that to overheat during the time power was applied with a dropped element. Voltage across the choke can become very high and power dissipation goes out of sight. If severely damaged, the choke may cease to function, leaving the outside of the phasing line shield “connected" to the radial system, which alters the feedpoint impedance and array pattern.

Gary Johnson, NA6O
gwj at me.com
https://na6o.com

> On Jun 27, 2022, at 9:00 AM, towertalk-request at contesting.com wrote:
> 
> What is striking to me is that the forward power has uniformly dropped 
> and the reflected power has uniformly risen across the entire band as 
> though the entire array was detuned by 500 khz, suggesting something 
> systemic.  I suspect that the problem is in the relay box but I can't 
> figure out what may be causing this.
> 
> Has anyone experienced a similar problem with their ACB-40, ACB-80 or 
> ACB-160?  Does anyone have any idea of what to do look for next?
> 
> Tnx & 73
> 
> Bob, KQ2M