Hy-Gain AV-640 Problem

[DRBComm]

I finally acquired my first HF rig (IC-7300) and got it hooked up to my Hy-Gain AV-640 which came with the house that I bought (a nice bonus).

The problem is that I am not receiving many signals and when I try to transmit, I get an infinity SWR. So during troubleshooting of the matching unit, I have noticed a 'short' between the center and threaded portion of the SO-239 connector. I want to know if this 'short' is by design or is there something wrong with this box?

Thanks

 

[tweiss3]

Is the short on the coax/antenna side or the 7300? On the coax, it should not have a short.

 

[DRBComm]

Is the short on the coax/antenna side or the 7300? On the coax, it should not have a short.

The short is at the matching unit SO-239 with no feed line connected. It is also worthy of noting that the feed line itself does not short either, just the connector at the matching unit.

 

[prcguy]

I believe that antenna will show a short across its input connector.

 

[techman210]

From the manual:

"The AV-640 is DC grounded for static discharge. This is accomplished with a choke coil
in the Matching Unit. This coil could fail under high voltage spikes from a near or direct
lightning strike"

 

[DRBComm]

From the manual:

"The AV-640 is DC grounded for static discharge. This is accomplished with a choke coil
in the Matching Unit. This coil could fail under high voltage spikes from a near or direct
lightning strike"

Any idea what a 'failure' would look like?

 

[techman210]

I would open the unit up and look for a burnt coil but that probably isn’t going to be the problem.

Likely something in there that is shorting something out that shouldn’t be shorted. Probably a capacitor in there that is shorted or bad. Insects like to build nests in places like that.

This should help:

AV-640 (Evaluation, Wasps, and Repair)

Good luck

 

[prcguy]

I would hit it with an antenna analyzer to see if it resonates anywhere and if so is it near ham bands. That would point you to either something broken or just put together wrong.

 

[DRBComm]

I would hit it with an antenna analyzer to see if it resonates anywhere and if so is it near ham bands. That would point you to either something broken or just put together wrong.

My friend did that already. He checked SWR on 20 and 40 meters, received infinite SWR on both with the Rig Expert AA30

 

[prcguy]

My friend did that already. He checked SWR on 20 and 40 meters, received infinite SWR on both with the Rig Expert AA30

I think the problem is in the match box. I believe the antenna is an end fed with high ratio transformer like a 49:1. If so you might be able to disconnect the antenna and test the match box with a resistor around 2.5K ohms on the secondary.

 

[DRBComm]

I think the problem is in the match box. I believe the antenna is an end fed with high ratio transformer like a 49:1. If so you might be able to disconnect the antenna and test the match box with a resistor around 2.5K ohms on the secondary.

Can you please elaborate on your instructions? I have included a picture so you can tell me where to test the unit. This is a great learning situation for me.

 

[prcguy]

Can you please elaborate on your instructions? I have included a picture so you can tell me where to test the unit. This is a great learning situation for me.

The coil of brown coax (RG142) is a common mode choke at the 50 ohm input and the black/white wire coil should be the transformer and possibly a 49:1 ratio. Connect an antenna analyzer to the 50 ohm input and a 2.5K ohm resistor across the transformer output and see what the VSWR is And it should be very good if everything is workin. The little choke is for static bypass and will usually be across the transformer output. The blue capacitor may be for matching on the transformer.