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nov 3

Loop detected, SWR 1.1 but S9+ noise and no signals

5 commenti

I fear I’m missing something very simple. Connections are antenna into atu and atu into radio. No cat etc as yet as I’d like to get the antenna working before I add complexity.


can anyone help troubleshoot please?


antenna is mounted on a rotator cage from my mast and at least 1.5m above ground (baby loop)

nov 4

Hi, Jim,

Let's first make some checks. With the Ciro-Mazzoni controller in the RECEIVE state, or powered OFF, there should be a direct DC connection between the centre pins of the rear ANTENNA and RADIO sockets. Use a multi-meter on the OHMS range to check. This verifies that the internal antenna change-over relay is working in the receive state. Make sure that it is also true when the controller is powered up, but not tuning. Connect the loop antenna cable to the ANTENNA socket, and the radio cable to the RADIO socket. Tune the radio to a suitable frequency, for example 14.175MHz, and manually tune the loop to the same frequency. You should hear the tuning signal in the radio at well over S9, and the loop should tune to this frequency and stop with an SWR of less than 1.5:1. When the controller stops tuning and switches back to the receive mode, you should now hear signals or band noise. If your transceiver has several antenna sockets, make sure you have selected the active one - don't laugh - I spent more than an hour tracking down a 'faulty' antenna only to discover that my antenna selection was incorrect! If the antenna tunes correctly, and can automatically detect your antenna, then the controller and antenna connection is OK, and the fault must be between the RADIO socket and the transceiver.

73, Adrian, 5B4AIY

7 giorni fa

Thank you Adrian, as always for your very considered and detailed reply! I was out reading for a Foundation license exam yesterday so was unable to get into my shack after work.


Tonight I will disconnect everything and test my patch cables, double check the two SO239 connections are correct on the ATU and try again. I'll also ensure I'm connecting to ANT1 on the 7610.


Feedback to follow!

3 giorni fa

So... I replaced and tested all coax and tested the ATU and all checks out ok. One thing that would be worth confirming Adrian- do you know whether there should be a short between the centre and shield of the coax on the loop itself? I wasnt sure whether any balun arrangement within the antenna may cause this. I have a short in this coax however.

14 ore fa

I confirmed that the gamma match would cause a short on the attached coax... brand new coax and patch leads all round but no difference.

One thing I need to do is get the loop off the rotator cage etc and move to a different location. My old mast base that it utilises at present has rebar etc. in it so that may well be the issue...

10 ore fa

Hi, Jim,

If you measured a short circuit from the antenna cable to the antenna, and the controller can both automatically detect and tune the antenna, as I said in previous post, this proves that the connection from the ANTENNA socket and the control cable socket to the antenna is good. OK, what you now need to do is tune the antenna to a frequency, such as in the 40m band where you can be certain that there are signals, and when the antenna controller has tuned the antenna, disconnect the cable from the ANTENNA socket and connect it directly to your transceiver - you should be able to hear band noise and signals, and you should be able to tune +/-5kHz from this frequency and still hear strong signals. If the problem still persists, then the noise is definitely being picked up at the antenna, and if it is the same as when the cable is connected to the controller and the radio connected as well then you will have to try and re-locate the antenna or else try and find where the noise originates. What sort of noise? Any plasma TVs, switch-mode power supplies, etc?

73, Adrian 5B4AIY

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