Re: Wimo 13cms yagi

John Lemay

Hello Alwyn


I’m interested in your comment about connectors because very recently I had a problem with what looked like, at first sight, a decent quality 50ohm N type termination (male):


It showed a good return loss to around 2GHz, becoming very poor (-6dB) around 2.5GHz and then improving significantly above that frequency. Is that what is called “suck out” ?


On inspection I decided that the pin was making good contact and so was the screw ring. But the more important inner fixed ring was sometimes not making contact – which I proved by carefully making it slightly oval – problem (crudely) solved.


It makes me consider that plugs that have the inner ring split into “fingers” are a better bet ?







From: [] On Behalf Of alwyn.seeds1
Sent: 16 November 2019 10:23
To: UK Microwaves
Subject: Re: [UKMicrowaves] Wimo 13cms yagi


Dear All,


Cable and connectors.


I have measured very deep (20dB) suck-outs and corresponding reflection spikes around 2.3GHz on some samples of Ecoflex 15.


I have also measured severe suck-outs, but usually above 3 GHz, on poor quality N-Type connectors.


Definitely check your cable and connectors carefully, before working on the aerial.


Regarding the comment on “Heliax”, I do not agree. 


All foamed dielectric solid outer cables that I have seen do not have helical corrugations.


I have measured many samples of these cables up to their rated frequencies and above.


The large LCF-78 types are rated to 6GHz and have no problems at all at 2.3GHz.


The upper frequency limit is normally set by circumferential modes in the cable- the spacing between the corrugations is chosen so that the periodic feedback from these occurs above this frequency.




Alwyn G8DOH





Alwyn Seeds, Director
SynOptika Ltd.,
114 Beaufort Street,
SW3 6BU,

SynOptika Ltd., Registered in England and Wales: No. 04606737
Registered Office: 114 Beaufort Street, London, SW3 6BU, United Kingdom.



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