Re: Wimo 13cms yagi
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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: UKMicrowaves@groups.io [mailto:UKMicrowaves@groups.io] On Behalf Of alwyn.seeds1
Sent: 16 November 2019 10:23
To: UK Microwaves groups.io
Subject: Re: [UKMicrowaves] Wimo 13cms yagi
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 Seeds, Director