Re: Wimo 13cms yagi

John Quarmby

The older Andrews FHJ4-50, a predecessor to LDF4-50, has helical corrugation of the outer, very obvious when you inspect the interior of the connectors used on it which are also helically grooved. I think it dates back to the late 70s, so not seen much these days.


John G3XDY

Sent from my Samsung Galaxy smartphone.

-------- Original message --------
From: "alwyn.seeds1" <a.seeds@...>
Date: 16/11/2019 10:23 (GMT+00:00)
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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