Is a metal ring and U, wire loop strain relief unhelpful capacticance or LC ?

RadioDXfun

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Joined
Dec 14, 2021
Messages
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Location
United Kingdom
Like most people who use a long wire/EFHW my antennas have a a strain relief on the transformer plastic box. I started to wonder
how this might affect the antenna. A looped piece of wire with insulation looks a lot like a capacitor to me.

So I have removed the strain relief which I do not need really and instead Gorilla glued the wire to the box itself rather than have that loop
of wire. I suspect that the higher in frequency the greater the effects of that loop on the antenna tuning. (as that loop becomes a greater proportion of the radiating element) On an EFHW (at actual half wave freq of the wire) there are high voltages at the ends of the antenna. As such I thought it was an odd place to have what is in effect a capacitor or some kind of extra LC circuit (a loop and a capacitive effect).

So I expect my VSWR to change a little but I do wonder if this will have an effect on pattern or match.

I cannot quite work out what effects it might have or not have so any input appreciated.

Anyway I have always looked at this arrangement and though that does not look great to me. (Albeit great for strain relief)

This is a random internet find, nearly all of these antenna types that hams DIY use it, myself included
until now that is. I also wonder if doing away with the strain relief would potential help any SWR issues for multi band users.
I only use mono band cut ones myself so a non issue for me personally.

cap.jpg
 
Last edited:

prcguy

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So Cal - Richardson, TX - Tewksbury, MA
The loop is a very tiny fraction of a wavelength even at 10m, I don't believe it has enough effect on anything to worry about. It also has two wires going in opposite directions which can cancel the effects of whatever the loop at the end is doing. Even if it did affect resonance the antenna is tuned at the factory or by the maker to resonate on the desired bands, so any minor fraction of inductance is part of the tuned length.
 

RadioDXfun

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Joined
Dec 14, 2021
Messages
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Location
United Kingdom
Thanks prcguy, I suspected it may not have a great influence but have always looked and wondered. I am off out to test this change I will jump on 15m with a 1/2 wave vertical within about 1-1.5 hours from now at a good portable QTH SSB phone. If you hear a portable 15m band station from the UK it may well be me, a bit of sunset DX. The VSWR is usually 1.3:1 typically so I see if it has changed at all.
 

RadioDXfun

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Joined
Dec 14, 2021
Messages
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Location
United Kingdom
It dropped the SWR to a 1:1 match on the radio meter, once my antenna was at its usual height. (after a slightly breezy start was 1.1:1 at 3m lower than normal) So I will leave it as it is. Nice DX evening 15m band contacts made from UK. Indonesia, multiple USA including California, Nebraska (or Montana as per QRZ), Montserrat. Just to avoid confusion this is a home brew 1/2 wave monoband cut antenna.

It certainly did no harm.
 

RadioDXfun

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Joined
Dec 14, 2021
Messages
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Location
United Kingdom
I have changed all 3 of my mono band cut EFHW's to "no loopers" (and with a croc clip extension they mono band me for 20/17/15/12/10) I have never liked the look of that method and I do not really need a high level strain relief as I use them all vertical. (Gorilla glue blob does the job well enough) I insulating tape the driven elements / transformer box onto the fibre glass pole so the weight is never pulling very hard on the element itself

I have limited antenna options so all my focus goes on making what I do use as close to perfect as I can for the way I use them.
 

W5lz

Active Member
Joined
Feb 28, 2019
Messages
603
Like most people who use a long wire/EFHW my antennas have a a strain relief on the transformer plastic box. I started to wonder
how this might affect the antenna. A looped piece of wire with insulation looks a lot like a capacitor to me.

So I have removed the strain relief which I do not need really and instead Gorilla glued the wire to the box itself rather than have that loop
of wire. I suspect that the higher in frequency the greater the effects of that loop on the antenna tuning. (as that loop becomes a greater proportion of the radiating element) On an EFHW (at actual half wave freq of the wire) there are high voltages at the ends of the antenna. As such I thought it was an odd place to have what is in effect a capacitor or some kind of extra LC circuit (a loop and a capacitive effect).

So I expect my VSWR to change a little but I do wonder if this will have an effect on pattern or match.

I cannot quite work out what effects it might have or not have so any input appreciated.

Anyway I have always looked at this arrangement and though that does not look great to me. (Albeit great for strain relief)

This is a random internet find, nearly all of these antenna types that hams DIY use it, myself included
until now that is. I also wonder if doing away with the strain relief would potential help any SWR issues for multi band users.
I only use mono band cut ones myself so a non issue for me personally.

View attachment 121003
" I also wonder if doing away with the strain relief would potential help any SWR issues for multi band users. " ... N0.
 

W5lz

Active Member
Joined
Feb 28, 2019
Messages
603
" I do wonder if this will have an effect on pattern or match." ... pattern, no. '' SWR"... not much.
 

RadioDXfun

Member
Joined
Dec 14, 2021
Messages
11
Location
United Kingdom
The change to SWR was small but positive. As mentioned I like to try and perfect every detail of my small station. I think that
when you make many small seemingly insignificant changes they add up to a sum greater than parts. It gives you a "firing on all cylinders"
feeling, and if doing radio is not about feeling good what is it ?

Sure, conditions will make mince meat of your carefully minimized system losses/gains.... but when you are regularly working DX at S0 R4/R3 it makes you glad you bothered.
 
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