M0BZI HF10 Doublet
I have rather a limited area to put up any aerial, its around 45 feet deep and 18 feet wide. Im surrounded by buildings three storeys high with BT lines all around. In fact next door extended back the whole length of plot!! Only positive point is that the guttering is around 28 feet high and I have managed to get a pulley onto the wall so can use this height! The local daylight noise level is high S7 on 40m to S2 on 10m & once night comes, the local street lights add to this. OFCOM have put it down to the local community “radio fog” that comes from the houses as it disappears at the end of the garden!!
Limited space
I came across Fred Westerns aerial and a Google brought up the reviews on e-net
A read through these and a quick check of Freds QRZ.com page gave me more info. Its very basically a doublet with a top length of 67 feet and a length of 450 ohm ribbon to a current balun. In basic form, it’s a half wave G5RV with loading coils to give full coverage from 160-6m! the balun appears to be a 4:1 current type.
I measured up the space and reckoned rather than putting it up as a Inv Vee sloping dipole, if I used a couple of telescopic fibreglass poles I could get the main legs up almost horizontal and Avenge height of 18 feet! So I bit the bullet and ordered one via email and Paypal! Within 2 days it had arrived.
First Thoughts:
It arrived via sign for mail. It was well packed within a jiffy bag. The fixings are all stainless steel and the wire is lovely Flexweave so very weather proof. The 15’ 3’’ slotted ribbon wire is very hardy. The balun is well made and the loading coils are also well made and covered by heat shrink so should be ok in the weather up here!!
Up it goes
I took down my OCFD and laid out the doublet. When using the ribbon cable, you must try to keep it clear from anything so I worked out I could keep the main run about eighteen inches away from the wall and earth to keep the aerial currents balanced.
I raised up the doublet, with the legs not as sloping as before as I used a couple of telescopic fibreglass “camping” flagpoles. I removed the top 3 sections to make it sturdier and thus put the legs around 17 feet up. One leg is dog legged down and across the garden then down towards ground the other drops to the pole then again to earth. So my lie out is less inverted than sloping. The feed drops parallel to the drain pipe and trying to keep it out. I have to use extra thin coax (RG174) to go through the window so I connected up a short run (OK it’s a bit lossy but over the 3m run its hardly anything!). I wound a choke just after the 4:1 balun and also used another ugly choke just before the ATU.
Findings
Firstly the background noise didn’t drop (Damn!!) and signals were heard on most bands even if conditions at the mo’ is not good
I charged up the batteries for my MFJ259 and checked the calibration before using to check out this aerial.
The following figures were taken at the ATU feed point at the aerial side:
How did it work?
Well the noise level didn’t drop much and I was able to tune it on all bands using my MFJ-969 ATU. Band conditions are not too good but hearing some good distance signals. I am getting out on the bands I have tried it out on. I know my working situation is not that good & it should work in a better clear location!
Looking around at wire aerials, the cost and build are good value. OK you could buy a ½ G5RV loading coils & a balun for maybe less. But you could buy more expensive wire aerials. Its going to stay up over winter and maybe the bands will re-open??
For those of us wanting to work all HF bands in limited locations and wanting a low visual impact aerial and not wanting a vertical (with no room for a decent radial system) this could be the answer!
This article was kindly submitted by Chris G4LDS
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