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Feeding 1/4 wave vertical - how are you doing it?

For those of you using a single band resonant vertical consisting of a 1/4 wave vertical wire supported by a fiberglass pole plus radial (counterpoise), how are you feeding it? Do you feed directly with coax, do you use some sort of unun xfmr (please describe), do you use a coax choke (air wound or toroid wound?) etc etc???

Thanks & 73,
Barry N1EU

Good question Barry! I’m sure you’ve just taken the lid from a can of worms :wink:

Personally I feed mine straight from the coax and it appears to work fine, I use four radials.

The SOTAbeams vertical system (no longer available) used the standard choke at the base - several windings of the RG-174 through a ferrite core.

Interesting to see what the wisdom is!

73, Colin

Interesting

Mine is 11m of wire going up me 8m squid pole with 3m of it coiled on the plastic pipe i have on the squid pole 5m up using sota wire for 40mb .

Fed via a home made 9:1 Unun and counterpoise wires x4 = total length equaling 1/4w of 40mb and then RG8X mini to the MFJ949 and rig. Tune,s all bands 80m to 10m

Mine works well first contact was VK5PAS off kit hill G/DC-004 on 10w with a single counterpoise wire 11m, long then changed it to 4 lengths of wire by cutting the 11m wire into 4 equal lengths

works for me :slight_smile:

Where i got my idea from and built myself.

karl m3feh

Karl, Barry is asking about feeding a ¼wave single band antenna, what you have there is a completely different animal!

The feedpoint impedance of a ¼ wave should be quite low - in some cases above 50 ohms, some cases below 50 ohms.

The problem may arise that the coax outer effectively becomes another radial in the system without some means to stop the RF at the antenna feedpoint. An impedance transformation should not be needed.

73, Colin

I have a quarter wave vertical for 20m attached to a 7m fibreglass telescopic pole. At the feedpoint I have 3 radials, each 5.02m long, and the feedpoint is about 1.5m above ground level. The radials each have a section of cord at the distant end acting as an insulator, so the ends are in the air and not connected to ground in any way. I feed this with RG58 50 ohm coax, with no transformer, balun or unun. Its feed impedance is such that the measured SWR is about 1.1 on 14.1 and it rises slightly at 14.3 but not enough to affect the transmitter output power.

This antenna has provided many SOTA dx contacts using 10w of output power from an IC703, mainly European long path contacts.

73 Andrew VK1DA/VK2UH

No transformer of any kind. You don’t need one. Feed it directly. Cut the main element down to tune against the CP.

One of the simplest, easiest and most effective DX antennas one can put on a fishing pole IMHO. My log agrees !

Jonathan

Mine is a 1/4w 40mb vert antenna but 9:1 unun is there so one can tune in the other bands i desire.
Also got a 1/2w 40mb antenna again unun to aid tuning in other bands

Single band ok, but like to explore the HF and not restrict myself to one band and less messy with only one antenna to do me job for me :slight_smile:
|Karl

I agree entirely. For my activations in Portugal I constructed a coaxial choke made with RG-174 to stop the RF coming back down the coax. I use a small 5m pole and feed the 14MHz 1/4 wave at just above ground level and deploy two radials (or should that be counterpoises - we’ve had that debate!). Before I constructed the choke I received some quite vicious RF burns off my straight key, even though the rig was just an 817. Bizarrely, I don’t seem to have the same problem when using the antenna in Scotland which must be something to do with ground conductivity. :slight_smile:

Gerald G4OIG

As per Jonathan, my 12m 1/4wave GP consisted of 1/4wave vertical radiator and 3 of 1/4wave radial drooping at 45degs. It was fed direct with 3m of RG58 from the 817. I needed to adjust the vertical section marginally from 1/4 to get the match to 50ohm +/-. The radials ended in bulldog clips and were clipped to the guy cords. It all fitted on a 5m mast.

One of the reasons for a 12m challenge was I could fit a DX magnet of an antenna on my existing mast without buying any new equipment! Hey, there has to be some advantage for helping to run the scheme :wink:

Thanks for all the responses!

I’m thinking of a choke balun at the feedpoint consisting of an FT82-43 or FT114-43 ferrite toroid and 5-7 turns of my RG174 through it. That should give 1000-2000 ohms common mode impedance.

73, Barry N1EU

Sounds good to me Barry!

I suppose that feedline length will be a factor too. I used a 1m patch lead from the antenna base for VSWR trimming, once I’d finished, I used 25m of RG-213 to connect the antenna to my rig. The antenna was built for 18MHz.

I wonder what would happen if fed without a choke and using a feed line length more closely related to the frequency of use?

I think the use of a common mode choke is a sensible idea.

73, Colin

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I think you’re right Colin. Without a choke, results may vary based on feedline length.

73, Barry

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Not matter how many times you call it a 1/4wave for 40 it’s not. 40/4 = 10m and your radiator is 10% too long. It’s not a 1/4wave for 40m with that length or radiator, those lengths of radials or that set of angles. A 1/4wave is resonant and can be setup so it doesn’t need any matching to 50Ohms.

You antenna is some random length end-fed with assorted impedance lowering (the 9:1 unun) and impedance matching (MFJ949).

It works as you have had an S2S with VK which is fine and dandy. But that still doesn’t make it a 1/4wave for 40! :slight_smile:

Yes Karl your antenna is interesting! An electrical quarter wave of PVC insulated wire at 7.1MHz is approx. 10.2m long, then you’ve got that coil in the middle which will add some inductive centre loading so I wouldn’t be surprised if it actually resonates around 60m :wink: (would be interesting to actually check the resonant frequency)

If it were resonant on 40 with an impedance around 50 ohms or probably less, by the time you’ve allowed for the Unun you’d be down around 5 ohms at the feedpoint which I guess your ATU would struggle with so it’s probably a good job :smiley:

I use a similar rationale for the doublet I use for most activations - it’s a bit longer than resonant on 60m, but gives very convenient settings on the ATU on 80, 60 and 40 :slight_smile:

Whatever it is, what matters is that it works :smiley: :smiley:

73 de Paul G4MD

The one I have is fed directly from the coax but it is best to use a good choke 1:1 Balun to isolate the Coax shield as already said

73 Angel

Hi Karl,
In my case I’ve always fed my about 7m long random wire directly from the inner conductor of my RG58 coax and the radials connected directly to the coax braid.

I wouldn’t care for any possible RF radiation through a few meters of coax line we usualy have in the summits or even for any possible RF return while we are transmitting QRP.

Cheers,

Guru.

i also transmit with 10…100W and feed the vertical (10m long) direct, without any filter, balun or unun. i had not any problems yet.
my packpack with the TRX (alinco dx sr8) stands direct close the vertical, no coax between antenna and tuner. no promlems any time :slight_smile:

73!