The making of a dipole

[Quebec337]

Hi there,

I'll soon be doing a dipole antenna for my receiver (Icom R-9000).
I had a lot of help on other forums here. I know basically how to make my antenna, but there is just one small detail I'm not sure about : what do I do with the braid of the coax, on the receiver's side ? It's connected at the junction of the "T", but what about the other end ?

Thanks,
Matt

 

[wbswetnam]

I assume that you are making a simple center-fed dipole... yes, the braid of your RG8X or whatever you are using will connect to one leg of the dipole, and the other end of the feed cable will connect to the shield of your PL-259 plug.

 

[Quebec337]

The plug of the receiver will be an RCA plug, so I'm not sure on how the braid is gonna connect to that.

 

[wbswetnam]

The plug of the receiver will be an RCA plug, so I'm not sure on how the braid is gonna connect to that.

I've never tried to attach an RCA plug to a feed cable, but somehow the braid has to make electrical contact with the outside flanges of the plug.

Instead of a simple center-fed dipole, you might want to consider something which will give you much more band coverage by using an off-center fed dipole, also sometimes called the "Carolina Windom". I have one in my back yard. It is simply a 4:1 voltage balun like this one ( https://www.amazon.com/Jetstream-JT...=1501258920&sr=8-4&keywords=4:1+voltage+balun ), with one leg of the dipole measuring 25 feet in length and the other measuring 45 feet in length. Suspend it from some tree branches in the yard (the higher, the better).

 

[wbswetnam]

I just looked at the specs for the ICOM 9000. It has an SO-239 input jack, to which you can connect the PL-259 (male) plug. A PL-259 is far superior to an RCA plug.

 

[Quebec337]

Yeah, you're right.

I was stuck on the idea that I would still have to use the RCA jack (which I'm doing with my longwire antenna now). So basically, at the receiver's end, the braid comes crashing inside the PL-259 plug, without never touching or coming in contact with anything else ?

Matt

 

[popnokick]

Yes... the braid should be soldered (or crimped) so as to make contact ONLY with the outer shell of the PL-259 connector. No part of the braid should touch the center conductor, or you will short out the signal. There are many websites explaining how to attach a PL-259 to coaxial cable. ALSO - Agree completely with wbswetnam regarding using an Off-Center Fed Dipole rather than a standard dipole with equal length legs. You'll get a much greater frequency coverage span by doing that. Read about Windom, Carolina Windom, or Off-Center Fed Dipole and how they work. I have one that is 283 feet long and covers 160 meters all the way up to 6 meters.

 

[Quebec337]

Well actually, my longwire antenna (quite simply and a little akwardly made, I suppose) is a approx. 100 feet long and 30 feet at it's highest point. Talking about "off center"....hehehehe....mine is kinda 90 feet or so on one side, and around 10 on the other. So it's a very unequal "T". All the wires are soldered together at the junction of the "T"....I found out lately that it was not really the way to do things Anyway...

Well, the project I had at first was to build one for one very specific frequency, with the calculations and all.

Would you say your off center fed dipole could do for a frequency practicaly the same job as an antenna lenght-built for the same very very specific frequency ? (Sorry, I'm french speaking....There might be some funny phrasing from time to time )

Thanks,
Matt

 

[popnokick]

The "off-center" part refers to the fact that the feedpoint is about 1/3 of the way from one end of the total length. The overall length determines the total frequency range covered. For transmitting there will be a series of resonant "sweet spots".... mostly in/near the ham bands. But for receiving it is VERY broad. Besides using mine to transmit with my Icom 7100 I am an avid utility listener and make a lot of use of my IC-7100 for things like MWARA air route comms, military, maritime, and other utility stations. The OCFD works very well as a "general coverage" antenna.

 

[Quebec337]

Ahh.....interesting

I'm personally very fond of those pacific hard to get catch...

So to conclude, considering the fact that my actual antenna is "off center" by more than 90 %, and given that here are no insulators at the junction of the "T" : is it worthwhile to "refurbish" (coax, insulators) or do you think a new one would do way way better than the one I have now ? In other words....is 90% too much off center, in your opinion ?

Matt

 

[majoco]

https://m0ukd.com/homebrew/antennas/homemade-carolina-windom-antenna/

 

[popnokick]

majoco - Thx for the link. MATT - be sure to scroll down the page all the way and look at the pics. Excellent detail of how you make the connections to each "leg". And you DO need an insulator at the junction of the "T"... where the balun goes. Also, pay attention to the ratios shown. They are not random, and 90% is not correct. The webpage's author very correctly notes, "Holding true to the original Windom formulas, I used a ratio of 37.8% for one side and 62.2% for the longest side after determining the half wave length at the lowest operating frequency…. This is the 200Ω point, hence the 4:1 balun. (50Ω to 200&#937"

 

[wbswetnam]

....is 90% too much off center, in your opinion ?

Yes, it is. I'd cut that 90' leg and chop it in two lengths of 60' and 30'. Since you are wanting to receive only and not transmit on this OCF (off-center fed) dipole antenna, the precise lengths are not quite as important as it would be if you were trying for good SWR on the HF amateur radio bands.

That said, however, you might want to go ahead and make this antenna usable for amateur radio if you ever decide to become a 'ham'; ergo, make those lengths 34' for the shorter leg and 56' for the longer leg. Actually, I get very good band coverage with my 45' / 25' OCFD. I can get 40m, 20m, 10m and 6m with it (but not 15m, the SWR is too high).

 

[Quebec337]

Yes, it is. I'd cut that 90' leg and chop it in two lengths of 60' and 30'. Since you are wanting to receive only and not transmit on this OCF (off-center fed) dipole antenna, the precise lengths are not quite as important as it would be if you were trying for good SWR on the HF amateur radio bands.

That said, however, you might want to go ahead and make this antenna usable for amateur radio if you ever decide to become a 'ham'; ergo, make those lengths 34' for the shorter leg and 56' for the longer leg. Actually, I get very good band coverage with my 45' / 25' OCFD. I can get 40m, 20m, 10m and 6m with it (but not 15m, the SWR is too high).

Ok, 90' (60' on one side, 30' on the other), the coax, the insulators.....it's all feasable for me. Thanks !
Although, a "balun", a "choke"....it's all new to me. Is a balun a must ? It seem like one awnser always brings 2 more questions....how all these things connect. Anyway, I'll certainly be back with more questionnings Now, I'll do my homework the best I can.

Matt

 

[WA8ZTZ]

Quebec,

What frequency or frequencies are you interested in receiving? A Windom will have wider coverage than a dipole but there are better choices for general coverage HF.

My suggestion would be to look at the PAR EF-SWL antenna for HF coverage. Connect it to the SO-239 input. Make sure the slide switch next to the SO-239 is in the "ant-1" position. For VHF and above, get a discone antenna. Connect it to the inboard N connector (via an adapter if your coax terminates in a PL-259).

The R-9000 being a wideband receiver requires the use of at least these 2 antennas to get full use out of it. No one antenna will be sufficient.

Enjoy your R-9000... nice RX !

 

[majoco]

IMHO the PAR EF-SWL is not much more than a bit of wire with a 9:1 balun on the end - get a look at this.....

https://m0ukd.com/homebrew/baluns-and-ununs/91-magnetic-longwire-balun-unun/

 

[WA8ZTZ]

IMHO the PAR EF-SWL is not much more than a bit of wire with a 9:1 balun on the end

Not much more than 45' of wire and a matchbox but it works. Got two of them here and in a side by side comparison with various of my other antennas ( horizontal, sloper, and verticals) the PAR EF-SWL generally outperforms them all. The exception would be if the other antenna were cut for a specific frequency then it would have the advantage over the EF-SWL at that frequency range. The EF-SWL performs well from longwave through AM broadcast band and all the way up to the upper HF region. Not many antennas can do that. Being end fed makes it easy to use. Anyway, FWIW, just my suggestion to the OP for a simple, effective antenna.

btw, tnx for the 9:1 balun info

 

[ridgescan]

Not much more than 45' of wire and a matchbox but it works. Got two of them here and in a side by side comparison with various of my other antennas ( horizontal, sloper, and verticals) the PAR EF-SWL generally outperforms them all. The exception would be if the other antenna were cut for a specific frequency then it would have the advantage over the EF-SWL at that frequency range. The EF-SWL performs well from longwave through AM broadcast band and all the way up to the upper HF region. Not many antennas can do that. Being end fed makes it easy to use. Anyway, FWIW, just my suggestion to the OP for a simple, effective antenna.

btw, tnx for the 9:1 balun info

I run a PAR trans box to a 100' wire instead of the stock 45-footer. It is grounded to a copper aerator pipe at roof level that I tested for ground. This thing is way better on SW than my Wellbrook loop, and I would take your claim of it doing well in upper HF to it even does very well in VHF low! I get the entire bay area CHP in 42megs, San Francisco being the strongest at +30 over 9. It also does fantastically in MW and LW so yes it is quite the widebander in my experience. So to the OP, I would advocate for a PAR endfed over that dipole for receive any day. Although I never have tried a dipole here but I tend to think it probably wouldn't give me all the bands my endfed does.

 

[wbswetnam]

The OP is a newbie and I was trying not to overwhelm him with all of the possible options available. An OCFD is a very simple antenna design and easy to make. The balun itself can be purchased, and from that point all he has to do is connect the appropriate lengths for the legs of the dipole, connect a feed line to the balun, and hoist it up.

 

[WA8ZTZ]

Without knowing the kind of listening and frequencies the OP is interested we are all sort of guessing.
However, all of the suggestions would work better over a range of frequencies than a simple dipole.