Horizontal Dipole vs Inverted V Dipole

[Delta 26]

Recently I was experimenting with dipole antennas, When I have it in the Horizontal position I can get the SWR to 1 on Channel 1 and 1.3 on Channel 40. I am using 50ft of RG58 mini coax cable. It is 6.5ft off the ground. As a note it picked up the Skip on March 01, 2017 great and I could hear communications from Southern California to Rhode Island from Alabama to Washington and one guy calling from Jamaica. I tried to call out but I didn't get any confirmed contacts and I couldn't talk locally. I have a little Italian helper also.

When trying to rig it up as a inverted V I pulled it up into the air at 36ft. using the same cable and hooked to my Mobil unit. The SWR this time was just under 3 on both channels.

1. Why does the SWR change when rigged up as a inverted V?

2. Does the pole length need to be adjusted for each configuration?

3. Does it need to be earthed?

[The DB]

When I have it in the Horizontal position I can get the SWR to 1 on Channel 1 and 1.3 on Channel 40. I am using 50ft of RG58 mini coax cable.

A horizontal dipole antenna should not tune to that low an SWR on any channel, being closer to 1.5 at its lowest point. The reason it appears to be as low as it is is the coax you are using, and with an antenna that is tuned to 1.5:1 SWR will actually loose over 20% of both the transmitted and received signals, and that is assuming it is the more expensive Belkin brand RG-58 and not some of the real crap that is available. In addition to the loss of signal, these feed line losses make SWR appear to be lower than they are. I once did a test on some of the real cheap RG-58, and 100 feet of it it brought a 5:1 SWR at the antenna end down below 2:1 SWR at the radio end.

1. Why does the SWR change when rigged up as a inverted V?

The elements are no longer in line with each other. This is enough to change the antennas feed point impedance, and by extension the antenna's SWR.

2. Does the pole length need to be adjusted for each configuration?

Yes, the antenna needs to be re tuned.

3. Does it need to be earthed?

Antenna's don't need to be earthed to function, that is more for lightening safety than anything.


The DB

[Delta 26]

Got it.

[Mtn Lynx]

yesterday while skip was rolling I switched antennas from my a99 to my horizontal dipole which is appx 20 feet off the ground beside my house. Didn't think I would hear anything. But to my surprise it didn't make too much of a difference. my a99 is about 30 ft high at the base of the antenna. Hawaii was coming in just as loud on my dipole.

[Delta 26]

@ "The DB" I have been checking other threads and looking at coax. Ive seen comments on RG 8, RG 213, and the LMR products. I would like to buy on set of long coax if possible. I have a really tall tree id like to transmit out of. Just guessing it is 50-75 ft high. So which one would be a good coax to use Id say 100 ft run is the maximum I would ever want to run. I would run it up the tree experiment and then try something else so it needs to be durable.

The price swings a big higher as you get better I just don't want to waste the $.

[Mtn Lynx]

I run rg8x it does the job, don't think you need to get the pricey one

[MDYoungblood]

The difference between a truly horizontal dipole and a inverted V is their impedance, I believe DB stated that, on an inverted V the closer the ends of the dipole come the closer to 50ohms it becomes, both will still be horizontal polarity, also the closer they come the antenna becomes more unidirectional.
I think there are quite a few posts on coax here on the forum, a search will show them. My rule of thumb is the smaller coax, RG58, RG8X, is for short runs (20ft or less, 50ft max) and jumpers between the equipment, RG8, RG213 ,or equivalent are good to 50 to 75ft, and longer runs I wouldn't use any other than LMR or equivalent. If you are or plan to run any kind of power (more than just the radio), the large quality coax is a must,These statements are just my opinion.

3's

Greg

[The DB]

@ "The DB" I have been checking other threads and looking at coax. Ive seen comments on RG 8, RG 213, and the LMR products. I would like to buy on set of long coax if possible. I have a really tall tree id like to transmit out of. Just guessing it is 50-75 ft high. So which one would be a good coax to use Id say 100 ft run is the maximum I would ever want to run. I would run it up the tree experiment and then try something else so it needs to be durable.

The price swings a big higher as you get better I just don't want to waste the $.

To give an idea of the efficiency of the different coax cables, the number of feet it takes to loose 10% of your transmitted power in the coax when you have an SWR of 1.5:1 at the antenna end you get the following lengths. Note, these are using Belkin brand cables, brands of lesser quality will obviously be worse than the numbers presented here.

RG-58C, 15 feet.
RG58A, 20 feet.
RG-58, 21 feet.
RG-8x. 27 feet.
LMR-240, 33 feet.
RG-213, 41 feet.
RG-8, 45 feet.
LMR-400, 67 feet.

And while I am playing with this calculator http://www.qsl.net/co8tw/Coax_Calculator.htm, a few more things for fun...

300 ohm twin lead, 77 feet.
Andrew Heliax LDF-450A, 124 feet.
450 ohm window line, 287 feet.
600 ohm ladder line, 418 feet.

This should give an idea of what to expect from the various cables available.


The DB

[Delta 26]

Thanks for the info. I appreciate it.