fan harmonics

[rjvalenta]

i'm new to HF... and as i posted in a different thread i'm considering an MFJ Octopus, which is effectively a fan dipole.

i have to choose 4 dipoles made of hamsticks to put in this - which will connect to my tuner.

i was watching one of Dave Casler's videos (the man has taught me so much), and he made a comment about 15m being a harmonic of 40m...

i started to think about that... 7mhz at 40... 21mhz at 15...

wait... 7Mhz for 40m, 14Mhz for 20m, 21Mhz for 15m, 28Mhz for 10m... aren't they all harmonics of each other?

no wait, 5Mhz for 60m, 10Mhz for 30m

and then 24Mhz for 12m, 50Mhz for 6m...

with a tuner - a 75m hamstick dipole would be able to get on 80/75... then with a 20m hamstick dipole i would also be able to work 40m, 15m, and 10m... then with a 30m hamstick dipole i would also 60m, and finally a 17m dipole would also get me on 6m?

so the perfect mix (with a tuner) to get the most band would (at least in theory) be 75/30/20/17

am i understanding harmonics properly?

 

[AK9R]

The original amateur radio HF bands are kinda, sorta harmonically related. The WARC bands (30m, 17m, 12m) not so much.

3.5-4.0 MHz is 2nd harmonic of 1.8-2.0 MHz.
7.0-7.3 MHz is 2nd harmonic of 3.5-4.0 MHz.
14.0-14.35 MHz is 2nd harmonic of 7.0-7.3 MHz.
21.0-21.45 MHz is 3rd harmonic of 7.0-7.3 MHz.
28.0-29.7 MHz is 2nd harmonic of 14.0-14.35 MHz.

The relationships are not exact, but close enough for building dipole antennas back in the days before everyone had an SWR meter or antenna analyzer or VNA.

 

[rjvalenta]

ok - but i guess my question is: can you use an antenna resonant on one band for it's harmonic bands?

like i hear about a resonant antenna, and then a 1/2 wave or a 1/4 wave antenna... so... a 20m resonant dipole would be a 1/2 wave dipole for 40m and a 1/4 wave dipole for 80m... and... double wave for 10m?

does it work like that?

and if it doesn't work like that as just the antenna, does it with a tuner?

 

[AK9R]

A dipole for 20m would be about 33 feet long and would be fed at the center. 33 feet is half of the wavelength on 20m. It might "work" on 40m, but most of the RF energy will be used up in the antenna matching unit, aka "tuner".

A 1/4 wave antenna can be thought of as a dipole (1/2 wave antenna) with half of the antenna in the counterpoise.

 

[rjvalenta]

does that work in both directions? meaning... would a 40m dipole transmitting a 20m signal through a tuner suffer similar losses or are they less with a longer (lower frequency) starting resonance?

 

[AK9R]

A 40m dipole used on 20m would be a full-wave antenna. Full-wave antennas are usually avoided because positive- and negative-swinging charges in the antenna tend to cancel each other out.

I've been searching for some basic antenna theory articles on the Internet and I think I found something that might be useful to you. Start with this page: Antenna Theory Tutorial Then, look at the pages for Fundamentals, Basic Parameters, Half-Wave Dipole, and Full-Wave Dipole. Study all of the articles if you have the time.

 

[rjvalenta]

now i'm consumed with the idea of the folded dipole i'm reading about in this tutorial... this would all be easier if i lived on a farm and had space and multiple towers for all the things i'd like to try.

 

[AK9R]

The lot that my house sits on is 90 feet wide. I have a dipole for 75m (approximately 133 feet long) stretched across my lot. Where the wires for the two elements hit the lot lines, I turned the wires 90 degrees and ran them along the top of a wooden privacy fence. The antenna works. It's not the best 75m dipole, but it works.

There's no law that dipole wires have to run in a straight line. Folded dipoles have been used for years.

 

[krokus]

... this would all be easier if i lived on a farm and had space and multiple towers for all the things i'd like to try.

Welcome to the world of HF antennas. Most of us would like to have more room, for a better antenna farm.

 

[N6SPP]

The lot that my house sits on is 90 feet wide. I have a dipole for 75m (approximately 133 feet long) stretched across my lot. Where the wires for the two elements hit the lot lines, I turned the wires 90 degrees and ran them along the top of a wooden privacy fence. The antenna works. It's not the best 75m dipole, but it works.

There's no law that dipole wires have to run in a straight line. Folded dipoles have been used for years.

I echo what you say about the physical angles of the wire legs.. Same on my lot. One of my antennas is an old Carolina Windom (OCFD 6-80m,w/ a vertical coax radiator section).. The feed point is @ ~ 25ft up in the corner of the fence. The shorter 45ft leg angles down to the 6ft fence line, while the 90ft leg is at a 90degree angle (to the 45ft leg) and runs across the lot and above roof. Additionally, the 90ft leg was too long and so I bent about 15ft of it which runs at another angle..hi.. To new hams with wire antennas- fit whatever (@Resonance/near resonance) wire you can inside your property lines and make slight angle bends if necessary. 73,n6spp-cm98

 

[N6SPP]

i'm new to HF... and as i posted in a different thread i'm considering an MFJ Octopus, which is effectively a fan dipole.

i have to choose 4 dipoles made of hamsticks to put in this - which will connect to my tuner.

i was watching one of Dave Casler's videos (the man has taught me so much), and he made a comment about 15m being a harmonic of 40m...

i started to think about that... 7mhz at 40... 21mhz at 15...

wait... 7Mhz for 40m, 14Mhz for 20m, 21Mhz for 15m, 28Mhz for 10m... aren't they all harmonics of each other?

no wait, 5Mhz for 60m, 10Mhz for 30m

and then 24Mhz for 12m, 50Mhz for 6m...

with a tuner - a 75m hamstick dipole would be able to get on 80/75... then with a 20m hamstick dipole i would also be able to work 40m, 15m, and 10m... then with a 30m hamstick dipole i would also 60m, and finally a 17m dipole would also get me on 6m?

so the perfect mix (with a tuner) to get the most band would (at least in theory) be 75/30/20/17

am i understanding harmonics properly?

Hello RJ- Ok on MFJ's multi 3/8 thread 'octopus' single feed system.. Here is a side note+ tip for those using a pair of 'Hamsticks" as a dipole (using a ~ $18 dual 3/8in thread dipole feed unit w/ SO-239)- I've used the original "Hamsticks" from Valor/Pro-AM and also Hustler resonator 1/4 wave mobile antennas in a dipole fashion on a few hf bands. When using a pair of 40m Sticks close to the ground, try using them in a vertical dipole configuration. Ensure the lower counterpoise element is at least a foot off of the ground. At 7MHz, you will experience a decent take-off angle and will not have to worry about "getting a (horizontal) 40mtr dipole a half wave up, above the ground" (for a few dB of gain and/or interaction from being too close to the avg asl).. Try to run/route the coax as close to perpendicular from the feedpoint as possible too, to maintain a ~40-150 ohm impedance (something an ITU or outboard tuner can handle). When using my Budipole in the field on 40 + 60m , I config it in the same manner.. 6-20m is a little different depending on available mounting height etc.. 73,n6spp-cm98