40M half wave single wire sloper antenna swr question...Cut or Add ??

[fiddlefaddle99]

I am new to antenna building and catching on quickly. I made a 40M 1/2 wave single wire sloper antenna, wire is cut to 68 feet so I have lots to cut or add if necessary. The actual current antenna length is approx 67 feet and according to my SWR analyzer readings there is some tweaking needed. Out of my radio I have 30 feet of RG8X to a LDG 9:1 unun which feeds the wire and the negative side of the unun I have to ground. I am mostly interested in the 40m & 20M band. To tweak the wire to get a decent reading on both bands should I start cutting or adding wire ? And which band should I work with to get the other to fall into place. I know there any many other variables but from what I have been reading antenna length is were to start. My current readings are below. Thanks in advance

7.100mhz 3.2 SWR
7.150mhz 3.3 SWR
7.250mhz 3.5 SWR
7.300mhz 3.6 SWR
14.100mhz 2.4 SWR
14.150mhz 2.4 SWR
14.250mhz 2.5 SWR
14,300mhz 2.5 SWR

 

[K6GBW]

Well, you are using a half wave length wire with a 9:1 unun. The 9:1 unun is designed for non-resonant wire lengths and meant to be used with a tuner. So, you have two choices, you can change the transformer to a 49:1 meant for the wire length you're using, or you can shorten the wire you have to about 58-59 feet. That length will probably tune up fine with the rigs internal tuner, but depending on how it's deployed it might not and will require an external tuner.

I think you'll find that the 49:1 unun with 66 or so feet of wire will have better performance, but many like the versatility of the 9:1 because it can be used with non-resonant lengths and can be made shorter. If you decide to stick with the 9:1 unun you can use a wire length from one of the cheater charts made by Balun Designs: https://www.balundesigns.com/content/Wire Lengths for 4 and 9-1 ununs.pdf

 

[fiddlefaddle99]

Thanks for the reply, I do have the room for a long wire so if I went to 124.5 feet of wire as per the chart with the 9:1 would that give me better performance across the bands than a 49:1 at 66 feet ? I know either one wont be perfect, just what would be best for overall performance.

Well, you are using a half wave length wire with a 9:1 unun. The 9:1 unun is designed for non-resonant wire lengths and meant to be used with a tuner. So, you have two choices, you can change the transformer to a 49:1 meant for the wire length you're using, or you can shorten the wire you have to about 58-59 feet. That length will probably tune up fine with the rigs internal tuner, but depending on how it's deployed it might not and will require an external tuner.

I think you'll find that the 49:1 unun with 66 or so feet of wire will have better performance, but many like the versatility of the 9:1 because it can be used with non-resonant lengths and can be made shorter. If you decide to stick with the 9:1 unun you can use a wire length from one of the cheater charts made by Balun Designs: https://www.balundesigns.com/content/Wire Lengths for 4 and 9-1 ununs.pdf

 

[jhooten]

If SWR goes up as frequency goes up the wire is too long.
If SWR goes up as frequency goes down the wire is too short.

 

[fiddlefaddle99]

Thank You

If SWR goes up as frequency goes up the wire is too long.
If SWR goes up as frequency goes down the wire is too short.

 

[K6GBW]

It sounds like you are confused about two different types of antennas. There are End Fed Half Waves (EFHW) that uses a resonant length of wire for it's lowest band. An example would be 66 feet of wire, which is a halfwave length for 40 meters. These antennas use a 49:1 transformer because the voltage on the end of the wire is very high (something on the order of 2,450 ohms) or there abouts. Another type of antenna that looks similar but is very different is the Non-Resonant wire antenna that is often called a "Random Wire" antenna. The Non-Resonant wire antenna uses lengths of wire that are not resonant lengths. So instead of 66 feet the wire is shortened or lengthened to be slightly short or long. This antenna usually has a voltage at the end of the wire somewhere around 450 to 600 ohms. This is low enough to use a good tuner to make it work.

When you originally posted you said you were using 68 feet of wire with a 9:1 unun. Thats a resonant length so the Ohms will be too high for the transformer to handle. If you shorten it to a length such as; 44 - 53 - 58 - 73 feet then it will work better. That said, if you already have 66 feet strung up you can change to a 49:1 Unun and make it into an EFHW. The EFHW can be made to with with no tuner or very little tuning with a rigs internal tuner.

So, the best approach would be to tell us which bands you are interested in working? If you only want 40 to 10 meters then you will be better served with the 66' EFHW because it does not require counterpoise wires and has lower noise and better power output. But, if you want 80 meters you can use the 9:1 and trim your current wire to a length like 53 feet and it will work 80-10 meters as long as you use an external tuner. Non-Resonant wire antennas can be very problematic as they tend to create common mode and they can be finicky, not wanting to tune on some bands.

I recommend you do some on-line research about the differences between a EFHW and a Non-Resonant wire antenna before you decided.

 

[prcguy]

What bands are you trying to work? If you are trying to work 40-10 meters then a 66 foot wite with a 49:1 Unun will cover that nicely.

I agree, a resonant end fed half wave with 49:1 will outperform any 9:1 setup and you shouldn’t need a tuner on the resonant bands. The 9:1 types are only good to get the match low enough for the tuner in your radio to take over and are not intended to provide a perfect match. They also use the coax as the other half of the antenna and will usually make the coax hot with RF.

 

[fiddlefaddle99]

Got it, a little more homework for me. Thanks

 

[fiddlefaddle99]

Read up on single wire antenna's and get it 90%....So I am most interested in 40m & 20m, 10m would be nice and if I could get 80m that would be a bonus but not necessary (20m & 40m are priority). I have lots of room to run a single wire either straight or slopped. What would be the recommended way to go ?

 

[prcguy]

Read up on single wire antenna's and get it 90%....So I am most interested in 40m & 20m, 10m would be nice and if I could get 80m that would be a bonus but not necessary (20m & 40m are priority). I have lots of room to run a single wire either straight or slopped. What would be the recommended way to go ?

A half wave end fed for 40m is about 64ft long and with a broad band 49:1 transformer will cover 20, 15 and 10m without a tuner. If you end up hopping for a commercially made version I would recommend MyAntennas. Or you can build a 400w transformer for about $25 including a weatherproof housing, connector and stainless steel hardware.

 

[K6GBW]

Have to agree with prcguy. I've built and used both types and the EFHW is much easier to deal with.

 

[fiddlefaddle99]

Excellent, I will build a EFHW starting at 66ft and cutting back to tweak my antennas SWR, Im assuming I setup the SWR on the 40M band and let the others fall in place ? What exact frequency should I use for cutting to set the SWR ?

 

[K6GBW]

Yes, and the exact frequency really depends on where you like to transmit. Most people probably shoot for 7.150 MHz or right around there. With the EFHW you should be good over the whole band though. You can also touch it up with the rigs internal tuner if it has one.

 

[prcguy]

Have to agree with prcguy. I've built and used both types and the EFHW is much easier to deal with.

I agree with you, you agree with me, people are gonna think we eat lunch together and discuss RR antenna topics if this keeps up.

On trimming a EFHW to resonance, just remember all the bands will be harmonically related, so if you trim 40m for 7.150 then 20m will resonate at 14.300, 15m at 21.450 and 10m at 28.6. You can adjust slightly to favor a specific band and frequency and fortunately the antenna will be broad enough to cover most of each band.

 

[smason]

people are gonna think we eat lunch together and discuss RR antenna topics if this keeps up.

Not that there's anything wrong with that....

 

[K6GBW]

We be the L.A. Radio Mafia!

 

[fiddlefaddle99]

Now running a 49:1 unun with approx 64.5 foot wire antenna at 7.150 I have an SWR 1.35, at 7.25 swr 1.48 and at 7.35 swr 1.70. At 14.100 swr 1.26, at 14.200 swr 1.27, at 14.300 swr 1.36. To tweet and get lower should I cut or add ?? Thanks

A half wave end fed for 40m is about 64ft long and with a broad band 49:1 transformer will cover 20, 15 and 10m without a tuner. If you end up hopping for a commercially made version I would recommend MyAntennas. Or you can build a 400w transformer for about $25 including a weatherproof housing, connector and stainless steel hardware.

 

[prcguy]

Now running a 49:1 unun with approx 64.5 foot wire antenna at 7.150 I have an SWR 1.35, at 7.25 swr 1.48 and at 7.35 swr 1.70. At 14.100 swr 1.26, at 14.200 swr 1.27, at 14.300 swr 1.36. To tweet and get lower should I cut or add ?? Thanks

It sounds maybe a little long to me but if it were mine I would leave as is. I don't do CW and favor the upper phone portion of the bands and your SWR looks totally acceptable from 7.15 through 7.3 and also the entire CW and phone sections of 20m. If you were to shorten it about 6" it might center the sweet spot more in the phone areas but why bother.

Have you tested 10m? I would expect that to come in around 28.2 where they usually run about 28.5 or so. Do you have the typical coil of wire about 6ft out from the transformer? Its something like 6 turns around a 1" form and I have the exact specs somewhere. I'm not sure what band it targets but its used on some commercial 40 and 80m versions and possibly affects 10m.

 

[fiddlefaddle99]

Crazy question...Will a wire antenna SWR change slightly at different times of day or due temperature/weather ? My readings are lower this morning.

 

[K3DMY]

I am new to antenna building and catching on quickly. I made a 40M 1/2 wave single wire sloper antenna, wire is cut to 68 feet so I have lots to cut or add if necessary. The actual current antenna length is approx 67 feet and according to my SWR analyzer readings there is some tweaking needed. Out of my radio I have 30 feet of RG8X to a LDG 9:1 unun which feeds the wire and the negative side of the unun I have to ground. I am mostly interested in the 40m & 20M band. To tweak the wire to get a decent reading on both bands should I start cutting or adding wire ? And which band should I work with to get the other to fall into place. I know there any many other variables but from what I have been reading antenna length is were to start. My current readings are below. Thanks in advance

7.100mhz 3.2 SWR
7.150mhz 3.3 SWR
7.250mhz 3.5 SWR
7.300mhz 3.6 SWR
14.100mhz 2.4 SWR
14.150mhz 2.4 SWR
14.250mhz 2.5 SWR
14,300mhz 2.5 SWR

According to your VSWR readings, your wire is too long. I always reduce the wire length 3" to 4 " increments and fold it back on itself until you reach the desired resonant point then cut off the excess wire. Make your final wire wraps at your insulators smooth (no strands sticking outward) as the burrs can create corona noise, every little bit helps. You may also want to consider adding a CURRENT BALUN at the feedpoint of the UNUN to eliminate RF currents on the coax, they're easy to make You will need to connect an earth ground to the low side (shield or connector flange of the UNUN) of the coax connector. The CURRENT BALUN not eliminates RF on the outer jacket of the coaxial feed line, It will also reduce noise in general from reaching the receiver. I have found the addition of CURRENT BALUN improves my receiving noise floor on my ICOM 605.

Crazy question...Will a wire antenna SWR change slightly at different times of day or due temperature/weather ? My readings are lower this morning.

Yes, the change is most likely due to changes in soil conductivity, wet seasons to dry seasons. A counterpoise wire laid out under your antenna should help.