OCF swr issue

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jazzboypro

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Hello all,

A few weeks ago i installed an EFHW 4010 that i bought from myantennas.com. The antenna worked well but of course i could not use it on 80 meter. Last week i ordered the OCF-8010 from myantennas.com. Yesterday i removed the 4010 and i installed the 8010 so i'm using the same coax (LMR400) the same RF choke (also bought from myantennas.com) and the same polyphaser.

Yesterday evening i started testing the 8010 and it did not went well.

SWR is thru the roof on 15-20-80 meter and the internal tuner won't match it. 5 watts is the maximum power i can use on those bands before SWR rises sharply, the other bands are ok.

The OCF ratio is 19%/81%. The transformer is on a mast at about 25 feet (same place as the 4010 that i removed). The shorter leg is in a straight line and runs from the transformer to a tree in front of the house. The first 50 feet of the longer leg runs in a straight line from the transformer to a tree in the backyard (same path as the 4010 i removed)

At the tree the wire makes a 90 degree turn and the remaining 56 feet is in a straight line and is attached to a mast at the other extremity of the house. Un fortunately about half of the last 56 feet runs parallel to the power utility service drop but about 7 feet away from it in the horizontal plane and about the same hight on the vertical plane. The second half of the las 56 feet is over the roof of the house maybe a feet or so above the roof in a certain portion (because of the angle of the roof).

Before i take the 8010 down and put back the 4010 do any of you have suggestions on something i might try to make the 8010 work better ?

Many thanks

73 de VA2FCS
 

prcguy

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All the bands on these antennas are harmonically related so it might be good to map out all the bands and record where the best match is. For example if the SWR dips at 7.15MHz then it should also dip at 14.3, 21.45 and 28.6MHz. 80m will actually resonate low like 3.57MHz and SWR will rise through the 75m phone band. This is normal because 80m is not harmonically related to any other amateur bands. If your new antenna dips in SWR around the frequencies I mentioned its probably ok.

There is not much to go wrong with these antennas as the transformer is very broad band and the coil in the wire close to the transformer is to help smooth out one of the bands, 10m I think. You can test the transformer by removing the wire and placing a non inductive resistor around 2.5k ohms across the output stud and ground. That should show a good match from at least 3 to 30MHz and substituting resistors between 2k and 3k ohms will find the sweet spot. Or you can connect the output stud of your 40m version to the 80m version, connected the ground side of the SO-239s together, put a 50 ohm load on one transformer and an antenna analyzer on the other and it should show a good match at least through 40-10m.

There is a mod for 80m to slide it up to the 3.8-4MHz range dipping around 3.9MHz without affecting any other bands. MyAntennas also makes a version with the mod. I can post the mod if needed.
 

jazzboypro

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All the bands on these antennas are harmonically related so it might be good to map out all the bands and record where the best match is. For example if the SWR dips at 7.15MHz then it should also dip at 14.3, 21.45 and 28.6MHz. 80m will actually resonate low like 3.57MHz and SWR will rise through the 75m phone band. This is normal because 80m is not harmonically related to any other amateur bands. If your new antenna dips in SWR around the frequencies I mentioned its probably ok.

There is not much to go wrong with these antennas as the transformer is very broad band and the coil in the wire close to the transformer is to help smooth out one of the bands, 10m I think. You can test the transformer by removing the wire and placing a non inductive resistor around 2.5k ohms across the output stud and ground. That should show a good match from at least 3 to 30MHz and substituting resistors between 2k and 3k ohms will find the sweet spot. Or you can connect the output stud of your 40m version to the 80m version, connected the ground side of the SO-239s together, put a 50 ohm load on one transformer and an antenna analyzer on the other and it should show a good match at least through 40-10m.

There is a mod for 80m to slide it up to the 3.8-4MHz range dipping around 3.9MHz without affecting any other bands. MyAntennas also makes a version with the mod. I can post the mod if needed.
Thanks for the info. I have not tested the antenna to find out the best match like you said. I have tested the antenna on FT8 only and this is where i would like the antenna to work best.
 

K6GBW

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Question, did you secure the coax to the mast? Many people using OCFD antennas for the first time do this and it will cause problems. Best to let the coax hang free and not be against the mast.
 

tweiss3

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The MyAntennas do not cover the entirety of 80m. It either covers the voice portion OR the digital portion, but there isn't enough bandwidth on 80 to cover both.
 

prcguy

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The MyAntennas do not cover the entirety of 80m. It either covers the voice portion OR the digital portion, but there isn't enough bandwidth on 80 to cover both.
For a stock 80m EFHW to cover the 3.8 to 4.0MHz phone band without affecting any other band, find the exact center of the wire, cut in half, install an insulator then bridge the insulator with a 250pf doorknob or other high voltage cap. You can also install a jumper wire to revert back to the CW portion of the band. I've done this on several MyAntennas EFHWs and also the OCFD but that takes a different value cap. The value of the cap in this picture is wrong and was an experiment. With lugs on the wires you can swap around other caps or bolt the two wires back together for stock operation.

1692200665460.jpeg
 

jazzboypro

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This antenna is getting weirder to me. The day after my original post i modified the lay out of the longer leg and everything was fine except on 17 meter. I bought a AA-55 Zoom and found out that swr on 17 meter is 7. On the other bands swr is acceptable and the internal antenna tuner can deal with it. I made several contacts on most bands. the las 2 days i did not do anything as i was out with COVID. Today i wanted to make some contacts on FT8 ON 20 meter and i noticed the swr was high again. I check the antenna again with the analyzer and found out that SWR is high on every band (7 to 20 depending on the band).

So far i suspect it is a water/humidity issue since we had a bit of rain last night and this morning. On this particular antenna both ends of the wire are fitted with a plastic tip and i did not provide anymore weather proofing.

The coax is attached underneath the transformer and i put 3M Tenflex 2135 and 3M Super33+ electrical tape on the connection. The transformer itself did not look like it needed weather proofing. Apart from a small portion of the longer that's in a tree, the rest of the antenna is in the clear so it's not soaking in water or touching wet/damp surface.

If any of you has that particular antenna, should i weather proofing on the antenna ends and on the transformer ?

@K6GBW At the moment the coax is not attached to the mast
 

jazzboypro

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So...i have changed the layout of the longer leg again and i minimized to the maximum the part that runs thru the tree. Unfortunately it did not solved anything. I took the following measurements after modifying the antenna path.

6 meter (not officially supported): SWR=3.8 Z=17.3 Ohm
10 meter: SWR=5.9 Z=55.7 Ohm
12 meter: SWR=9.2 Z=25.4 Ohm
15 meter: SWR=9.9 Z=212.9 Ohm
17 meter (not officially supported): SWR=13 Z=20.7 Ohm
20 meter: SWR=12 Z=20.9 Ohm
30 meter: SWR=14 Z=161.9 Ohm
40 meter: SWR=18 Z=32.1 Ohm
80 meter: SWR=26 Z=28.7 Ohm
160 meter (not officially supported) SWR=1.28 Z=50 Ohm

It looks like the tree is not the issue. If it had never worked i would have think that the antenna layout just won't worked for some reason but it worked on 10-12-30-40 on the first layout. After the second layout i got the other bands to work too except 17 meter and as of today it stopped working on every band. Like i said we had some rain so tomorrow i will open the transformer to see if water got in it. Any other idea of what the problem might be ?
 

KK2DOG

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I have the 124' version mounted at about 25' in the air and it plays well on all bands 10-80 regardless of whether I'm on SSB or FT4/FT8. I do have a ground wire connected to the grounding stud on the transformer box and that goes to a 4' ground rod hammered into the ground. I can even run an amplifier without any issues and I use the LDG 600 auto-tuner as well. My coax is secured to a metal mast up on the roof with nylon zip-ties and my line isolator/choke is in the shack. I've had zero issues for many years.
 

KK2DOG

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Disregard my earlier comment. Somehow I missed the fact that you were talking about an OCF dipole and not a 10-80 EFHW.
 

G7RUX

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SWR is thru the roof on 15-20-80 meter and the internal tuner won't match it. 5 watts is the maximum power i can use on those bands before SWR rises sharply, the other bands are ok.
This part of your post intrigues me…the return loss *shouldn’t* depend on the input power.
What are you using to measure the VSWR? Internal SWR bridges in transceivers are notoriously unreliable in lots of circumstances.

Are you certain that nothing is breaking down at the higher power levels? I have a shocks portable antenna that does this with a bit much power and it gets worse as the feedpoint warms up with use.
 

popnokick

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Likely culprit is coaxial cable connectors. How many sections of LMR400 do you have (rig>MyAntennas choke>polyphaser>MyAntennas OCF transformer)? When you added the additional choke / sections did you crimp / solder the coax connectors yourself? What is the part that is "fitted with a plastic tip"? Have you detached the coax from the transformer and performed the check suggested by prcguy? (50 ohm termination on one end, your RigExpert AA-55 on the other.) With the meter inline and disconnected from the antenna, have you wiggled the coax in the connector at every junction to see if the reading changes?
 

jazzboypro

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This part of your post intrigues me…the return loss *shouldn’t* depend on the input power.
What are you using to measure the VSWR? Internal SWR bridges in transceivers are notoriously unreliable in lots of circumstances.

Are you certain that nothing is breaking down at the higher power levels? I have a shocks portable antenna that does this with a bit much power and it gets worse as the feedpoint warms up with use.
I also thought that the SWR would remain constant no matter the power but it is not the case. I’m not sure what you mean by something breaking down at higher power. The measurements were taken using a RigExpert SS-55 Zoom.
Likely culprit is coaxial cable connectors. How many sections of LMR400 do you have (rig>MyAntennas choke>polyphaser>MyAntennas OCF transformer)? When you added the additional choke / sections did you crimp / solder the coax connectors yourself? What is the part that is "fitted with a plastic tip"? Have you detached the coax from the transformer and performed the check suggested by prcguy? (50 ohm termination on one end, your RigExpert AA-55 on the other.) With the meter inline and disconnected from the antenna, have you wiggled the coax in the connector at every junction to see if the reading changes?
I have 3 sections of LM400 (Cables were bought pre-made with connectors already installed. The cables were tested prior to installation and until last week the whole feedline/choke/polyphase assembly was feeding an EFHW 4010 without issues)

First section: From antenna transformer to rf choke, PL-259 at both ends (The choke is from myantennas.com)

Second section; From rf choke to polyphaser, PL-259 on the choke side and N connector on the polyphaser side. The polyphaser is installed outside at the coax entry point into the house and is grounded to the house ground. The polyphaser is enclosed in a plastic electrical box attached to the exterior wall of the house..

Third section: From the polyphaser to the radio, N connector on the polyphaser side and PL-259 on the radio side.

All connections (except at the radio end) were weather proofed using 3M Tenflex and 3M 33+ electrical tape.

The parts fitted with a plastic tip are the far end of each leg of the antenna.

Keep in mind that there is no homebrewed components in this antenna sytem. The antenna and choke were bought from myantennas.com who seems to have a good reputation. The polyphaser was bought from Polyphaser and the coax were bought with connectors installed from the antenna farm. Again, until last week the whole feedlline assembly was feeding an EFHW 4010 (also bought from my antennas.com) for 2 months without any issues.

Today I will remove the antenna to see if water got into the transformer and check the connection of the coax at the transformer. The other tests will have to wait because a don’t have anything to terminate the coax at one end and put the other in the Analyser. As far as I can tell the only thing that happened between working and not working is the rain.
 

jazzboypro

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A quick update....

The value i posted a few posts up were taken yesterday at 20:00. It also rained last night. When i got up this morning at 8:00 i measured the SWR again. It was a bit better but still very high on every band. I took my coffee, had breakfast as i wanted the roof to dry before i got up. At 10:30 i was preparing to go up but i decided to measure SWR again so i have fresh values before inspecting the antenna. To my surprise SWR was much better on every band even excellent on some. I'm going to inspect the antenna now. I really don't understand what's happening and what makes the problem intermittent.

BandSWRRLZ
101.4115.443
123.15.72102.3
154.93.5998.2
177.22.4411.8
204.14.1837.6
303.25.4440.8
401.6211.756
804.23.36111.3
 

popnokick

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If there has been water ingress into any part of the system physical inspection alone may not show where. You may have to disassemble and test each section of cable / connectors separately using the RigExpert and a 50 ohm terminator. Same is true with the MyAntennas transformer and connecting the RigExpert to it. However, I believe the MyAntennas site has an FAQ regarding how to test their EFHW and it is not as direct as simply connecting an analyzer looking for low SWR.
 

jazzboypro

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If there has been water ingress into any part of the system physical inspection alone may not show where. You may have to disassemble and test each section of cable / connectors separately using the RigExpert and a 50 ohm terminator. Same is true with the MyAntennas transformer and connecting the RigExpert to it. However, I believe the MyAntennas site has an FAQ regarding how to test their EFHW and it is not as direct as simply connecting an analyzer looking for low SWR.

I will look at their website but the antenna i'm troubleshooting is an OCF not a EFHW
 

popnokick

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Sorry... forgot you replaced EFHW with OCFD. Look for instructions regarding attaching an analyzer directly to the OCFD transformer. I've never done it directly to mine so I'm not sure if different considerations apply when you connect to transformer directly.
 

popnokick

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The MyAntennas transformer / balun is probably fine. But here's another take on how to test it without the antenna elements connected to it. Scroll down to the section labeled "Testing the Balun". Wherever you see references to an MFJ or other analyzer, substitute your RigExpert. How to Buuild a 4:1 Current Balun - by KB1LQC
 

jazzboypro

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After opening the transformer a can say with a high degree of certitude that no water got in there. Unless you submerge it in water there is no way water can get in. Also i noticed there are holes in the bottom probably for air circulation and to avoid moisture bild-up inside the transformer. This thing is well built for sure.
 
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