Antenna analyzer and radio don't agree

[jazzboypro]

Hello all,

Some of you might remember a thread i posted a few weeks ago about the myantenna 8010 OCF. Still struggling with it on 80 meter. I tried a new layout of the longer leg today. It's a bit better but not much.

On 80 meter the SWR is acceptable from 3708 to 3838. I am particularly interested in two frequencies because there are local nets daily on one frequency and once a week on the other frequency. The frequencies are:

3780 and 3775

According to the RigExpert AA-ZOOM 55 the SWR is 1.7 on both frequencies, i kind of thought it would be even better when the radio's internal tuner kicks in.
When transmitting on any of the 2 frequencies at 100W the radio's tuner kicks in as soon as i push the PTT. The radio's meter indicates a SWR around 2.5 and about 40 watts out.

I checked again the antenna with the analyzer and it still shows a SWR of 1.7 on both frequencies. Any ideas ?

Many thanks
73 de VA2FCS

 

[prcguy]

Is your antenna the 75m version or the 80m version? The 80m version is typical and resonates around 3.55MHz and gets worse as you go up in frequency. The 75m version has a circuit board with capacitor right in the middle of the antenna and that shifts the 80m resonant point to about 3.9MHz with a great match over 3.8 to 4.0MHz perfect for 75m phone.

Otherwise in a perfect world and with your radio or antenna analyzer connected to the exact same point in the feedline they should read the same or very close. If you have anything different between the measurements like an extra jumper or it goes through some other device, that will give you different readings.

 

[jwt873]

What radio?

If you turn the internal tuner off or disable it, What does the radio's SWR meter show? Is it the same or close to the RigExpert?

The 8010 is a multi band antenna.. Do you see the same thing happening on the higher frequencies? Is the internal tuner effective on 20, 15 and 10 meters?

Just a wild guess... The OCF dipole isn't balanced like a regular dipole. There could be some common mode currents on the coax that are confusing your tuner.

 

[jazzboypro]

What radio?

If you turn the internal tuner off or disable it, What does the radio's SWR meter show? Is it the same or close to the RigExpert?

The 8010 is a multi band antenna.. Do you see the same thing happening on the higher frequencies? Is the internal tuner effective on 20, 15 and 10 meters?

Just a wild guess... The OCF dipole isn't balanced like a regular dipole. There could be some common mode currents on the coax that are confusing your tuner.

The radio is a 7610. On 80 the SWR is a bit lower (2) without the tuner and it seems to be around 50 watts out (radio set at 100w). The other bands are ok with the tuner and the radio outputs around 90 watts when set at 100W. There is an RF choke on the feedline (same brand as the antenna)

 

[jazzboypro]

Is your antenna the 75m version or the 80m version? The 80m version is typical and resonates around 3.55MHz and gets worse as you go up in frequency. The 75m version has a circuit board with capacitor right in the middle of the antenna and that shifts the 80m resonant point to about 3.9MHz with a great match over 3.8 to 4.0MHz perfect for 75m phone.

Otherwise in a perfect world and with your radio or antenna analyzer connected to the exact same point in the feedline they should read the same or very close. If you have anything different between the measurements like an extra jumper or it goes through some other device, that will give you different readings.

I have the only OCF available on their website and it's 80 meter. The 75 or 80 meter is only available for their EFHW. The radio or the analyzer are connected at the radio end of the feedline without any other equipment/jumper in the way

 

[jazzboypro]

Here is an example, i did this just prior to posting this.

This what i measured on 3810



This is what i see on the radio at that same frequency


Not easy to take this picture. As you can see the radio is set to 100W. While TX the power peaked at around 40W and the SWR went a bit above 2.5 but is above 2 during most of the transmission.

I know the antenna is ok, about to weeks ago i installed my antenna to an other amateur's house (he has an OFC 8010 but homemade) the antenna worked fine on all band (but could not cover the entire 80 meter band with low SWR but that's to be expected)

He used the antenna for 2 days without issues (i must admit that he has more room than me to install the antenna and it was in a straight line for a longer portion of what i can provide at my place)

In the mean time i put back my EFHW 4010 with the same feedline and choke and had no problems. When i reinstalled the the OCF 8010 the same issues came back. Won't work on 17 meter and very limited use if at all on 80.

 

[prcguy]

I have the only OCF available on their website and it's 80 meter. The 75 or 80 meter is only available for their EFHW. The radio or the analyzer are connected at the radio end of the feedline without any other equipment/jumper in the way

Aah, then the VSWR in the roughly 3.7 to 4.0MHz range will be high running maybe 2.5:1 at 3.7MHz and probably 4:1 at 4MHz. I have the 3kW rated 80m MyAntennas version here and did the capacitor mod and I 3.8 to 4.0MHz with no tuner, great match. I will look up the mod which is common knowledge and also recommended by Danny at MyAntennas. It only affects 80m and all other bands are unaffected.

 

[prcguy]

Here is what my Icom 7610 shows at 3.810, 3.900 and 3.998MHz on my modified 80m OCFD, very good match with no tuner.

 

[jazzboypro]

@ 3.7MHz SWR is 5.1 it goes down to 1.57 until a reach 3.86MHz from there the SWR rises to reach 6.3 at 4.0

 

[prcguy]

I found the mod for an 80m OCFD, measure the exact center of the antenna and cut the wire, place a 150pf HV capacitor in series. This is how I did mine with an insulator in the center and bridge it with the HV capacitor. Never mind the value of the cap in the picture, it should be 150pf for your OCFD or 250pf for an EFHW.




Here is a suitable capacitor for a fair price. 150pf 5kv Ceramic Doorknob | eBay

 

[jazzboypro]

I found the mod for an 80m OCFD, measure the exact center of the antenna and cut the wire, place a 150pf HV capacitor in series. This is how I did mine with an insulator in the center and bridge it with the HV capacitor. Never mind the value of the cap in the picture, it should be 150pf for your OCFD or 250pf for an EFHW.


View attachment 148634

Here is a suitable capacitor for a fair price. 150pf 5kv Ceramic Doorknob | eBay

Thanks for the info. At this point i might as well try it !!!

 

[prcguy]

@ 3.7MHz SWR is 5.1 it goes down to 1.57 until a reach 3.86MHz from there the SWR rises to reach 6.3 at 4.0

That sounds a little high but with a stock 80m version you will have a good match in the CW/data end of the band then you will need a tuner in the phone portion. Do the mod and enjoy a good match where you operate. Since 150pf favors roughly 3.9MHz with a great match over 3.8 to 4.0Mhz you could use maybe 160-170pf to target a perfect match at 3.775-3.780.

 

[jazzboypro]

Here is what my Icom 7610 shows at 3.810, 3.900 and 3.998MHz on my modified 80m OCFD, very good match with no tuner.

View attachment 148631
View attachment 148632
View attachment 148633

I wish i had the same !!!

 

[jazzboypro]

That sounds a little high but with a stock 80m version you will have a good match in the CW/data end of the band then you will need a tuner in the phone portion. Do the mod and enjoy a good match where you operate. Since 150pf favors roughly 3.9MHz with a great match over 3.8 to 4.0Mhz you could use maybe 160-170pf to target a perfect match at 3.775-3.780.

Lol SWR is even worse in the CW portion, it's in the double digits. I will try the capacitor mod so i can say i tried it but the values i get are far away from what you are describing for the antenna without the mod. I won't hold my breath lol. Worse case i'll forget 80 and put back my EFHW 4010.

 

[jazzboypro]

That sounds a little high but with a stock 80m version you will have a good match in the CW/data end of the band then you will need a tuner in the phone portion. Do the mod and enjoy a good match where you operate. Since 150pf favors roughly 3.9MHz with a great match over 3.8 to 4.0Mhz you could use maybe 160-170pf to target a perfect match at 3.775-3.780.

The guy on e-bay says the capacitor "looks" good and that it had not been tested. I already have enough problems with getting the antenna working so i don't really want to throw in parts of unknown quality in the mix. I found this while browsing the internet, would it be good ?

So far i have not found anything in the 160-170pf range. Do you know of a place where i could buy them ?

Thanks

 

[jwt873]

How are you measuring SWR with your rig? In the image you attached, it shows you were in LSB mode when you were transmitting. There is no carrier on SSB. The output of the radio depends on how loud you speak and how the mic gain is set. Were you whistling into the mic to get a reading on the power meter?

If you look at the images prcguy added, you'll see he was using FM mode. This is a much better way to do it since when you squeeze the mic, you're putting out a full 100W carrier with no need to provide any audio.

 

[AK9R]

Not easy to take this picture.

Here's an IC-7610 tip that makes capturing the display a piece of cake:
1. Insert an SD card into the SD card slot on the front of the radio.
1a. Format the SD card in the radio.
2. Go to Menu > Set > Function > Screen Capture [POWER] Switch (on page 6) and make sure it's On.
3. When you want to capture the display, just tap the POWER switch. The radio will write the current display to the SD card as a .png file.
4. You can take the card out of the radio (go to Menu > Set > SD Card > Unmount (on page 2)) and view the saved files on your computer. The files will be saved on the SD card in the IC-7610\Capture folder. Or, you can view the saved files on the radio by going to Menu > Set > SD Card > Screen Capture View (on page 1). The files will be saved on the SD card using the file name format of yyyymmdd_hhmmss.png.

Here's a screen cap I just took of my radio:

 

[jazzboypro]

How are you measuring SWR with your rig? In the image you attached, it shows you were in LSB mode when you were transmitting. There is no carrier on SSB. The output of the radio depends on how loud you speak and how the mic gain is set. Were you whistling into the mic to get a reading on the power meter?

If you look at the images prcguy added, you'll see he was using FM mode. This is a much better way to do it since when you squeeze the mic, you're putting out a full 100W carrier with no need to provide any audio.

Good point. The mic gain and drive gain are at their default values (50%). So i selected FM and the frequency is set to 3780. Here are the results:

Radio set to 50W and tuner off
SWR 2.7 power out 50W

Radio set to 50W and tuner on
SWR 3.2 power out 35-40W

Radio set to 100W and tuner off
SWR 2.7 power out 50W

Radio set to 100W and tuner ON
SWR 3.5 power out 35-40W

 

[jazzboypro]

Here's an IC-7610 tip that makes capturing the display a piece of cake:
1. Insert an SD card into the SD card slot on the front of the radio.
1a. Format the SD card in the radio.
2. Go to Menu > Set > Function > Screen Capture [POWER] Switch (on page 6) and make sure it's On.
3. When you want to capture the display, just tap the POWER switch. The radio will write the current display to the SD card as a .png file.
4. You can take the card out of the radio (go to Menu > Set > SD Card > Unmount (on page 2)) and view the saved files on your computer. The files will be saved on the SD card in the IC-7610\Capture folder. Or, you can view the saved files on the radio by going to Menu > Set > SD Card > Screen Capture View (on page 1). The files will be saved on the SD card using the file name format of yyyymmdd_hhmmss.png.

Here's a screen cap I just took of my radio:
View attachment 148645

Thanks for the tip

 

[tweiss3]

Good point. The mic gain and drive gain are at their default values (50%). So i selected FM and the frequency is set to 3780. Here are the results:

Radio set to 50W and tuner off
SWR 2.7 power out 50W

Radio set to 50W and tuner on
SWR 3.2 power out 35-40W

Radio set to 100W and tuner off
SWR 2.7 power out 50W

Radio set to 100W and tuner ON
SWR 3.5 power out 35-40W

Cutting power over 3:1 sounds correct, but having 50W target outputting at expected, but nothing above 50W target achieving anything above 50W sounds like something died in the radio.

EDIT: If you have a dummy load, test into the dummy load with an external meter. (Radio->Meter->Dummy load)