Alex's yagi antenna -

[Robert Lucas]

I just used my nanoVNA to check the antenna and the result was not as expected. The antenna has been out in the weather for almost a year. I'm assuming it is time to dis assemble the antenna and clean all of the contacts. Any suggestions on how to clean and reassemble? My guess is galvanic action between the aluminum plates and the stainless steel spacers. Just tightening the nuts might not create the gas tight connection. 

Cheers

Rob

[Alex P]

The Spacers are also Aluminum.  

Measure the DC resistance from end to end elements ..  It must be less than 1/2 Ohm or so or else YES, it will not properly function.

Totally Disassemble and clean every interface with sand paper, alcohol & wipe off any debris.

    The SMA to patch disk connection needs close attention.  

        SMA connectors and LNAs are Not Waterproof, nor was that intended to be an Unprotected All Weather Antenna .

( didn't you 'redesign' the Patch Feed disk as you believed it shouldn't be 'shorted' to the Reflector ?  Check Your Re-Repair Work  )

Alex

[Robert Lucas]

Alex

I put the antenna back to your design after you explained my mistake. It worked and I'm doing the ezCon to analyize the scans. I want to do scans to fill in what I missed. I thought it would be good to verify the system. And document the system. 

thanks 

Rob

[Don Latham]

clean all contacting surfaces, apply stuff made for using aluminum household wiring. It will help dissimilar metal contacts.

can't remember the name... Don't forget that dissimilar metal contacts with corrosion are diodes.

Don

 

------------
Don Latham
PO Box 404,
Frenchtown, MT, 59846
406-626-4304

 

---

From: Robert <roblu...@gmail.com>
To: Society <sara...@googlegroups.com>
Date: Tuesday, 3 February 2026 10:53 PM MST
Subject: [SARA] Alex's yagi antenna -

I just used my nanoVNA to check the antenna and the result was not as expected. The antenna has been out in the weather for almost a year. I'm assuming it is time to dis assemble the antenna and clean all of the contacts. Any suggestions on how to clean and reassemble? My guess is galvanic action between the aluminum plates and the stainless steel spacers. Just tightening the nuts might not create the gas tight connection. 

 

Cheers

Rob

 

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[Robert Lucas]

Alex

I measured the resistance at the sea connector and it is .3 ohm I added the 50 ohm 6" cable and the resistance is .7 ohm. I used the nanoVNA and  the antenna is spot on the 1.42.

Who could ask for more. I don't think I need to clean the antenna elements. 

I was. having problems getting ezCol to run and I solved that issue also. 

I still need to do the analysis for the previous scans to see where I need to point. 

Thanks 

Rob

[b alex pettit jr]

Rob, 

The Antenna is SPOT ON !

You use a 6' cable between the Antenna and the LNA ?

What Type of  Coax ?

Alex 

===============================

On Wednesday, February 4, 2026 at 11:53:44 PM EST, Robert Lucas <roblu...@gmail.com> wrote:

Alex

I measured the resistance at the sea connector and it is .3 ohm I added the 50 ohm 6" cable and the resistance is .7 ohm. I used the nanoVNA and  the antenna is spot on the 1.42.

Who could ask for more. I don't think I need to clean the antenna elements. 

I was. having problems getting ezCol to run and I solved that issue also. 

I still need to do the analysis for the previous scans to see where I need to point. 

Thanks 

Rob

.

[Robert Lucas]

alex

I think the telescope is working. Any comments on doing better?

Rob

[b alex pettit jr]

Rob,

I am unfamiliar with this software .. .. Looks okay

Alex

=====================================

[b alex pettit jr]

What type of Coax are you using between the Antenna and LNA ?

[Robert Lucas]

Alex

Bingfu from Amazon is the cable I use. I also use the same brand of cable but longer from Sawbird to SDR.

Rob

[b alex pettit jr]

What is the Model Number ?  RG-58 LMR400  RG213 ....??

[Andrew Thornett]

Before you need the following, there is a caveat. If all you want is 6 inches of cable then ot probably doesn't matter what coax you use as the cable is so short. But for longer runs the following is true.......

The cable you use needs to be rated for the wavelength you are observing.

RG58 is a no-no for hydrogen line as not rated for this frequency and you will experience considerable loss of signal.

Cheap RG6 works surprisingly well.

But of you want good stuff then LMR240 is an excellent choice and for those with piles of money and who don't mind thick cable LMR400 is the bees knees.

Here are realistic attenuation figures at 1420 MHz (1.42 GHz):

Cable

Loss (dB / metre)

Loss (dB / 10 m)

Loss (dB / 100 ft)

RG58

~0.60–0.70 dB/m

6–7 dB

18–21 dB

RG6

~0.18–0.22 dB/m

1.8–2.2 dB

5.5–6.5 dB

LMR240

~0.24–0.27 dB/m

2.4–2.7 dB

7–8 dB

LMR400

~0.10–0.11 dB/m

1.0–1.1 dB

3–3.5 dB

(Values based on typical Times Microwave specs; manufacturers vary slightly.)

I have some cheaper KMR240 and KMR400 which has similar specs to LMR versions.

Andy

Sent from Outlook for Android

---

From: 'b alex pettit jr' via Society of Amateur Radio Astronomers <sara...@googlegroups.com>
Sent: Friday, February 6, 2026 7:52:59 AM
To: sara...@googlegroups.com <sara...@googlegroups.com>
Subject: Re: [SARA] Alex's yagi antenna -

 

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[Bob Aleksa]

Hi Mr. Pettit

 This is my first time writing to the Forum. I am a complete beginner to Radio Astronomy. I am also building the 21cm Disk Yagi PEX version that you designed. I have 3 questions about the assembly of the antenna. I thought I would ask these questions before I experimented too much and damaged other Antenna pieces.

 1) My daughter and her husband made the aluminum disks for me as a Christmas presented. Before I started to assemble the antenna, I checked all the measurements and saw that the Feed Point hole is at 20mm and not 25mm. I assembled the first 3 elements (to experiment and learn) like you explained in your Jan 15, 2025 posting on the Forum. Using a NanoVNA, I got a resonant frequency of 1427.25MHz instead of the 1440MHz you predicted and measured. I built the entire antenna to continue learning and to see what the resonant frequency would be. I got a resonant frequency of 1428.75MHz and an impedance of 54.3 Ohms. I did not see the predicted “pull down” by adding the other elements. Being in the experiment/learning mode is it possible to re-drill another Feed Point hole at 90 degrees to the wrong hole and would that work or do I just have to start over again making two new disks?

 2) In your instructions you stated to adjust the 13 mm spacing between the Reflector Element and the Patch Feed Element to adjust the resonant frequency of the antenna to 1420MHz. Do you increase or decrease the 13mm spacing to lower the resonant frequency? I know I can experiment to find out this answer but I do not want to damage the threads I made in the wooden dowel by taking the antenna apart multiple times so that is why I am asking.

 3) I have the same question for adjusting the 13^th Detector element to adjust the 50 Ohm Impedance of the antenna. Do you increase or decrease the 40mm spacing to lower the Impedance?

 Thank You

Bob Aleksa

 

PS

Ham Operators within SARA

I hope this next question is acceptable to the Forum. It is a non-Radio Astronomy question for all the Ham Operators that are members of SARA. Over the last couple of years I thought I have heard some members mention that they were involved with EME (Moonbounce). I am just starting to learn about EME. I would enjoy talking to anyone involved with EME offline from this Forum. 

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[Bob Aleksa]

Hi Mr. Pettit

 This is my first time writing to the Forum. I am a complete beginner to Radio Astronomy. I am also building the 21cm Disk Yagi PEX version that you designed. I have 3 questions about the assembly of the antenna. I thought I would ask these questions before I experimented too much and damaged other Antenna pieces.

 1) My daughter and her husband made the aluminum disks for me as a Christmas presented. Before I started to assemble the antenna, I checked all the measurements and saw that the Feed Point hole is at 20mm and not 25mm. I assembled the first 3 elements (to experiment and learn) like you explained in your Jan 15, 2025 posting on the Forum. Using a NanoVNA, I got a resonant frequency of 1427.25MHz instead of the 1440MHz you predicted and measured. I built the entire antenna to continue learning and to see what the resonant frequency would be. I got a resonant frequency of 1428.75MHz and an impedance of 54.3 Ohms. I did not see the predicted “pull down” by adding the other elements. Being in the experiment/learning mode is it possible to re-drill another Feed Point hole at 90 degrees to the wrong hole and would that work or do I just have to start over again making two new disks?

 2) In your instructions you stated to adjust the 13 mm spacing between the Reflector Element and the Patch Feed Element to adjust the resonant frequency of the antenna to 1420MHz. Do you increase or decrease the 13mm spacing to lower the resonant frequency? I know I can experiment to find out this answer but I do not want to damage the threads I made in the wooden dowel by taking the antenna apart multiple times so that is why I am asking.

 3) I have the same question for adjusting the 13^th Detector element to adjust the 50 Ohm Impedance of the antenna. Do you increase or decrease the 40mm spacing to lower the Impedance?

 Thank You

Bob Aleksa

 

PS

Ham Operators within SARA

I hope this next question is acceptable to the Forum. It is a non-Radio Astronomy question for all the Ham Operators that are members of SARA. Over the last couple of years I thought I have heard some members mention that they were involved with EME (Moonbounce). I am just starting to learn about EME. I would enjoy talking to anyone involved with EME offline from this Forum. 

On Friday, February 6, 2026 at 3:04:19 AM UTC-7 Andrew Thornett wrote:

[b alex pettit jr]

Hello Bob,

GREETINGS !

1)  1428.75 is Fine..  and Yes, the R component correlates to the radius from the edge of the center  hole. ( 0 ohms at center,,, ~ 500 ohms at outermost edge )

   54 Ohms is Not really an issue ..  but, if you want, just elongate the hole on the patch feed inwards 2mm & move the screw.

2) Decreasing the distance Increases the Fn .. changing to 12mm might raise it  10 MHz

3) The outermost Director adjusts the Reactance part of the Impedance .. longer  increases the Capacitance  ? ( unsure )

( FYI, if you put some candle wax on the threads of the dowel, it makes threading & adjustment Much Easier )

Cheers,

     Alex P

[Nancy]

Hi Alex,

Thank You for your response. It seems like my Frequency of 1428.75MHz and Impedance of 54 Ohms are good to continue learning.

I have one question about your response. You mention elongating the hole on the Patch Feed "inward" a couple of mm. Since the hole was placed at 20mm instead of 25mm, going inward would now place the hole at 18mm. I would have thought that the hole should be elongated outward not inward. Can you please explain why "inward" would be proper?

Thank you

Bob

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[b alex pettit jr]

 I misread that I thought it was too far Out.. but if you are getting 54 ohms, 

I'd just wait & fully assemble the system,  then test

Alex

[Nancy]

Hi Alex,

Thanks for your help.

Bob

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[b alex pettit jr]

Hi Bob,

Here's the quick test which will verify all is okay :

The difference  between 10K cold sky & 290K Earth s/b in the 5 dB range.

If you get a good number, forget about what the VNA says :)

Alex

On Saturday, February 7, 2026 at 05:53:13 PM EST, Nancy <bob.na...@gmail.com> wrote:

Hi Alex,