Tuning scope in box antenna

[Dr. Rich Russel]

All,

I got a nanovna and found that the dish is not tuned to 1420 mhz.

Is there a way to tune it?

Rich

[Stephen Arbogast]

Are  you   using  an  lna?  What is  it's  band pass?

When  my  observations   are  way  off   I  whip   out  my  trusty  Tiny Spectrum Analyzer  and use  it to send a  signal  to my  Discovery  Dish....... not  saying  it  is  accurate ..  gets me  in the  ball park .

Here is  a link  to  the Tiny Spectrum Analyzer  It is very  helpful    since  can send  signals  too.....   I  have found it  a  cool toy and  gets me in the ball  park....  https://www.tinysa.org/wiki/

[Dr. Rich Russel]

I am using the nano vna h4. It says that the swr at 1420 mhz is >20.

Can the dish be tuned?

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[Stephen Arbogast]

First of   all  what   dish   are you using?  

[Dr. Rich Russel]

Amazon.com

Amazon.com

1.4 ghz mesh antenna - see amazon link above. I got 2 of these for my phased array project. One of them had a 1.4 swr at 1420 Mhz, the other had 22 swr.

I plan on taking the feed apart tomorrow to see if there is anything that can tune it.

https://groups.google.com/d/msgid/sara-list/d6eeba51-7541-482f-87c8-2a38ec2cb40dn%40googlegroups.com

.

[Stephen Arbogast]

First of all  ... in my opinion the  old  dish   used in  scope   in a  box  is  not  a good  choice  ....    meant  for  wifi...   A  better choice  is the  new  Discovery  Dish  with lna   for  hydrogen line.  so  far    I  am getting    good  results...   But  results  do not  come auto-magically..   One must learn  data science  to  remove   spurs .

[Mike Otte]

Rich,  

The 22 swr  looks to me like a bad connection .   Esp when you have  a twin at swr 1.4.

Mike

To view this discussion visit https://groups.google.com/d/msgid/sara-list/3e862e47-395a-4f32-a1a6-2620d2bc6e95n%40googlegroups.com.

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Mike Otte W9YS

[Alex P]

Rich,

 Disassemble and see if there is a bad electrical connection .. you can pull out the black plastic  "T"  feed part from the aluminum square tube .

 It splits in half to expose the dipole elements  ( also  measure the resistance from the feed elements to the input connector )

The Disco_Dish uses a more shallow dish with a fixed LNA . It works fine with satellite signals,  

but it is not optimized for low level RA reception as the f/D and dipole provide high RFI exposure and ground noise spillover .

Alex P

HLine3D

[Lester Veenstra]

Yes, but reports are of minimal or no improvement.

Can we see a Smith Chart picture of what it looks like, measured at the feed point (the cable terminating at the back of dish—SOL cal at that point, not a VNA), with marker it 1425.

 

Lester B Veenstra  K1YCM  MØYCM  W8YCM   6Y6Y W8YCM/6Y 6Y8LV (Reformed USNSG CTM1)

les...@veenstras.com

 

452 Stable Ln

Keyser WV 26726 USA

 

GPS: 39.336826 N  78.982287 W (Google)

GPS: 39.33682 N  78.9823741 W (GPSDO)

 

 

Telephones:

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[Dr. Rich Russel]

All,

Found bad connection t antenna - SWR now at 1.4.

Thanks

Rich

https://groups.google.com/d/msgid/sara-list/3e862e47-395a-4f32-a1a6-2620d2bc6e95n%40googlegroups.com

.

[Dr. Rich Russel]

Recommend everyone check out the dish antennas with a VNA. The new antennas look good with a flat SWR from 1 - 1.5 GHz.

Thanks Alex for the recommendation!

See SWR response in attached picture.

Rich

https://groups.google.com/d/msgid/sara-list/1698616871.1195815.1758913373878%40mail.yahoo.com

.

[b alex pettit jr]

No Problemo    With such a Huge error, it had to be something 'simple' ...

[Dr. Rich Russel]

SWR looks flat from 1 Ghz to 1.5 Ghz. See picture.

Fixed!

The center pin had broken off the antenna. Thanks Alex!

I now have a 1.4 swr. At 1420 Mhz.

I recommend that everyone test their antennas with a nano vna before use. Or at least take them apart and check the connection.

I am checking the rest of my antennas.

Thanks for agreat troubleshooting session.

Rich

To view this discussion visit https://groups.google.com/d/msgid/sara-list/102e01dc2ef6%24d3b577b0%247b206710%24%40com.

[Dr. Rich Russel]

Fixed!

The center pin had broken off the antenna. Thanks Alex!

I now have a 1.4 swr. At 1420 Mhz.

I recommend that everyone test their antennas with a nano vna before use. Or at least take them apart and check the connection.

I am checking the rest of my antennas.

Thanks for agreat troubleshooting session.

Rich

To view this discussion visit https://groups.google.com/d/msgid/sara-list/102e01dc2ef6%24d3b577b0%247b206710%24%40com.

[Dr. Rich Russel]

Swr looks flat from 1 Ghz to 1.5 Ghz. See picture.

[Stephen Arbogast]

Yes, I have heard  a  number of times that  SMA connectors   are not sturdy/reliable.   I have  two  coax  cables  with  broken   make   SMA connectors.   

[Don Latham]

Not robust, yes. The trick is, once the tip of the pin is engaged, the nut should be tightened without turning the pin, that is, the cable should not rotate. for on/off use, type N or type BNC at lower freq's preferred.  M-F Adapters or short cables with F-F on one end can be used if equipment comes with SMA's or on equipment to be used a lot, Recalibration sometimes necessary.  Finally, at great cost, commercial providers can provide robust connectors. 

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From: "sara" <sara...@googlegroups.com>
To: "sara" <sara...@googlegroups.com>
Sent: Saturday, September 27, 2025 4:57:50 PM
Subject: Re: Fw: [SARA] Tuning scope in box antenna

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

[b alex pettit jr]

And using a small SMA connector on LMR400  ( 0.4" dia ) type cable is a formula for potential connector damage to its lack of flexibility.

[Don Latham]

The ridged part of the connector at the end of the cable is designed to be held while the connector is pushed gently into the socket. The nut is free to turn at this point and can secure the connection in place. The point is that the socket has to be small and delicate to maintain impedance match and is not made for a rotating pin.  It's true, the cable is probably too large and certainly has to be supported, traveling away from the connection in line with it. This setup was made to be connected maybe once or twice, not repeatedly, and is actually forced by the devices it is to be used on. Hope this helps.

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From: "sara" <sara...@googlegroups.com>
To: "sara" <sara...@googlegroups.com>

Sent: Sunday, September 28, 2025 5:56:11 AM

Subject: Re: [SARA] Tuning scope in box antenna

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