RE: 2.4 GHz ( 1.7 Ghz ) Antenna Adjustments for 1.42 ??
Lester Veenstra
I need to work these issues on an improvised test range but am not there yet.
I am skeptical of moving the feed point with respect to the dish, but will try that last. The focal point of a parabolic is independent of frequency. It could be the original design was not at true focus.
I plan to
1: Increase feed dipole to get resonate at 1.42
2: Will try flipping the “sub reflector” although not sure what that will buy. Distance between “sub reflector” and dipole may be more interesting.
The “sub reflector” is regally a reflector element in a two element yagi.
3: Line grid surface with mesh. This has the most promise.
Lester B Veenstra K1YCM MØYCM W8YCM 6Y6Y
452 Stable Ln (HC84 RFD USPS Mail)
Keyser WV 26726
GPS: 39.336826 N 78.982287 W (Google)
GPS: 39.33682 N 78.9823741 W (GPSDO)
Telephones:
Home: +1-304-289-6057
US cell +1-304-790-9192
Jamaica cell: +1-876-456-8898
From: b alex pettit jr [mailto:a_pet...@yahoo.com]
Sent: Tuesday, August 17, 2021 1:52 PM
To: m0...@veenstras.com
Subject: 2.4 GHz ( 1.7 Ghz ) Antenna Adjustments for 1.42 ??
Hello Lester,
I initially was planning on purchasing the 2.4 GHz variant of this antenna, but then some of these comments
extended my search, and eventual purchase of the Nooelec GEOS 1.7 GHz configuration ...
===========================================================================
THESE comments were posted related to repurposing a 2.4 GHz antenna to 1.7 GEOS GHz
1) Receives HRPT and GOES (HRIT/LRIT) just fine with slight modification. I simply installed a spacer mod to the metal V (note that inverting it is almost as effective and MUCH easier) and zip tied wire mesh to the grid. Note that the latter massively boosts gain. I literally used metal fencing to do this. You’ll want something around 19 gauge/0.5 inch mesh. You don’t want it too big or small though, or you’ll miss the intended frequency range. I forget the calculation but this thickness and hole size worked in it if you’re lazy like me and just want to get HRPT working. The wire mesh mod is not necessary for GOES at all, but can be implemented if you’re trying to absolutely min/max (optimize) your viterbi error rate. At the very least, I’d invert the feed so the V is pointing outward. For the spacer mod, I again forget the exact number, but a small piece of pool noodle foam, some string, and some slip knots worked surprisingly well for this. If you do go with the mod, make sure the V is pointing inward, as you don’t want to extend the dipole out too far. In essence, either flip the metal or do the spacer mod (not both). If the desired goal is HRIT/LRIT then that’s it. If it’s HRPT, then get to cutting and tying mesh down. Or just get a normal dish antenna like normal HRPT people. Or be like me and force something that’s not intended to work to work.
2) Will this also work in the 1679.70–1680.10 mhz frequency range for goes16 satellites?
Answer:
Yes, although for better results use a 2.5 cm spacer between the feed and secondary reflector.
3) I am interested in using this antenna for 1700-2200mhz b66 lte. Is this antenna capable of this range?
Answer:
You would need to invert the reflector and extend it by @ .5 inches.
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Then, I asked nooelec about the required modifications needed to adapt their 1.7 GHz antenna to 1.42 GHz H1
and just received this replay
Tasha (Nooelec)
Aug 17, 2021, 10:58 EDT
Hi Alex,
I've reviewed your question with our engineers and they have said that modifying the length of the antenna feeder is not the optimal way to receive at the SAWbird+ H1 frequency. The dimensions of the main reflector need to be modified as well to achieve the best reception. Unfortunately, we don't have any measurements related to this inquiry as the antenna was designed and tested for the purpose of GOES reception, not other applications.
The best practical way to find the best dimension is to gradually increase the arm length until the highest signal is received.
Please let me know if you have any further questions, thank you!Kind Regards,
Tasha C
===============================================================
Can You or Someone more familiar with GHz frequencies decipher these comments ??
I have an Extra Class amateur radio license and have successfully NEC modeled and built several 20m and 40m
antennas, but the GHz realm is a mystery..
WHY would the parabolic reflector shape and focus point be Wavelength Dependent ?
This may be useful information to any other builders of the " Scope in a Box " system .
Best Regards,
Alex Pettit
KK4VB
sara-...@veenstras.com
First try to determine the focal point using the simple process shown in the two attachments (both are the same process).
Do this across the short axis, and again, for the long axis.
Are the calculated focal distances the same, on both axis?
Lester B Veenstra K1YCM MØYCM W8YCM 6Y6Y
452 Stable Ln (HC84 RFD USPS Mail)
Keyser WV 26726
GPS: 39.336826 N 78.982287 W (Google)
GPS: 39.33682 N 78.9823741 W (GPSDO)
Telephones:
Home: +1-304-289-6057
US cell +1-304-790-9192
Jamaica cell: +1-876-456-8898
From: b alex pettit jr [mailto:a_pet...@yahoo.com]
Sent: Friday, August 20, 2021 10:55 AM
To: Lester Veenstra
Subject: Re: 2.4 GHz ( 1.7 Ghz ) Antenna Adjustments for 1.42 ??
Hello Lester,
I can NOT understand these measurements ..
The actual 'mechanical' focus of the antenna is nearly twice the distance at which the
antenna is located .. Can You Explain, Please ??
Thanks,
Alex
KK4VB