Antenna whip cutting

Aaron S

Aaron S

Active Member
I’m getting ready to cut my new antenna for the frequency 411.2500. The data sheet specifies a length of between 31.7 and 32.0 mm for that frequency. I few questions about this:

First, how tight are those specs? Can I just trim to 32.0 mm and call it good? I don't know if my hacksaw skills are good enough to sub-millimeter levels.

Second, where is the length measured between? The datasheet is a little vague to me. Is it between A and B, or A and C? I ask because it talks about sliding the antenna around in the cone at C after you've trimmed it.

Lastly - when I'm done, how do I measure the VSWR the datasheet talks about, so I can see if it's all tuned in optimally? Is that built into one of the scanners in the TLS?

IMG_20200611_075800.jpg
 
Aaron S

Aaron S

Active Member
Adam said:
A-B is how I understand it.
Click to expand...

That's how I understand it too, but it doesn't make sense. Shouldn't the length be measured along the exposed portion of the whip, and not include those parts covered by the cone? You don't count whatever's under the phasing coil, but you do count what's under the base mounting cone? Seems kind of arbitrary.

Also, if it's not referring to the exposed section of the whip, why do the instructions say to cut it a bit longer and make the final adjustment by moving the whip up and down in the adapter? That would negate any precise cut you made.

This part is also confusing: the chart on the instructions says for a frequency of 422.5 MHz (for example), "CUT WHIP" is 11.5 inches or 29.2 mm. Problem is, 11.5 inches is 292.1 mm. So is this the amount I cut off, or the amount to remain?

Maybe I'm just dense, but this is all very frustrating and you only get one shot to cut that whip.
 
Last edited:
Vladimir Zhukov

Vladimir Zhukov

Well-Known Member
JAVAD GNSS
Hello Aaron,
Measure the length of the rod cut from the lower edge of the phasing coil to the end of the whip as it is shown in the picture.
http://download.javad.com/sheets/UHF_Whip_Antenna_5dB_NMO_Datasheet.pdf

there is 29.2 cm in the example, but not mm.

It is not easy to measure to one point and cut to another. Therefore measuring and cutting points should be the same.

VSWR measurement is the most serious part of the antenna tuning, as it needs special equipment.
You can cut according to the table, it would give better VSWR versus to the initial one.

We recommend specifying an operating frequency at the time an antenna is ordered, so we can tune for you at the factory. This is a free of charge service.

Regards,
Vladimir
 
Aaron S

Aaron S

Active Member
The sheet that came with my antenna has an error and all columns are labeled "mm" - the one you posted has all columns listed as "cm". Big difference.
I wish I'd known about the antenna tuning service when I'd ordered it. I only use one frequency.
 
Vladimir Zhukov

Vladimir Zhukov

Well-Known Member
JAVAD GNSS
Hi Aaron,
please send a picture of what was included at the factory, so it could be corrected asap.
Maybe we send you a new antenna tuned for your frequency and you return what you have if you did not use it yet?
 
Aaron S

Aaron S

Active Member
That's a great idea! I haven't touched the antenna yet - it's still pristine and new. If that would work, please send me an RMA and address.

Here is a PDF of what was included, please disregard the notes on page.
 

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  • antenna sheet.pdf
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A

Andrey Simonov

Active Member
JAVAD GNSS
Dear Aaron,
For opening RMA we need to know OLO, could you please send us any serial number of unit which included to this OLO.
Best regards, Andrey.
 
A

Andrey Simonov

Active Member
JAVAD GNSS
Dear Aaron,
Please confirm, can we use this information below for shipment to you?
USDA Forest Service
Joyce Rairdon
Chippewa National Forest
200 Ash AVE NW Cass Lake, MN 56633 U.S.A.
Phone: 218-335-8695, Fax: 218-335-8641
Best regards, Andrey.
 
Aaron S

Aaron S

Active Member
Andrey Simonov said:
Dear Aaron,
Please confirm, can we use this information below for shipment to you?
USDA Forest Service
Joyce Rairdon
Chippewa National Forest
200 Ash AVE NW Cass Lake, MN 56633 U.S.A.
Phone: 218-335-8695, Fax: 218-335-8641
Best regards, Andrey.
Click to expand...

That is correct. The antenna info is shown in the photo below. It has an extra-long cable, I don't know if that affects your tuning but I will send it along with the antenna in it's original shipping box. Just let me know what paperwork to include and where to send it for tuning.
 

Attachments

  • IMG_20200618_104930.jpg
    IMG_20200618_104930.jpg
    1.4 MB · Views: 325
Aaron S

Aaron S

Active Member
I'm sorry, I think I misunderstood. You are shipping the adjusted antenna to me first, then I'll send back the one I have. Is that correct?
 
A

Andrey Simonov

Active Member
JAVAD GNSS
Dear Aaron,
Please send only UHF Antenna, 5/8, 5dBd gain, NMO.
Please do not send other items, extra-long cable etc.
Please print an attached file and enclose it in the parcel with UHF Antenna.

GNSS RMA # JG20061818
Ship to: JAVAD GNSS Inc
Address: 900 Rock Avenue
San Jose, California 95131
Attention: Margil Anderson
Tel: + (408) 770-1770
Email: shipping@javad.com

Best regards, Andrey.
 

Attachments

  • RMA Instruction JG20061818.zip
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