will this have enough bw for ssb - Page 1
Forum section: electronics / rf-microwave

author: p.larner
author_rank: Frequent Contributor
timestamp: November 05, 2023, 02:17:43 pm
content: i plan to build an octogon shaped magloop from 22mm dia copper pipe,total length will be 10m circumferance,would the bw be wide enough for a ssb signal on the top end of 80m,with a suitable cap?,thanks+73.

author: p.larner
author_rank: Frequent Contributor
timestamp: November 07, 2023, 05:44:44 am
content: no answer was a stern reply!.

author: A.Z.
author_rank: Super Contributor
timestamp: November 07, 2023, 06:17:14 am
content: https://www.eevblog.com/forum/rf-microwave/magnetic-loop-bandwidth/msg5154427<sigh>

author: iMo
author_rank: Super Contributor
timestamp: November 07, 2023, 08:43:40 pm
content: From 3.780 to 3.800 (dx segment) most probably yes.

author: Andy Chee
author_rank: Super Contributor
timestamp: November 08, 2023, 12:45:16 am
content: According to RJELOOP1.exe the bandwidth of your proposed loop is 1.8kHz. So not quite wide enough bandwidth for SSB.https://m0ukd.com/homebrew/antennas/magnetic-loop-antennas/YMMV

author: p.larner
author_rank: Frequent Contributor
timestamp: November 11, 2023, 01:49:45 pm
content: this is what i found see attached pdf.

author: iMo
author_rank: Super Contributor
timestamp: November 11, 2023, 02:16:12 pm
content: With a higher frequency - like 3790kHz in the mid of the dx segment I indicated above - you will get a little bit bigger BW.A 2-5kHz "antenna BW" does not mean you cannot do SSB qso there.That has less to do with the "audio BW" (3kHz for SSB).It only indicates your antenna SWR will be a little bit higher than 1.0 (for example) at your 5kHz BW edges. Up to 2.0 is all ok.What is important to know is the RF voltage -> 4600Vrms (the peak-peak voltage is much higher than that) and the RF current in the loop 21Amps rms (and that is with 100W only).You would need a tuning capacitor rated for that RF peak-peak voltage, and the capacitor must be without any sliding contacts, as the contacts will evaporate quickly (the RF current)You would need something special, there.. Like "vacuum variable capacitor for 10-15kV" (pretty expensive $300-$1000).Coupled with a stepper motor, remotely driven when you want to tune the antenna within the band..With a fixed frequency the fixed capacitor would be much easier to do, but sticking at a single frequency will make you happy for max one hour long at best, my bet

author: A.Z.
author_rank: Super Contributor
timestamp: November 11, 2023, 03:21:27 pm
content: wellhttp://ur4ll.net/#caps3_1

author: Andy Chee
author_rank: Super Contributor
timestamp: November 12, 2023, 04:36:40 am
content: Also if you can't afford a vacuum variable, you can build your own butterfly caphttps://www.ta2wk.com/high-voltage-diy-air-capacitor-for-magnetic-loop-antennas/You could even try to get some sheet copper laser cut into butterfly plates and make the capacitor out of copper.

author: Andy Chee
author_rank: Super Contributor
timestamp: November 12, 2023, 05:04:00 am
content: Quote from: A.Z. on November 11, 2023, 03:21:27 pmThat guy Alex UR4LL is based in Ukraine. Given the current conflict over there it might pay to check with him first whether he's open for business as usual (last I heard, he was).

author: Andy Chee
author_rank: Super Contributor
timestamp: November 12, 2023, 05:13:24 am
content: Quote from: p.larner on November 11, 2023, 01:49:45 pmBe aware. The loop calculator you used cites the ARRL Antenna book as its source. Apparently there is an error in the formula derivation, though I haven't personally checked (the derivation is beyond my math):https://owenduffy.net/blog/?p=1682Ok I just did a review. Your loop calculator has indeed inherited the ARRL formula error for calculating Quality Factor Q. This means bandwidth, voltage, and current calculations are all incorrect. The rest of the calculations look fine.

author: Bud
author_rank: Super Contributor
timestamp: November 12, 2023, 07:21:41 am
content: Max Gain Systems (mgs4u.com) sells vacuum variables (located in the US).

author: iMo
author_rank: Super Contributor
timestamp: November 12, 2023, 09:06:03 am
content: You may also use a standard old style tuning capacitor with several packets wired in series.That increases the voltage capability N times and eliminates any mechanical contacts as the current goes through the common rotor (an equivalent of the butterfly capacitor).See below the capacitor in my 6m band antenna (35cm diameter) with 4 packets in series. There is a small capacitor made of RG213 to get the variable capacitor into the band. Before that I had used an RG58 piece there and it caught fire within a couple of seconds after I pushed 100W CW into the antenna. Also the tuning with that capacitor is a nightmare, I am not using the magloop antenna anymore..