[OFARC] Questions about antenna tuning

[sc flowers]

Hey Don,
Good afternoon.  First of all, welcome to the hobby!  It’s a great hobby and there are just so many areas to learn in the hobby that I’m sure you’ll have a good time.

Now for the question at hand, I’ve found that SWRs greater than 1:2 are probably what you don’t want to push power through.  The cutoff of 2.0 for SWR is what my current transceiver flags as being too high.  Actually, the Foundation exam that the UK radio amateurs take has the cutoff at 1.5, which is tighter than the 2.0 just mentioned.  I think that 1.5 is a bit too tight, it’s a good ideal to strive for but not a deal killer, IMHO if my SWR is between 1.5 and 2.0.

Now the 6m, 10m and low end 15m SWR readings you highlighted in red in your spreadsheet are above the SWR = 2.0 cutoff (I mean what is commonly referred to 1 to 2, or 1:2, or 1:2.0).  So I wouldn’t push power through those bands when the SWR is that high.  I’d say consider making a tuning circuit or buy a manual tuner or an automatic tuner.  Maybe at a hamfest you can find a good deal on a working MFJ manual tuner and that would do the job.  Nice spreadsheet BTW.

Alternately, you could put up a separate antenna to work on 15, 10, 6m bands.  Note that antennas for bands higher or equal to 12meters are not really that big.  I’ve got a dipole for 12m taped to the inside of my shack so it’s not that big or unwieldy.  It’s your choice on what to put up of course but my point is that for the bands that are giving you grief, a smaller antenna may give you a good SWR, work just fine in transmission, and keep your transceiver happy as far as minimal reverse power.  You’ll find that the reverse power, as opposed to the forward power going to your antenna, can be detrimental to your transceiver.  Specifically, I hear that reverse power can damage your final FETs in your transceiver, though I’ve never had to replace final FETs.  Knock on wood.

As far as why some bands show high SWR and others don’t, I’d say it’s due to the resonant characteristics of the particular antenna.  For example, this is the 3-30MHz sweep of my EndFed Halfwave (EFHW) antenna deployed in 2023.  Notice how the SWR dips don’t all correspond perfectly to the ham bands, highlighted in light gray.  BTW, my current EFHW antenna is much worse than this one from 2023…

Well, hope that helps and again Welcome to the Hobby!

73,
Stephen (W2WF)
 



> On Oct 15, 2024, at 5:47 PM, Don Davis via OFARC <ofarc at mailman.qth.net> wrote:
> 
> Hi to All,
> 
> I'm only a 2-year-old at this hobby, so I hope y'all can help with this:
> 
>> My first HF antenna got destroyed by the derecho. So, before the hurricane came, I took down the new MFJ 1836H cobweb 40-6M antenna. I recently installed it back up again and retuned it about 7 feet above ground. Raising it up on a mast about 20 feet above ground changed some of the SWR readings. Anyway, I have attached a spreadsheet of the readings on various bands. Notice the 6m and 10m bands have high SWR readings especially at the low end of the band and the high end. Also, the low end of the band on 15m is high. Since I have a general license, I used those frequencies as a band plan, trying to tune at the center frequency. I used an MFJ 269 antenna analyzer. Are these values too high for an antenna tuner? Is this to be expected on 6 and 10M bands?  I don't understand why the high edge of the 15m band has a high SWR? Do I need to retune these bands?
> Thanks to all for your help,
> 
> Don KI5WWD
> <latest MFJ 1836H tuning final.xlsx>______________________________________________________________
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