[BVARC] Antenna help
Dominic Mazoch
domemt at juno.com
Wed Jun 19 13:55:46 CDT 2024
Suggestion:
What band are you working?
If you have a 17' telescope whip, you can extend it to 1/4 wavelength for bands 6-20M and bypass the coil.
On 6 and 10, you can extend to 1/2 wavelength. At 1/2, ground is nice, but not mission critical.
And I did get the higher power rated coil. That seems to help.
Dominic Mazoch
Please note: message attached
From: Stephen Flowers via BVARC <bvarc at bvarc.org>
To: Andre Pollard <apollard310 at gmail.com>
Cc: Stephen Flowers <s.c.flowers at comcast.net>, BRAZOS VALLEY AMATEUR RADIO CLUB <bvarc at bvarc.org>
Subject: Re: [BVARC] Antenna help
Date: Wed, 19 Jun 2024 10:19:58 -0500
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Andre,
Good morning. Glad that the three 33ft radials improved things. I’d say beyond that further improvements are probably in the coil itself. Maybe it’s not giving enough inductive load. This is what my Wolf River Coils (WRC) looks like. The coil length is larger than what I understand yours to be. Yours seems to be more like a shorty coil from WRC.
Would it be possible to add more inductive load to your setup?
73,
Stephen (W2WF)
?
> On Jun 18, 2024, at 8:34?PM, Andre Pollard via BVARC <bvarc at bvarc.org> wrote:
>
> Well, the rain broke and I tried 3 33' radials. That helped, but the best I can achieve is a 2.5 SWR and 72.3+j53.9 inductive on the Smith chart. Much better, and tuneable with the G90, but I was hoping for a little better. I tried adding the 10' radials but that didn't make a difference and I don't want to tear them apart to make another 33' radial.
>
> Interested in the collective wisdom on the above. Or is there another check I should be running Rick?
>
> Was hoping to get this going for times when an EFHW in a tree isn't possible (or allowed); I'll be doing some hiking in the mountains and the park there may not like wires in trees. Higher up, there aren't any tall trees either. At the cabin, I'll throw up the EFHW, and hopefully can work you guys at Field Day.
>
> Andre
> W4SFZ
>
> On Tue, Jun 18, 2024 at 7:28?PM Andre Pollard <apollard310 at gmail.com <mailto:apollard310 at gmail.com>> wrote:
>> I typically try to get a combination of lowest SWR at my chosen center frequency with the widest SWR curve. Then check impedance on the Smith chart at the center frequency. I'm using a nanoVNA, I don't have a grid dip meter. Impedance in the best case i've gotten is around 200 ohms on the inductive side of the chart (which explains why my body capacitance affects it so much it would seem). VNA was calibrated for the 6-8 mhz range before starting.
>>
>> I'm tapping the coil when adjusting by jumping from the feed to higher up on the coil. Just to try, I jumped from the antenna side to the coil. not a lot of difference, but I didn't have the Smith up then. I need to leave SWR and Smith on I think to get more information, rather than switching.
>>
>> When I move my hand close, the frequency of the SWR dip drops (as does the SWR). I didn't think to check the Smith when doing that. Right now I wouldn't consider it resonant on 40 LOL. But the calcs say it should be. They assume an effective ground radial system (among other things).
>>
>> My next try will be with a couple of 33 ft radials to see if that helps like several folks have pointed out. Once it stops flooding here that is.
>>
>> Thanks for all the input guys- Happy for any suggestions you have.
>>
>> Andre
>> W4SFZ
>>
>> On Tue, Jun 18, 2024 at 5:11?PM Rick Hiller via BVARC <bvarc at bvarc.org <mailto:bvarc at bvarc.org>> wrote:
>>> Questions......
>>>
>>> What do you mean "tuned" to 7.2?
>>>
>>> Are you feeding it at the base of the coil? Have you tried moving the feed point up the coil?
>>>
>>> What frequency change do you see when moving your hand close?
>>>
>>> Here is where just knowing the SWR is not what you need. What is the feed impedance when measured at the feed point? Lower than 50 ohms or higher? Reactive?
>>>
>>> Is the antenna system resonant on 40? How do you know? Do you have a GDO?
>>>
>>> What are you using to measure SWR? Maybe the analyzer has what you need as far as measurements required.
>>>
>>> Sounds like you are having fun. GL...Rick W5RH
>>>
>>> ps...just saw Chris's note about the GP. You might want to make a more lengthy or resonant elevated GP system to see how that affects it.
>>>
>>>
>>>
>>> On Tue, Jun 18, 2024 at 4:39?PM Andre Pollard via BVARC <bvarc at bvarc.org <mailto:bvarc at bvarc.org>> wrote:
>>>> I normally use a 5’x8’ faraday cloth which works fine on 20 and up. I made up 16 radials 10 feet long to try that and saw no difference.
>>>>
>>>>
>>>>
>>>>> On Jun 18, 2024, at 4:24?PM, wb5itt <wb5itt at att.net <mailto:wb5itt at att.net>> wrote:
>>>>>
>>>>> ?
>>>>> What kind of a ground system do you have?
>>>>>
>>>>> Chris WB5ITT
>>>>>
>>>>>
>>>>>
>>>>> Sent via my Samsung Galaxy S10e, an AT&T 5G Evolution capable smartphone..so there! ?
>>>>>
>>>>>
>>>>> -------- Original message --------
>>>>> From: Andre Pollard via BVARC <bvarc at bvarc.org <mailto:bvarc at bvarc.org>>
>>>>> Date: 6/18/24 4:19 PM (GMT-06:00)
>>>>> To: BRAZOS VALLEY AMATEUR RADIO CLUB <bvarc at bvarc.org <mailto:bvarc at bvarc.org>>
>>>>> Cc: Andre Pollard <apollard310 at gmail.com <mailto:apollard310 at gmail.com>>
>>>>> Subject: [BVARC] Antenna help
>>>>>
>>>>> I need one of our antenna gurus to give me some input-
>>>>>
>>>>> I have an 18'-4" telescoping antenna I have been using when camping. By adjusting length, I can get it to tune at <1.5 SWR on all bands 20M and above. So far so good, but when do we ever leave well enough alone.
>>>>>
>>>>> I'm getting ready to travel for a while, and wanted to extend the range down to 40M. So I used the calculators at Coil-Shortened Vertical Antenna Calculator (66pacific.com) <https://www.66pacific.com/calculators/coil-shortened-vertical-antenna-calculator.aspx> to determine the necessary coil. It said I need 4.9 mH. I made the coil per the calcs one the same site, using a 1.9 inch diameter PVC pipe. I'm running it bottom-loaded.
>>>>>
>>>>> By tapping the coil a couple of turns down, I can get it to tune to 7.2 mhz, but the SWR is >6. If I put my hand very close to the coil , the frequency shifts (expected), and the SWR drops to 1.2. So I tried adjusting the length and tapping different turns, never better than 4 SWR on any frequency around 7 mhz. However, if I get my hand near the coil, SWR drops.
>>>>>
>>>>> Thinking this meant I needed capacitance, I tried a hat to the whip, with several different designs and sizes. Changes frequency, but horrible SWR still.
>>>>>
>>>>> Bypassing the coil I can adjust the whip and get great SWR on 14 mhz and above. So, I don't think it's a problem with the coax (20 feet of RG8X) or nanoVNA.
>>>>>
>>>>> Google shows up all sorts of sites showing making a coil loaded shortened vertical like i'm trying. None mention the issue I'm seeing as a problem.
>>>>>
>>>>> I'd appreciate any input, I've been 'learning' on this for a couple of days now and haven't gotten it to work yet.
>>>>>
>>>>> Thanks,
>>>>> Andre
>>>>> W4SFZ
>>>> ________________________________________________
>>>> Brazos Valley Amateur Radio Club
>>>>
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>>>
>>>
>>> --
>>> Rick Hiller W5RH
>>> e-mail: rickhiller73 at gmail.com <mailto:rickhiller73 at gmail.com>
>>> Cell/VM/Text: 832-474-3713
>>> Physical: 9031 Troulon Drive
>>> Houston, TX 77036
>>> ________________________________________________
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>>>
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