Re: HF9V installation and tuning


Scott AC8DE
 

Fred,

 

Welcome to the fold.  Yours is a quite unusual installation; a type that I have no personal experience with tuning myself.  However, there have been a few through here over the years that did do over freshwater installations that had good results, which we talked though.  That said, I have definitely noted some significant issues that are correctable.  The thoughts are in no specific order, as I've written them down as I've looked at your photos.  Note, it would be a lot easier to dissect if you would use the excel sheet found here.  Looking at the charts doesn't give exact info.  It's close, but an excel sheet is better.

https://groups.io/g/Butternut/files/Butternut%20Tuning%20Charts/AC8DE%20Antenna%20Tuning%20Chart%20Excel%2097-2003%20format.xls

 

First, I renamed your album to start with your call sign.  It's hard to find anything over time in a folder that doesn't start with the owner's call sign.

 

SWR is NOT in indicator of antenna efficiency, so let's get that out of the way first.  SWR is only a portion of the picture.  A dummy load has perfect SWR after all.

 

  • Feed point height:  The height of the feed point above the ground plane should be a maximum of 6", with 3" being optimum.  You have your feed point at 15.75" above the water level/ground plane.  This is generally problematic for antenna tuning, but really problematic for efficiency.  Think of the results if you separate the two halves of a dipole by more than a couple inches.  Same thing with a vertical and its ground plane, as the ground plane is the "other half" of the antenna.  However, even with this high feed point, it may still be quite workable in an above water install, just understand the effect on bandwidth and efficiency.
  • Coil positions - This appears to be your biggest problem. It appears you have your 80M and 40M coils switched.  The coil with more turns (about 16-17) of the two is the 80M coil, which belongs BELOW the insulator.  The 40M coil typically has about 10 turns.
  • 80M:  If I visually drop the lowest SWR to 1:1 (which happens with Q coil adjustment), it appears that you are getting about 50 KHz of bandwidth below 2:1 by my estimate.  It should only be about 20-25KHz.  This is usually indicative of poor ground plane coupling/effect for the ground and hence, low antenna efficiency.  The usual advice is to install more radials, but in your case, I have no suggestion.  Drop the feed point as much as possible.  These comments may change considerably when you get the coils swapped.
  • 40M:  The first thing that jumps out and bites me is that your 30M coil assembly is tapped in the completely wrong place on the 40M coil.  (Although this is the wrong coil to begin with as installed.)  Its proper starting point is the 3rd or 4th turn down from the TOP of the 40M coil; usually the 4th.  I'd bet my house that the wrong coil and tapping point combination is causing your 40M problem and an improper tune of 20M.  Probably does some weird stuff to 30M as well.  These comments may also change considerable when you get the coils swapped.
  • What am I seeing in this photo?  https://groups.io/g/Butternut/photo/183823/14?p=Created,,,20,2,0,0  Is this a guy point?  If so, what is the big metal bracket you are using?  Seems like some massive overkill that adds capacitance and stress.  All you heed is a hose clamp and some D-rings and the smallest rope you can get.  There is very little wind loading on a Butternut, so small guy lines and light brackets are all that is needed.  It doesn't need to be any more than this, which has withstood 70 MPH winds. https://groups.io/g/Butternut/photo/25953/18?p=Created,,,20,2,0,0
  • Once you get the 80, 40 and 30M coils all sorted out, things will be quite a bit different.  If there are any questions on tuning procedure, look at the latest version of the instructions here. https://groups.io/g/Butternut/files/Butternut%20Manuals%20-%20New%20DX%20Engineering%20Versions/HF6V%20&%20HF9V/BUT-HF9V_Rev3.pdf
  • 10M: The tune for 10M should NOT be that flat.  You should just barely pick up all the band below 2:1 and usually the ends of the band are just slightly above 2:1. This is probably the effect of the higher feed point.  Not a deal breaker, but again, is a sign of poor ground plane coupling.
  • I am not seeing any sign of anti-oxidant compound on your tubing joints or other aluminum junctions at the coils.  This is going to be problematic in short order, especially over water.  DX can sell you what you need.
  • And finally, for the love of all that is holy, reform your 80M and 40M coils.  You are killing my OCD.  Doesn't affect function, but you're killing me.  LOL

 

I won't comment on the rest of the tuning until you get those coil position issues addressed, which is key.

 

73,

Scott AC8DE

 

 

From: Butternut@groups.io On Behalf Of Fred PA3FK
Sent: Tuesday, November 12, 2019 8:54 AM
To: Butternut@groups.io
Subject: [butternut] HF9V installation and tuning

 

Hi Experts,

Let me introduce myself a little bit first.

My name is Fred Koch, 61 years young, and radio-amateur since the 1980's.  Started my carreer as a Radio-Electronic Officer in the merchant marine so i should be aware of the theory of antenna's and tuning, however this was 40 years ago and i have not been very active in the hobby so my knowledge has faded a lot i notice. 

But recently picked up the hobby again and in the weekend of November 9/10 2019 i have installed a HF9V into the ditch behind my house and tried to tune it.
The antenna is installed into the ditch, and the ditch holds about 1 M water depth.  I first drove a 3,5 M pole into the earth and then mounted the base of the HF9V (Pole A) so it is about 40 cm above the water level. (see pictures in the album).
Note that the ditch is not a salt water ditch, however from reading on the internet, i have found several posting showing good results putting the HF9V up this way without using radials.
As a ex R/O i will be using CW only (with perhaps an incidental exception for SSB) so i am aiming to have the best SWR around the lower portion of the bands.

Assembly of the HF9V was feasible, however i do recognize that the instructions could be improved here and there but i think i got it right in the end.

And then the tuning begins.
I have a Mini60S as antenna analyzer and there are some strange results i would like your thoughts about. (see picture in my album where i uploaded the outcome of the scans i did)

To start from lowest to highest band 
6 M:  Min SWR (1,49) at 48900..  This weekend the dip was properly at 50.000 so it seems i need to tune the 6M wire a little again but overall this seems like an acceptable SWR graph
10M: Min  SWR (1,41) at 27850 and overall very flat.  Perfect (see Improved 10M scan)
12 M: Min SWR (2,64) at 26500. Way off. This is with 12M coil fully compressed (see pictures) as per initial tuning instructions. However when extending the 12 M coil nothing changes.
15M: Min SWR (1,45) at 20975 with enough bandwith so the 28.000 -28.100 is workable.  Fine with me
17M:: MIn SWR (1,33) at 18020. could shift it a litlle to make lowest swr at 18080.for the moment fIne with me.  Note picture 17M scan second The first shows a different result.  MIni60S reliable???
20M: Min SWR (1,39) at 14010. Fine with me
30 M: SWR of 2,6 around 10.100..  Strange graph with second dip.  For now workable. But what does it tell?
40 M:  Two scans that both are strange. One with no dip at all (second 40M) and the first with two real sharp dips at 6650 and 6750.   This important band is unworkable.  This is my main concern as i want to be able to work properly on 40 M
80 M:  Min Swr (1,33) at 3560. Should be shifted a little bit to the left (center frequency of 3520).   Adjusting the 80M coil should achieve this. 


I am very interested to better understand the complete lack of a reliable SWR graph on 40M.  Looks as if something is not compeltly right there that is beyond tuning.


Next is the 12 M.

Note: I have not yet adjuested the base coil Q for an even lower SWR on 80M. 

Looking forward to your thoughts on this.

Join Butternut@groups.io to automatically receive all group messages.