Topband: water saturated ground effect MA160V

[Guy Olinger K2AV]

Hmm,

Don't get low angle, high angle confused with sky wave.  Both low and
high angle are sky wave, as opposed to ground wave which is a
different mode of propagation that is always "local". You do not work
DX with ground wave.  Ground wave goes as far as you can hear 540-1700
kHz AM BC stations in the daytime.

Your change from 1:1 to 5:1 SWR is EXTREME, and indicative of a severe
problem SOMEwhere.  Dense and sufficiently long ground based radials
will not exhibit that kind of change.

And be careful not to credit 500 low power Q's in a 160 test to your
transmit antenna.  I've made 500 Q's in ARRL and CQ 160 tests running
100 watts on a purely awful antenna, but I attribute that to the EARS
on the other guy.  They WANT to have a QSO with you, and if they can
hear you JUST BARELY,  AT ALL,  you'll get their exchange because it's
points for them.

One guy in PVRC not so far from here makes 500, 600 contacts every
year in the 160 tests, running 5 watts QRP.  Tell me when you make 900
contacts in one of those tests running 100 watts.  At that level,
everything has to be working right... station, operator, AND the
antenna.

73, Guy



On Wed, Jul 20, 2011 at 1:08 AM, BRYON PAUL n0ah VEAL <bryonveal at msn.com> wrote:
>
>> Date: Tue, 19 Jul 2011 19:05:26 -0400
>> Subject: Re: Topband: water saturated ground effect
>> From: olinger at bellsouth.net
>> To: bryonveal at msn.com
>> CC: topband at contesting.com
> Guy,
>
> FB response to pick up on- We'll be in Costa Rica with the Youth DX
> Association from July 21-25th, so please look for us all- and I'll enjoy
> reading any follow up on this as time goes on-
>
> Today, all test were at the feedpoint, without the UnUnm including trying
> two different short feedlines of a few feet- They both showed the same- the
> minimum SWR is finally creeping up a bit, from 1:1 yesterday to 2.1:1 today-
> then it rained again-   I feel the ground soaked earth is causing some
> interesting measurements on the antenna.  Very unexpected.  In a few days,
> once we return to a scortched earth, it will be interesting to see what
> happens.  If the SWR goes back up to 5:1 or so without the UnUn in line as
> things dry out, that is, just measured at the feed point, this would be an
> interesting topic to discuss- If it remains low, then I'll just look at the
> loading coil - but since it rose up some today, I really feel the drying out
> saturated ground is messing with things- thx for all the awesome responses-
> This is a good topband antenna for small back yards from our view-
>
>> The change in SWR with the dampness is an indication of the
>> insufficiency of your radial system compared to a dense, commercial
>> grade radial system.
>>
> I disagree here in that adding the radial system incrased the SWR from 1:1
> to 5:1 when first installed last year showing it did make a significant
> improvement in the antenna's efficiency-
>> 26 buried radials would not be sufficient in any event, to insure
>> complete independence of the antenna from the wide variation in
>> ground-related effects. For there are either too few of them if they
>> are quarter wave, or too short if 26 radials are properly dense close
>> to the antenna. Even if all your radials are 1/8 wave which borders on
>> dense, use of only 1/8 wave in dirt as variable as you describe would
>> not prevent seasonal variation, as you would still have significant
>> ground interaction beyond the 1/8 wave. Further, if the radials are
>> not equal and evenly spaced, some portion of the ground field
>> cancellation benefit will be lost, the exposure to ground losses
>> increased, and therefore the variation is increased.
> Verdict is out here for us-but i appreciate the explanation-
>>
>> Further yet, given the shortened (30 to 36 feet) antenna, the
>> performance basically is 95% determined by the ground treatment, which
>> is why you can have huge variation with ground changes. Worse yet,
>> empirical evidence continues to accumulate that in typical ham
>> situations, and with reference to sky wave, that even the mighty NEC4
>> modeling methods ***UNDERESTIMATE*** ground losses UNTIL a DENSE,
>> commercial grade radial field is in use. Model results seem to play
>> truer to performance if one always starts with POOR ground assumptions
>> until a more optimistic estimate can somehow be PROVEN. Guess or hope
>> doesn't cut it.
>>
> Rersults do- we went from an average of 50 QSO's to between 500-600 in last
> year's ARRL and CQWW 160M contests using 100 watts- Record distance is
> making the ZL8X log with 100 watts.  No sky wave asperations here om- we DX
> (-:
>> The minus 6 dBi on the DX engineering page could easily be minus 9 or
>> even minus 12.
> No disagreement here->
>> There is a simple rule that is emerging with respect to on-ground or
>> buried radials: If you can't do dense and quarter wave, don't do
>> on-ground or buried. I realize that creating such can be beyond
>> reach, but less than the full monty on ground based radials is far
>> lossier than most realize. If that's all you can do, you're stuck
>> with it, and you will be victimized by the dirt, high losses when the
>> SWR is good and broad, and lower losses when the SWR is poor (and
>> matching is difficult).
> Ouch- then why does the SWR go from 1:1 to 5:1 with the added radials
> exposing the impedance mismatch?  I have used above and buried radials- it
> is true that until this antenna, the above ground radials always showed more
> antenna efficieny improvement issues than buried- with dogs and a small yard
> now, we bury everything-
>>
>> Solving your SWR will not solve your performance. Solve the ground
>> and then match that.
> I disagree here- Seeing the higher SWR with the added radials, shows the
> antenna becoming more efficient-  using the UnUn to lower the minimum SWR at
> resonance gives the antenna a broader bandwidth- my 2 cents (-:
>
>>
>> 73, Guy.
>>
>> On Mon, Jul 18, 2011 at 8:31 PM, BRYON PAUL n0ah VEAL <bryonveal at msn.com>
>> wrote:
>> >
>> > On my Cushcraft MA160V, the resonant SWR point has lowered from almost
>> > 5:1  to 1:1 without the Amidon unUn in line.  All 26 of the buried radials
>> > are attached.  The main difference is that the normally dry ground is
>> > saturated from 6 inches of rain in the past two weeks.  Can the water
>> > saturated soil really make this much of a difference?  The last time this
>> > antenna showed this good of an SWR, was when I had no radials attached, in
>> > dry dirt, as expected-  Of course attaching radials only began to show the
>> > true impedance mismatch, thus the need for the Amidon UnUn to match the coax
>> > to the antenna- Bottom line, the antenna is acting like I disconnected the
>> > radials, which are very much intact- My guess is that as the soil drys out,
>> > my SWR at sresonance will once again rise, and i will need the UnUn again
>> > for matching reasons- does this sound right>?
>> >
>> > 73  Paul  N0AH
>> >
>> >
>> >
>> >
>> > _______________________________________________
>> > UR RST IS ... ... ..9 QSB QSB - hw? BK
>> >
>