WICEN Vic: WICEN 80m Net 29 June 2012

Sun Jul 4 20:14:34 CDT 2021

Hi Peter & everyone

Re the whip, short HF whips is a whole topic in itself!   Yours sounds 
like it is in an almost ideal situation.

If anyone is interested, I've attached a spreadsheet (Excel, LibreOffice 
Calc) for calculating the required loading coil inductance for a short 
(less than 1/4 wave) whip.  It's based on a method published in Ham 
Radio magazine many years ago.

The spreadsheet can be used with base loading, centre loading, or 
combined base + centre loading.  The last is useful for a portable 
antenna where (for efficiency) you want most of the loading somewhere in 
the middle of the whip but (for frequency agility) you want to be able 
to tune the antenna near ground level using a tapped coil.

The spreadsheet greatly reduces the amount of "cut and try", and you can 
check out design choices before you build the antenna.  It deliberately 
slightly over-estimates the inductance, it is much easier to remove coil 
turns than add them!

Instructions on how to use the spreadsheet are included in the spreadsheet.

All the inductor does is tune the whip to resonance.  It does not bring 
the feedpoint impedance to 50 ohms.  A good (efficient) 80 m mobile whip 
should have a feedpoint impedance of only a few ohms at resonance and 
will also require a matching system to match to 50 ohms.  This can be a 
matching transformer or one of a variety of matching networks. This is 
one situation where SWR can be misleading - without a matching system, a 
good 80m mobile whip has much higher SWR than a poor one!   Tuning and 
matching are not the same thing.

For any short antenna, generally the longer the better. Radiation 
resistance is roughly proportional to the square of whip length.  If 
other losses stay about the same (and the dominant loss is ground 
losses) then efficiency is also roughly proportional to the length 
squared.  Double the length = 4x the radiated signal.  It is instructive 
to try putting a few length values into the spreadsheet and see what 
happens to the radiation resistance.

Why is efficiency so important for a HF whip?  Efficiencies of a typical 
80m whip range from abysmal (eg a popular multitapped whip at very much 
less than 1%) to poor (even a very good 80m whip will only be a few 
percent efficient).

Just to illustrate this point, I have measured more than 20 dB 
difference in radiated signal between a reasonable 80m whip and a poor 
one.  That's over 3 'S' points.  The measurement was done with 
calibrated equipment.

Many operators are misled about whip performance by the apparent ability 
to hear other stations on receive.  On 80m, where the receiver noise 
floor is way below band noise, even a 20dB reduction in signal strength 
goes largely un-noticed on receive but is very noticeable at the far end 
on transmit.  So the ability to hear stations on a mobile whip is not a 
good indicator of whip performance.

Anyway, hope the spreadsheet is useful and gives some insight into how 
short whips behave.

Cheers,   John VK3ZRX

On 04/07/2021 23:02, Peter Weeks Radio wrote:
> Hi Everyone,
>
> Thanks for the signal strength comparison chart John,  it certainly 
> saved me looking it up.
>
> The antenna is mounted mid roof of my workshop roof being 20m x 24m x 
> 6m high and work much better with extended whip on 160, 80 & 40
>
> Regards
> Peter
> VK3YZP
>
> Sent from my Phone
>
>
>
>> On 3 Jul 2021, at 19:44, John & Bronwyn <jandbmorrissey at gmail.com> wrote:
>>
>> 
>>
>> Net opened at 20:30 hrs on 3600 kHz with VK3ZRX as Net Control.
>>
>> Checkins:
>>
>> Mark VK3MDH  /P Cobram, 59, reports lots of Vicpol activity along the 
>> NSW / Vic border to do with Covid bans on people entering Vic from 
>> any NSW 'red spot'.
>>
>> Paul VK3FPDA, 57, reported poor sigs from everyone
>>
>> Rik VK3EQ,  58, check in only,
>>
>> John VK3MS Milawa, 59, working on getting his shack set up & functional
>>
>> Peter VK3YG Glenmaggie, 59, going interstate for a few days, also 
>> celebrating 57th wedding anniversary.  Congrats Peter and Jen!
>>
>> Peter VK3YZP Alexandra, 58, using a Codan radio with tunable vertical 
>> (a Codan screwdriver with extended whip), reported my sig as +14dBuV 
>> (see below)
>>
>> All greatly saddened to hear of the passing of long-term WICEN member 
>> Fred VK3JM.  Vale Fred.
>>
>> Coming events:
>>
>> Saturday August 7th 2021
>> Gippsland Rally
>> Heyfield area
>> Contact: Ross Sargent VK3SF phone: 03 9736 4020
>> Email:vk3sf at outereast.com.au
>>
>> Sunday August 15th 2021
>> Commanders & Co-Ordinators Meeting
>> ZOOM (TBC )
>> Contact: Ross Sargent VK3SF phone: 03 9736 4020
>> Email:vk3sf at outereast.com.au
>>
>>  Net control next week:  Paul VK3DPW
>>
>> Change of Net Control Roster:  With Fred's passing and another Net 
>> Control station not available for the foreseeable future (due to 
>> other commitments), I think it is time to revise the roster.
>>
>> Anyone interested in being added to the net control roster, please 
>> contact me.   It is an interesting role and a valuable skill to have!
>>
>>
>> And lastly, an explanation of Peter 3YZP's signal report.  The most 
>> common signal report is "S" units, with (on HF) S9 defined as 50 uV 
>> at the antenna terminals. Then each lower "S" number is half the 
>> signal strength (-6dB) of the one just higher.  Another common 
>> specification is the actual signal strength in uV, most radios are 
>> specified in this way for sensitivity. Then there is dBm, which is 
>> the signal level in dB referred to a signal level of 1 mW into 50 
>> ohms (this is about 0.224 volts).
>>
>> As well, some radios define signal levels in dB relative to 1uV, with 
>> abbreviation dBu.
>>
>>  For comparison, here are the various "signal strength" scales:
>>
>> 'S’ Units (HF) 	uV 	dBu 	dBm
>> 9 	50 	34 	-73
>> 8 	25 	28 	-79
>> 7 	13 	22 	-85
>> 6 	6.3 	16 	-91
>> 5 	3.2 	10 	-97
>> 4 	1.6 	4 	-103
>> 3 	0.8 	-2 	-109
>> 2 	0.4 	-8 	-115
>> 1 	0.2 	-14 	-121
>>
>> And just to confuse things further, there are actually two "S unit" 
>> scales.  On HF, S9 = 50 uV.  But on V/UHF, S9 = 5 uV.  This makes S1 
>> on V/UHF = -141 dBm - pretty much at the noise floor of a very good 
>> VHF/UHF receiver.  So it makes sense.  And there are two dBu scales - 
>> the one above which uses 1 uV, and another which uses 0.5 uV as the 
>> reference, which is used by some Japanese manufacturers.
>>
>> In practice the "S-unit" scales are nominal, not all manufacturers 
>> follow the "S-unit" standard and even then, radios often don't follow 
>> the scales accurately.
>>
>> So my report from Peter of +14dBu was about S6.
>>
>> Cheers,   John VK3ZRX
>>
>>
>> _______________________________________________
>> wicenvic mailing list
>> wicenvic at vic.wicen.org.au
>> http://vic.wicen.org.au/mailman/listinfo/wicenvic_vic.wicen.org.au
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