[OZAPRS] On possibilities with short HF whips

Ian Bennett ibennett at tpg.com.au
Fri Dec 8 18:32:37 AEDT 2017


I remember back in the 80's when I was in uniform and in Brisbane, a radio vehicle drove over the 
railway line near Enoggera with the HF whip still up. Made a BIG flash (apparently), blew a tyre, 
shutdown the train network for an hour or so and welded the 106 to it's mount.
I have two HF whips mounted on the bullbar of my 100 Series; my home made APRS antenna is just shy 
of 2m long (that was the length of the donor antenna that I dismantled) and is 3150(ish) mm floor to 
tip. I haven't had any dramas like the one mentioned above however I tie them back when negotiating 
"tight" spaces.
Will be a different story when we get our truck based motorhome but I have a cunning plan for that ;-)

Ian

On 08/12/17 17:39, Mathew McKernan wrote:
> I did similar with a Codan autotune on my Landcruiser, mounted above the spare wheel carrier 
> connected to my Codan 9323.
> 
> 
> Hit the line at the same spot... was waiting for smoke to fill the cabin. I was pleased it didn't, 
> but disappointed as it would have been pretty impressive!
> 
> ----------------------------------------------------------------------------------------------------
> *From:* OZAPRS <ozaprs-bounces at aprs.net.au> on behalf of Glen English VK1XX 
> <glenlist at pacificmedia.com.au>
> *Sent:* Friday, 8 December 2017 5:26:29 PM
> *To:* ozaprs at aprs.net.au
> *Subject:* Re: [OZAPRS] On possibilities with short HF whips
> what are the recommendations and user practical limits for Melbourne ?
> (trams)
> 
> Canberra here you'll  get into trouble ~ 4m
> 
> I had the loop on my vehicle when I was driving in Melbourne a fair bit....
> 
> I once hit a tram line with my car roof antenna heatshrink insulated
> helical at Racecourse Road, Kensington... it made a huge pop in the
> receiver but otherwise no damage...
> 
> 
> 
> 
> On 8/12/2017 3:07 PM, Matthew Cook wrote:
>> This is also worth considering when looking at larger HF whips.
>>
>> http://www.rms.nsw.gov.au/business-industry/heavy-vehicles/road-access/restricted-access-vehicles/4-6m-high.html
>>
>> Each state has their own variations to the above, nationally 
>> un-restricted is 4.3m.
>>
>> 73
>>
>> Matthew
>> VK5ZM
>>
>> On 8 December 2017 at 14:03, Graeme <graeme at abrona.com.au 
>> <mailto:graeme at abrona.com.au>> wrote:
>>
>>     Thanks Glen.
>>
>>     Obviously my decision against buying a 2.2m centre loaded 40m whip
>>     because it would bend in the wind to its disadvantage in favour of
>>     a base loaded 1.4m whip wasn't a good one for multiple reasons.
>>
>>     Graeme 2HFG
>>
>>     -----Original Message----- From: Glen English VK1XX
>>     Sent: Friday, December 8, 2017 10:19 AM
>>     To: ozaprs at aprs.net.au <mailto:ozaprs at aprs.net.au>
>>     Subject: Re: [OZAPRS] On possibilities with short HF whips
>>
>>
>>     Ran some NR predictions for 10 MHz for Brisbane Sydney, and 7 and 3.5
>>
>>     and also some more details calcs on the Diamond 1.4m logn base
>>     loaded whip
>>
>>     turns out to be ~ 3% efficiency.
>>
>>     for the -15dBi TX terminal (1.4m base loaded whip with suboptimal
>>     loading Q)
>>
>>     yep,  in daytime, single hop 750-1200km , 100W into the antenna,
>>     expect
>>     around 15dB SNR for the 300 baud modem given a good receiver
>>     antenna and
>>     setup...with a modem like DireWolf that can cope with frequency
>>     variations. Be sure you know your radio frequency offset before
>>     you start.
>>
>>     with same length whip on 7 MHz, expect about 300-700km in
>>     daylight, but
>>     not much use outside that time and distance.
>>
>>     All of this means is for 300 baud FSK packet mode and 100W, the
>>     mode is
>>     unsuitable for low efficiency mobile antennas like base loaded short
>>     whips. (3% or less efficiency at 10 MHz, 2% at 7 MHz etc)
>>
>>     All this points to: (in my opinion) needing  a >=2.2m long whip
>>     instead
>>     of a 1.4m long whip.
>>     and  an antenna with a non base loaded structure (for 300 baud packet)
>>
>>     Get your antenna efficiency up to 10% at 7 MHz and then now you
>>     have an
>>     idea setup 24 hours, single freq .... 10 MHz almost good enough except
>>     for the wee hours 2am-sunrise when you will be asleep anyway.
>>
>>     So the lesson here, 300 baud packet needs decent antenna efficiencies
>>     mobile.
>>     hence the need for a mode that does about 6dB better
>>
>>     sure we can do alot better than 6dB, but 6dB better mode is what is
>>     required to work on the 1.4m base loaded whips.
>>
>>     Otherwise for 300 baud FSk packet, it needs to be teamed up with
>>     antenna
>>     efficiency >= 8%, implying  something with a feedpoint of around 2
>>     ohms
>>     Rr and not too lossy loading and matching... a whip of 2 meters
>>     tall  at
>>     10 MHz with continuous or 1/3 loaded structure. Base loaded structures
>>     are the worst !
>>
>>     The longer 1.8m long CB helical whips are a bit hard to find these
>>     days.
>>
>>
>>
>>
>>
>>
>>
>>
>>     g
>>
>>
>>     On 7/12/2017 6:36 PM, Glen English VK1XX wrote:
>>
>>         ok
>>
>>
>>         On 7/12/2017 6:24 PM, vk4tec at tech-software.net
>>         <mailto:vk4tec at tech-software.net> wrote:
>>
>>             You are not telling me anything new
>>
>>             -----Original Message-----
>>             From: OZAPRS [mailto:ozaprs-bounces at aprs.net.au
>>             <mailto:ozaprs-bounces at aprs.net.au>] On Behalf Of Glen
>>             English VK1XX
>>             Sent: Thursday, 7 December 2017 5:10 PM
>>             To: ozaprs at aprs.net.au <mailto:ozaprs at aprs.net.au>
>>             Subject: Re: [OZAPRS] Hf gates CD
>>
>>             base station 700-1500km away will hear you, but you wont
>>             hear a station 50km away.
>>
>>
>>             On 7/12/2017 5:57 PM, vk4tec at tech-software.net
>>             <mailto:vk4tec at tech-software.net> wrote:
>>
>>                 Go for a walk
>>
>>                 -----Original Message-----
>>                 From: OZAPRS [mailto:ozaprs-bounces at aprs.net.au
>>                 <mailto:ozaprs-bounces at aprs.net.au>] On Behalf Of Glen
>>                 English VK1XX
>>                 Sent: Thursday, 7 December 2017 4:55 PM
>>                 To: ozaprs at aprs.net.au <mailto:ozaprs at aprs.net.au>
>>                 Subject: Re: [OZAPRS] Hf gates CD
>>
>>                 tracker might well have CD but:
>>
>>                 1) Consider that in the mobile, you wont hear any
>>                 stations less than the skip distance (unless they are
>>                 10km away) . The daytime skip distance might be
>>                 700km.... so anyone inside that distance you wont
>>                 hear  cause the ionosphere wont support it..it wont
>>                 support any angles higher than perhaps 45 degrees.
>>
>>                 The base station though will hear lots of
>>                 transmissions from lots of stations >700km  to 1500km
>>                 away, so there would be significant collision chance
>>                 if the position update is too often. Maybe 10 minutes
>>                 might be suitable. I dunno why people run..
>>
>>                 2) With a 5%  to 10%  efficiency mobile you wont hear
>>                 too much unless the propagation is optimal...
>>
>>
>>                 glen
>>
>>
>>
>>
>>
>>                 On 7/12/2017 5:41 PM, vk4tec at tech-software.net
>>                 <mailto:vk4tec at tech-software.net> wrote:
>>
>>                     Blind ?
>>
>>                     Tracker has CD
>>
>>                     -----Original Message-----
>>                     From: OZAPRS [mailto:ozaprs-bounces at aprs.net.au
>>                     <mailto:ozaprs-bounces at aprs.net.au>] On Behalf Of
>>                     Glen English VK1XX
>>                     Sent: Thursday, 7 December 2017 2:46 PM
>>                     To: ozaprs at aprs.net.au <mailto:ozaprs at aprs.net.au>
>>                     Subject: Re: [OZAPRS] Hf gates
>>
>>                     but how does this matter?
>>
>>                     You will  be transmitting on a frequency blind
>>
>>                     there will be receivers you cannot control
>>
>>                     There will be any number of propagation modes you
>>                     cannot control...
>>
>>
>>
>>                     On 7/12/2017 3:34 PM, Andrew Rich wrote:
>>
>>                         Hi
>>
>>                         Can I get a list of hf gates on 10.147
>>
>>                         In my planning for the Xmas run
>>
>>                         Cheers
>>
>>                     _______________________________________________
>>                     OZAPRS mailing list
>>                     OZAPRS at aprs.net.au <mailto:OZAPRS at aprs.net.au>
>>                     http://lists.aprs.net.au/mailman/listinfo/ozaprs
>>                     <http://lists.aprs.net.au/mailman/listinfo/ozaprs>
>>
>>                     _______________________________________________
>>                     OZAPRS mailing list
>>                     OZAPRS at aprs.net.au <mailto:OZAPRS at aprs.net.au>
>>                     http://lists.aprs.net.au/mailman/listinfo/ozaprs
>>                     <http://lists.aprs.net.au/mailman/listinfo/ozaprs>
>>
>>                 _______________________________________________
>>                 OZAPRS mailing list
>>                 OZAPRS at aprs.net.au <mailto:OZAPRS at aprs.net.au>
>>                 http://lists.aprs.net.au/mailman/listinfo/ozaprs
>>                 <http://lists.aprs.net.au/mailman/listinfo/ozaprs>
>>
>>                 _______________________________________________
>>                 OZAPRS mailing list
>>                 OZAPRS at aprs.net.au <mailto:OZAPRS at aprs.net.au>
>>                 http://lists.aprs.net.au/mailman/listinfo/ozaprs
>>                 <http://lists.aprs.net.au/mailman/listinfo/ozaprs>
>>
>>
>>             _______________________________________________
>>             OZAPRS mailing list
>>             OZAPRS at aprs.net.au <mailto:OZAPRS at aprs.net.au>
>>             http://lists.aprs.net.au/mailman/listinfo/ozaprs
>>             <http://lists.aprs.net.au/mailman/listinfo/ozaprs>
>>
>>             _______________________________________________
>>             OZAPRS mailing list
>>             OZAPRS at aprs.net.au <mailto:OZAPRS at aprs.net.au>
>>             http://lists.aprs.net.au/mailman/listinfo/ozaprs
>>             <http://lists.aprs.net.au/mailman/listinfo/ozaprs>
>>
>>
>>
>>         _______________________________________________
>>         OZAPRS mailing list
>>         OZAPRS at aprs.net.au <mailto:OZAPRS at aprs.net.au>
>>         http://lists.aprs.net.au/mailman/listinfo/ozaprs
>>         <http://lists.aprs.net.au/mailman/listinfo/ozaprs>
>>
>>
>>
>>     _______________________________________________
>>     OZAPRS mailing list
>>     OZAPRS at aprs.net.au <mailto:OZAPRS at aprs.net.au>
>>     http://lists.aprs.net.au/mailman/listinfo/ozaprs
>>     <http://lists.aprs.net.au/mailman/listinfo/ozaprs>
>>     _______________________________________________
>>     OZAPRS mailing list
>>     OZAPRS at aprs.net.au <mailto:OZAPRS at aprs.net.au>
>>     http://lists.aprs.net.au/mailman/listinfo/ozaprs
>>     <http://lists.aprs.net.au/mailman/listinfo/ozaprs>
>>
>>
>>
>>
>> _______________________________________________
>> OZAPRS mailing list
>> OZAPRS at aprs.net.au
>> http://lists.aprs.net.au/mailman/listinfo/ozaprs
> 
> 
> _______________________________________________
> OZAPRS mailing list
> OZAPRS at aprs.net.au
> http://lists.aprs.net.au/mailman/listinfo/ozaprs
> 
> 
> _______________________________________________
> OZAPRS mailing list
> OZAPRS at aprs.net.au
> http://lists.aprs.net.au/mailman/listinfo/ozaprs
> 


More information about the OZAPRS mailing list