[OZAPRS] Need a hand

Sun Dec 3 21:19:59 AEDT 2017

Thanks Glen

Will revisit the car tomorrow

A

-----Original Message-----
From: OZAPRS [mailto:ozaprs-bounces at aprs.net.au] On Behalf Of Glen English VK1XX
Sent: Sunday, 3 December 2017 8:00 PM
To: ozaprs at aprs.net.au
Subject: Re: [OZAPRS] Need a hand

OK good stuff thanks for the answers.

1) Magbase has insufficient capacitance at 10 MHz to give you any sort of ground. I wouldnt recommend a base base below 60 MHz or so, depending on the construction and the antenna.

2) Bonnet mount good but are the screws deep into your paintwork right through to the base metal  to get a good ground? probably not.

suggest take a earth wire off the baseof the magbase body or the bonnet mount to a chassis  or panel bolt, this probably means relocating the antenna, maybe. if onto the bonnet you might want to connect to the bonnet and then connect the bonnet to a bolt in the engine bay to ground that panel (rather than the hinges) . some vehicles have ground straps for that.  the wire to the immediate ground should be a good choice for the RF compared to the coax , so maybe something at least 2.5mm2 or flat strap and less than a meter long.

you'll need to re evaluate the antenna location/ mountaing to get a suitable immediate ground connection for the antenna (as the ground is half of the antenna, without it, the antenna wont feed)

On 3/12/2017 8:22 PM, Andrew Rich wrote:
> Both a bonnet mount and maggy mount in center of roof
>
> Diamond 30 meter vertical
>
> Radio is only connected via cigarette lighter
>
> Getting 6:1 and 9:1
>
> Vna dips but vswr is 6:1
>
> Might try my vhf whip on vna
>
> Not sure car and antenna base are grounded
>
> Like something is floating
>
> I need to measure ohms to chassis
>
> Rg58 only 4 Meters
>
> Radio ground only by power lead
>
> Vna is floating
>
> Not tried any ground straps yet
>
> A
>
>
> Sent from my iPhon
>
>> On 3 Dec 2017, at 5:56 pm, Glen English VK1XX <glenlist at pacificmedia.com.au> wrote:
>>
>> hi Andrew
>>
>> Please do ya best to answer the following barrage of questions and I may be able to assist :
>>
>> but all questions need to be answered to solve the crossword...
>>
>> 1) what is the whip.
>>
>> 2) where is it located, precisely
>>
>> 3) does the ground on the base of the whi[ measure 0 ohms to the chassis ?
>>
>> 4) how long RG58 lead in ?
>>
>> 5) Is the radio grounded via a local ground short strap/thick wire to earth bolt or only its negative power lead ?
>>
>> 6) does it dip below 2:1 VSWR anywhere when you sweep it with a VNA ?
>>
>> 7) With the VNA, is the VNA grounded, or floating on the end of the  coax?
>>
>> 8) With the VNA, if floating, does the VNA indicated sweep/match 
>> change if you ground the outer of the VNA coax connector to a local 
>> ground like ground bolt ona  door hinge etc
>>
>>
>>
>>
>>> On 3/12/2017 6:42 PM, Andrew Rich wrote:
>>> I bought a 30 m whip for the car
>>>
>>> Can’t get better than vswr 6:1
>>>
>>> I was told I need to ground the base
>>>
>>> Also cigarette lighter maybe not enough current ?
>>>
>>> 10.147 MHz
>>>
>>> Andrew
>>>
>>> Sent from my iPhone
>>> _______________________________________________
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>>> OZAPRS at aprs.net.au
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>>
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