[OZAPRS] Grounding of HF Antenna for APRS

[Matthew Cook]

Glen,

This will be useful for anyone wishing to set up 30m/40m APRS, I see no
reason to move it off list.

73

Matthew
VK5ZM

On 4 December 2017 at 12:11, Glen English VK1XX <
glenlist at pacificmedia.com.au> wrote:

> BTW everyone, if this is too off topic I can carry this privately. I have
> experience with MF/LF antennas.....
>
> HF30FX ahh yeah , right previous generation base loaded compared to the
> centre loaded ones
>
> yes, very much ground dependent. anything under 2:1 is probably OK, with
> various ground arrangements see if there is a pronounced dip anywhere
>
> the sharper the dip, the more likely the efficiency is good .
>
> My approach would be to ginore the VSWR once below 2:1 and try and get the
> sharpest looking VSWR versus frequency curve
>
> think of it this way :
>
> If it was a dummy load, it would be good at all frequencies
>
> if it was a high Q tuned circuit, then it would be good VSWR at only one
> freq and infinite everywhere else
>
> Your antenna will be somewhere in between a dummy load and a pure tuned
> circuit...probably about 2:1 SWR BW of 50kHz (assume centre matched to
> 1:1)  indicates reasonable efficiency.
>
>
>
>
>
> On 4/12/2017 12:13 PM, vk4tec at tech-software.net wrote:
>
>> Diamond HF30FX
>>
>>
>>
>> -----Original Message-----
>> From: OZAPRS [mailto:ozaprs-bounces at aprs.net.au] On Behalf Of Glen
>> English VK1XX
>> Sent: Monday, 4 December 2017 11:09 AM
>> To: ozaprs at aprs.net.au
>> Subject: Re: [OZAPRS] Grounding of HF Antenna for APRS
>>
>> well, there are alot of assumptions for pre cut antennas on vehicles for
>> HF.
>>
>> So I wouldnt pay too much attention to SWR once it is below 2:1. What
>> sort is it ? WHat model / URL ?
>>
>>
>> On 4/12/2017 11:58 AM, vk4tec at tech-software.net wrote:
>>
>>> I went to see an engineer mate
>>>
>>> He gave me some brass plate
>>>
>>> I am cutting out a plate that will have a braid strap coming off it
>>>
>>> That should do the trick - he said the VSWR should come down even further
>>>
>>> Nudge bars are $1000
>>>
>>> Andrew
>>>
>>> -----Original Message-----
>>> From: OZAPRS [mailto:ozaprs-bounces at aprs.net.au] On Behalf Of Glen
>>> English VK1XX
>>> Sent: Monday, 4 December 2017 7:35 AM
>>> To: ozaprs at aprs.net.au
>>> Subject: Re: [OZAPRS] Need a hand
>>>
>>> yeah that will work. it would be out of the weather, and get covered
>>> with oil/grease and probably weather seal it.
>>>
>>> being close to the feedpoint actually isnt that necessary, maybe no more
>>> than 1/20 of a wavelength, though , that is probably a good number. so max
>>> strap length 1.5m for that freq.
>>>
>>>
>>> On 4/12/2017 8:27 AM, vk4tec at tech-software.net wrote:
>>>
>>>> Glen
>>>>
>>>> I am thinking that maybe just a strap that fits in the gap between the
>>>> bonnet and the side wall.
>>>>
>>>> I can sink a screw into the bonnet just inside
>>>>
>>>> That way it would be as close to the feed point as possible
>>>>
>>>> I would drill into the top side of the bonnet but that equals a
>>>> divorce LOL
>>>>
>>>> -----Original Message-----
>>>> From: OZAPRS [mailto:ozaprs-bounces at aprs.net.au] On Behalf Of Glen
>>>> English VK1XX
>>>> Sent: Monday, 4 December 2017 7:23 AM
>>>> To: ozaprs at aprs.net.au
>>>> Subject: Re: [OZAPRS] Need a hand
>>>>
>>>> In looking for a place to attach a ground strap, consider that ideally,
>>>> you want the largest continous area of metal. That is probably the engine
>>>> bay firewall (which would attach to the upper body, roof etc) , fender
>>>> mounts,  or in the rear, hinge mounts of the rear hatch, etc.
>>>>
>>>> Anyone else have any input here  on where to connect on a modern
>>>> vehicle to maximise surface area ?
>>>>
>>>> comeon. ???
>>>>
>>>> I am a bit out of tough on modern vehicles. (I have a 2005 XC90 which
>>>> if you pass a RG58 through a door seal will squash it flat and cause a
>>>> short... hence requiring coax entry through a bung in the spare tyre
>>>> well under the vehicle)
>>>>
>>>>
>>>>
>>>>
>>>>
>>>>
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>>
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>
>
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