[OZAPRS] Newb HF questions ;)
Terry Neumann
tfneumann at internode.on.net
Wed May 20 09:56:48 EST 2009
G'day Damien,
Yep - try that - experiment around and see what works. You may not get
there on all bands, but get one working first.
I'm off to Adelaide for the day as VK5ATN-9. Good luck , success is
guaranteed, you just have to get the right combination :-) .
73
Terry
Damien Gardner Jnr wrote:
> Hey Terry,
>
> Cheers, will pull the balun out, and see how it goes - I was 99% sure
> it was just a really bad idea on a vertical, but lee @ andrews was
> pretty adamant it was needed, and I figured he's been in the business
> a long time so knew what he was talking about.. I'll make sure to
> ask an actual ham next time I go buying gear ;)
>
> Re 'pretty darned close to 50 ohms', that was from ray's workings
> earlier showing it was 40 ohms on 30m - I figured that's a hell of a
> lot better than the 10ohms being presented to the ATU at the moment ;)
>
> Cheers,
>
> Damien
>
> On 20/05/2009, at 9:11 AM, Terry Neumann wrote:
>
>> Damien Gardner Jnr wrote:
>>
>>> Hey Norm
>>>
>>> I'm a little confused by the balun too ;)
>>>
>>> 50 ohms u/b from the rig to the atu
>>> atu is u/b (50 ohm?) to the PL259 on the bottom of the balun.
>>> balun balanced side has one terminal to the bottom of the TEV-1,
>>> and one side to the 'radials' terminal on the mounting plate for
>>> the TEV-1, which is bolted directly to the mast. I can see why
>>> you'd have the 4:1 balun if you were feeding a dipole, but as ray
>>> said earlier, on 30m, the TEV-1 is pretty damned close to 50 ohms,
>>> so I would have thought putting the balun in there would
>>> completely screw the vswr?? (it'd be giving me ~11 ohm on 30m yeah?)
>>
>>
>> It certainly should, and would most probably produce problems
>> similar to those you are seeing.
>> Take the balun out as a first step. The presence of the balun on
>> the TET Emtron web site is a real puzzle. It could be useful at
>> some out of the ball park frequency, but flies in the face of
>> everything one reads about the feeding of vertical antennas
>> elsewhere. If you use the balun at all, put it right at the
>> transceiver /atu and run a balanced line (300 ohm ribbon?) from
>> there to the feed point of the antenna and the ground system at that
>> point.
>>
>> The TEV-1 at a length of 8.5 metres calculates out as a quarter
>> wave vertical at approx. 8.8 Mhz. This is a very long way from any
>> amateur allocation and as such in a "ideal" ground plane antenna
>> would exhibit a feed impedance of 50 ohms only at that frequency
>> (8.8Mhz). Something is very seriously wrong if it "is pretty
>> damned close to 50 ohms" on 30 metres as is. Something else in the
>> system is doing the most of the radiating - or absorbing the RF
>> energy as heat somewhere - or both.
>>
>> 73
>> Terry
>>
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