Topband: antenna analyzers

[Jeff Blaine]

At this location, the VNWA is a bit squirly near the BC band but with a 
single L/C notch added at the device input (within the cal plane), it 
works fine.

The AA-55 Zoom I have is immune and is the my go-to instrument for field 
work.  Recommended.

MFJ-259 is too easily disturbed and is not reliable with any antenna of 
larger physical size.

5KW BC station about 5 miles east of here.

73/jeff/ac0c
alpha-charlie-zero-charlie
www.ac0c.com

On 12-Oct-18 3:35 PM, Wes Stewart wrote:
> I can vouch for the AA-55 Zoom, although it is not without flaws. I 
> live 5.9 miles from a 50KW BC station on 1550 kHz.  On my 160-meter 
> inverted-L they are 70 dB over S9 on a calibrated K3, that's 70 dB 
> above -73 dBm or -3dBm. As long as I don't sweep through that 
> frequency, the analyzer is unfazed.  As an aside, I have yet to find a 
> low cost SDR that will stand up to this.  I had to return a RSP2 Pro 
> that even with BC band filtering folded up like a cheap suitcase.
>
> My N2PK VNA works fine as does the DG8SAQ VNWA.  I just last night 
> finished building a DG5MK designed FA-VA5, which I suspect will do 
> okay.  It will run using the VNWA software too.  Good thing, since so 
> far, the standalone interface is wanting, but that could be my 
> failing.  (It's really tough to run an instrument this powerful with 
> just three push buttons)
>
> Note that all of these are vector analyzers.
>
> Wes  N7WS
>
> On 10/12/2018 12:20 PM, Richard (Rick) Karlquist wrote:
>>
>>
>> On 10/12/2018 12:02 PM, AC0RL via Topband wrote:
>>
>>> I have found that antenna analyzers can get screwed up on long 
>>> antennas if
>>> there are nearby transmitters; AM stations or any other transmitter 
>>> that can
>>> swamp out the input to the analyzer. I live 1/4 mile from a 1kw am 
>>> station
>>> and I cannot use any brand of analyzer on the HF bands. I must use a 
>>> SWR
>>> bridge and a transmitter.
>>>
>>> Jerry Kahn
>>> AC0RL
>>
>> Don't lose hope!
>>
>> I live 6 miles from a 50 kW BCB station.  Most analyzers are useless.
>> Then I bought the Rig Expert AA-55 zoom.  All I can say is:  it works
>> flawlessly at this QTH on a 90 foot top loaded vertical.  Also, the
>> AA-55 can be protected with a BCB reject filter, which can then be
>> calibrated out.  If you play that card, I'm sure you will be OK even
>> at your high QRM QTH.
>>
>> You can also use an N8LP digital wattmeter which reads out impedance,
>> not just SWR.  Larry tells me that you have to locate the device's
>> coupler at the antenna (not in the shack) and the cables between
>> the coupler and main box cannot exceed 20 feet.  With those caveats,
>> this is a bulletproof way to make R + jX measurements.
>>
>> A poor man's retro solution is to build a noise bridge for 160 meters.
>> AFAIK, no commercially made bridge works on topband.  You can take
>> a published design for the higher bands and just extrapolate it to
>> 160, by replacing the variable capacitor with a triple 365 pF broadcast
>> receiver unit.  You might have to increase the amount of ferrite
>> in the bridge transformer.
>>
>> Rick N6RK
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