Topband: Rohn 25 Vertical questions.

[Jim Brown]

As always, great advice from George, Frank, Rick, and Tim. I will add 
that for all issues of crosstalk and other forms of EMI, BONDING is at 
least as critical as shielding, and that Mother Earth is not a sump into 
which those problems are poured. Also, all old hands at this biz have 
emphasized that bad shield connections on coax and other coax shield 
faults are a common weak point. And that very low resistance coax 
shields (RG400, for example) reduce transfer impedance by as much as 20 
dB, and choking RX antennas to minimize shield current that excites it.

Wish me well -- I'm evac from fires, and don't know if I still have a 
station. K6XX fears that his is gone.

73, Jim K9YC

On 8/21/2020 12:27 PM, GEORGE WALLNER wrote:
> At C6AGU I have in-band RX on all bands. The rigs are Flex 6000 SDR-s. 
> On 160 m I can hear virtually unimpaired to about 12 kHz off the TX 
> frequency. RX antenna is 4 direction delta loop, about 1000' from the TX 
> vertical. The RX path includes a high performance RX pre-amp. (The RX 
> antenna "gain" is -32 dBi.)
> SDR-s can work for in-band RX, but you must have a very "clean" RX (and 
> TX) paths and plenty of antenna separation. Also, lots of shielding and 
> grounding.
> 
> 73,
> George,
> AA7JV/C6AGU
> 
> 
> On Thu, 20 Aug 2020 15:17:29 -0700
>   "Richard (Rick) Karlquist" <richard at karlquist.com> wrote:
>>
>>
>> On 8/19/2020 10:28 PM, donovanf at erols.com wrote:
>>> Hi Ron,
>>>
>>>
>>> 700-1200 foot spacing should provide good in-band receiving capability.
>>> SDR receivers won't work for in-band receive, you must use a traditional
>>> transceiver such as the K3, K4HD, FTdx5000, IC-7800 etc.
>>>
>>>
>>> Micro-arcing is caused by transmitted RF jumping a spark gap.
>>> Any metal-to-metal joint that isn't securely bonded is a candidate
>>> for micro-arcing.
>>>
>>>
>>> 73
>>> Frank
>>> W3LPL
>>>
>> Three questions:
>>
>> 1.  Does "in-band receiving" mean the same thing as SO2R in a single
>> band contest?  I operated a few 160 meter contests in that mode around
>> 10 years ago.  I used a carefully nulled receiving loop 1000 ft from the
>> TX vertical.
>>
>> 2.  Please explain the comment about SDR receivers not working.  I
>> now have a Flex 6700 that claims to be able to do full duplex.  And
>> that radio would not work?
>>
>> 3.  If connections between R25 sections cannot be trusted, then
>> how would any crank up tower possibly work as a vertical?  I have
>> always wondered about this.
>>
>> BTW, cellular sites have significant problems with what they
>> call "passive IMD", of which micro-arcing is a subset.
>>
>> 73
>> Rick N6RK
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