Topband: Rohn 25 Vertical questions.

[donovanf at erols.com]

Hi Rick, 


A "magnetic" loop will provide at least a 20 dB null, that's good. But 
it doesn't provide the weak signal receiving capability of a high 
performance receiving antenna. Very small magnetic loops provide a 
25 dB null but at the expense of much worse weak signal performance. 
Like so many things with antennas, there's no free lunch... 


SDRs are excellent receivers, but they have inadequate in-band dynamic 
range for the in-band receiving we're discussing in this thread. 
SDRs are not designed for extreme in-band dynamic range. 


The section joints in Rohn 25/45/55 towers are at risk of micro arcing 
because they -- intentionally -- do not fit tightly. There are multiple 
approaches to electrically bond the sections. 


There's a big difference between a vertical -- or any antenna -- that 
"works" and one that is specifically constructed so it cannot micro-arc. 


73 
Frank 
W3LPL 

----- Original Message -----

From: "Richard (Rick) Karlquist" <richard at karlquist.com> 
To: donovanf at erols.com, "Ron WV4P" <wv4ptn at gmail.com> 
Cc: "160" <topband at contesting.com>, "Mail 10" <mail10 at barefoothorse.com.au> 
Sent: Thursday, August 20, 2020 10:17:29 PM 
Subject: Re: Topband: Rohn 25 Vertical questions. 



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