Jim,
You may have missed it, but his diagram shows his 1M ground rod directly
connected to his antenna, with no grounding for his equipment. I certainly
hope the diagram is incorrect and he is not depending upon his 2.5M coax
shield for station ground. Since the antenna is on the roof, he may be
better off connecting the ground to his station, and use raised radials for
his antenna.
Placing a bunch of ferrites on the coax feedline will go a long way to
solving the symptom, RF riding the coax, but not the underlying issue;
impedance mismatch at the feed point. The elegant way of resolving the issue
is to build a Unun to transform the feedline impedance to the antenna
impedance, interface the output of the Unun to a 1:1 Balun, and then connect
the output of the Balun to the antenna. This will resolve the impedance
mismatch and definitely cut back on the reflected RF from riding the cable
back to the shack. The only caveat with this is that you are now locked
into a mono-band antenna for the most part. Given his antenna is on a roof
with coax in the near field on its short run to the shack, I would put the
ferrites on the shack end to keep the induced RF at bay.
Your friends M2 Balun sounds like a "dirty balun" gone wrong ;-) It is not
the amount of turns that really matters, it is the length of the coax used,
and the turns have to be a consistent radius touching only the two windings
adjacent to it in order for it to work properly. Scramble winding will work
in a quick pinch, but without a form it has a tendency to fall apart over
time. If it is to be permanent, and you really want to use a dirty balun,
then you should use some kind of PVC form to wind it on.
73,
Mike
W5CUL
-----Original Message-----
From: Jim Thomson [mailto:jim.thom@telus.net]
Sent: Saturday, October 30, 2010 5:44 PM
To: W5CUL; amps@contesting.com
Subject: Re: [Amps] use or not coaxial audio cable to transmitter's
--------------------------------------------------
From: "W5CUL" <w5cul@sbcglobal.net>
Sent: Saturday, October 30, 2010 3:15 PM
To: <amps@contesting.com>
Cc: "'Jim Thomson'" <jim.thom@telus.net>
Subject: RE: [Amps] use or not coaxial audio cable to transmitter's
> Tzikas,
>
> A Balun at the antenna end and Ferrite at the shack end should help with
> RF
> riding the coax cable into the shack. Build the balun to transform the
> impedance at the antenna feed point to that of the impedance of the coax.
> I
> don't understand what is meant by "metal house", but a 2.5M coax puts the
> equipment kind of close to the antenna though. Don't know if that would
> be
> a part of the issue or not. Last observation would be 1 ground rod. May
> not
> be enough for a good RF ground, but should work great for DC. One
> question,
> how is the PLL, Amp & Power supply grounded?
>
> I think someone already mentioned a good type of audio cable to use, one
> with a braided shield and or foil wrap. I use a cable that has two
> twisted
> pairs surrounded by a very heavy braided shield for all of my audio
> connections between gear. Here is a hyper-link, maybe you will be able to
> find a distributor in your location:
>
> http://www.canare.com/ProductItemDisplay.aspx?productItemID=53
>
> 73,
>
> Mike
> W5CUL
&&&&& That 9M of grnd wire from roof to the dirt is probably causing him
more problems than
it solves. That's 31' of grnd wire , to get to grnd. Meanwhile, his
vertical ant is radiating into both the
shack, and the 31' of grnd wire as well.
&&& My buddy who had the RFI problem with his new m2 80m yagi, also has a
6m RFI problem now. The 80M
RFI problem was cleared up by installing 20 x type 43 beads slid over
coax...at the output of his HF amp. Before that,
he was knocking his dsl modem offline, and RFI from one end of the house to
the other. The m2 supplied 80m balun,
was just some rolled up coax, inside the switch box. Clearly it does not
have a high enough Z.
&& The 6M RFI problem was a doozy. Distorted audio, that gets really bad
when 6m yagi pointed over top his house.
The tower is right behind the house too. 6M coax is separate from HF
coax...and 6m coax is routed directly from 6m yagi
to the output of the dedicated 6M amp. I suggested a bare min of 10 x
type 43 beads [ he has lots of large beads in his junk box]
and he installed 23 of em, slid over RG-213, right at the output of the 6m
amp. Problem solved on 6M. No more distorted
audio, and very clean. The 6m yagi was a case of yet another m2 balun
being used, the 6m one is a short, cylinder type of thing.
All the other hf ant's used 17 x large type 43 beads slid over coax, zero
problems with all of those ant's.
&& I would suggest that Tzikas 1st try a load of ferrite at the feedpoint
of his vertical. If that doesn't completely solve the
problem, then install another load of ferrite on the output of his 500W
amp. If his Mic is generic, unbalanced type, like most stock ham gear,
then plane RG-58/59 will work just fine for a mic cable.. All you need
for the mic is hot audio and grnd.
RG-58/59 will fit the bill..and do the job nicely, and it's readily
available. If you need PTT, then use a footswitch......and use more
RG-58
from footswitch to back of xcvr. Sure, the radio comes with a 8 x pin mic
connector/cable, but who needs the up/down junk?
&&& I think the above will solve most of his problems. One other thing he
could try is to temp disconnect that 9M grnd wire. His 9M
grnd wire is longer than his 2.5 M coax to base of vertical. That 9M
long grnd wire is parallel to the vertical. My guess is the vertical is
radiating loads of RF into the 9M grnd wire..which is coming right back up,
and into the 500w amp + xcvr.
Jim VE7RF
>
> -----Original Message-----
> From: amps-bounces@contesting.com [mailto:amps-bounces@contesting.com] On
> Behalf Of Jim Thomson
> Sent: Saturday, October 30, 2010 12:20 AM
> To: amps@contesting.com
> Subject: Re: [Amps] use or not coaxial audio cable to transmitter's
>
>
> ### He posted a diagram in his 4th posting. His coax to vertical on
> roof
> is just 2.5M long.
> He also has 9 M of grnd wire from metal to the dirt. He has a xcvr +
> 500
> w amp. He probably
> requires ferrite at both the base of the vertical..and also in the
> shack....
> IE: both ends of the coax.
>
>
> http://tzitzikas.site90.net/files/installation.JPG
>
> Jim VE7RF
>
>
> On 10/29/2010 9:20 AM, tzikas tzik wrote:
>> pll= phase lock loop . This equipment keep the frequency of oscillator
>> stable
>
> Understood. But more questions.
>
> You say 500 watt transmitter. Most ham transmitters are 100W output, and
> if you want more power, you add a power amplifier. Is this a 500W
> transmitter all in one box, or two boxes?
>
> Where does this cable run? Inside the transmitter, from one point to
> another, or outside the transmitter, between boxes? What is the
> transmit frequency?
>
> What kind of cable is it? Coax or two conductors plus shield? What
> kind of shield? What kind of circuit is connected to the cable at each
> end? Balanced or unbalanced? Where is the shield connected?
>
> 73, Jim K9YC
> _______________________________________________
> Amps mailing list
> Amps@contesting.com
> http://lists.contesting.com/mailman/listinfo/amps
>
>
_______________________________________________
Amps mailing list
Amps@contesting.com
http://lists.contesting.com/mailman/listinfo/amps
|
