Diamond CP6 - the saga continues.
Conor
interesting observation has come to light.
Yesterday, I decided to ground the co-ax feeding it where it comes into
the house. I stripped the outer insulation off the RG213 and used 1"
wide flat braid between it and a 6ft ground rod. On 40m, it is centered
on 7.130. Prior to doing this, SWR used to rise to just short of 3:1 at
7.2MHz and go off the scale below 7.07MHz. Since doing this, SWR at the
bottom end of the 40m band now mirrors that at the upper, meaning I have
full coverage of the entire 40m band below 3:1 SWR. Why it has become
more broadband, I don't know. It could be rig specific, especially as
when putting a choke loop in as Diamond recommend, my FT-950 becomes
very unhappy with it whereas my TS-480 couldn't care less. Not tried the
TS-480 on it with the grounding.
Next stage in the farce is to swap out the 3m aluminium pole its
attached to to a 5m one which is roughly the same length as the antenna.
In addition, I'll also add additional RF grounding at the base of the pole.
It'll be interesting to see what effect that has.
Ultimately, it'll still be a crap antenna but at least it's given me
something to fill the time for a couple of days.
--
Conor I'm not prejudiced. I hate everyone equally.
David
Conor
There are a number of web sites dealing with this antenna and problems.
No time to look now but will send links tonight when I get home.
Will e-mail direct as by that time this thread will have degenerated
Dave
Chris Street
Have you a proper anaylser on this - can you see the feedpoint
impedance? I'm just wondering if the feeder is also radiating - have
you a choke balun near the antenna and does that make a difference?
Conor
Thanks Dave. Address is valid.
Spike
Conor wrote:
Sounds like you've got currents on the outside of the feeder, implying
some form of mismatch even though the SWR itself might look OK.
Clearly, different rigs handle this in different ways, some better
than others.
Keep in mind that there are two incompatible things here: bandwidth
and efficiency.
A broadband antenna is inefficient, while an efficient antenna (even
at HF) might only work over a very narrow band of frequencies indeed.
Just to confuse things, some HF antennas do the latter while being
inefficient, e.g. short loaded whips.
Welcome to the wacky world of antenna experimentation.
Aero Spike
--
Not a member of the RSGB since 1959
One's straighter talk is drowned yet unsurpassed
dBs, tune-ups, banana plugs, heat-bands: all B-classed
Conor
> Have you a proper anaylser on this - can you see the feedpoint
> impedance? I'm just wondering if the feeder is also radiating - have
> you a choke balun near the antenna and does that make a difference?
>
No. I have a MFJ analyser and it doesn't play with it at all but
apparently that's a known issue, possibly due to the fact both the
center and braid side of the SO239 are connected to the vertical and
radials however that may only be a DC only connection.
I'm sharing the same thoughts as you about the feeder radiating. The
only choke its had in is an airwound one with similar results to the
loop. However, its strange that the FT-950 has issues with one inline
but the TS-480 doesn't. Might be time to break out a flourescent tube
and see what lights up.
I'm wondering if there's an Unun in the matching section. It is quite
specific how this should be bolted to the supporting pole. Without
cutting it to bits, its hard to find out what's going on. Hopefully in
the links Dave sends me, there may be the answer.
Gareth Evans G4SDW
news:42j5u5pnurrbbdk5j...@4ax.com...
> Welcome to the wacky world of antenna experimentation.
Mrs.Nugatory realises at last what the rest of us have realised
for years about her world!
Conor
> Sounds like you've got currents on the outside of the feeder, implying
> some form of mismatch even though the SWR itself might look OK.
It would be why the instructions say to put a choke loop in then.
> Clearly, different rigs handle this in different ways, some better
> than others.
>
> Keep in mind that there are two incompatible things here: bandwidth
> and efficiency.
>
> A broadband antenna is inefficient, while an efficient antenna (even
> at HF) might only work over a very narrow band of frequencies indeed.
>
Sadly, this appears to be neither. I run a Tarheel on the car and its
many times better.
> Just to confuse things, some HF antennas do the latter while being
> inefficient, e.g. short loaded whips.
>
> Welcome to the wacky world of antenna experimentation.
>
Heh-heh. Could be worse - I could've paid �300 for it.
Jim GM4DHJ in the Radio Shack ...
> Ultimately, it'll still be a crap antenna but at least it's given me
> something to fill the time for a couple of days.
>
that's nice ...
David
Those links I sent were for the wrong antenna as you know.
We have a CP6 owner in the club I'll ask him if he has had any problems or
knows of fixes.
Dave
UKMonitor
Looking at the design the main problem would seem to be the single
tuned radial for each band. Ideally to more effectively choke off
common mode currents on the coax feeder there should be at least a
pair mounted opposite each other for each band. You can visualise this
as being similar to the overhead radiation patterns of a an inverted L
and a T antenna.
Because of the common mode current flowing on the outer of the coax,
the feeder is acting as part of the antenna. Connecting additional
paths to earth at various points along the feeder will change the
common mode current distribuition and so modify the feed impedance.
This will change as you connect different equipment, patch cables and
provide different paths to earth. One turn of coax does not provide
enough choking impedance to make any difference.
The solution is to fit a good 1:1 ferrite balun (see this month's
Radcom for a design that is likey to work) at the feed point, and
possibly another on the antenna side of the coax where you have
provided your earth connection, ideally just before it entres your
property.
UKM
David
ATU there is a good chance the matching unit which sits just above the radials
could be burnt out.
Dave
Conor
Conor
> Looking at the design the main problem would seem to be the single
> tuned radial for each band. Ideally to more effectively choke off
> common mode currents on the coax feeder there should be at least a
> pair mounted opposite each other for each band. You can visualise this
> as being similar to the overhead radiation patterns of a an inverted L
> and a T antenna.
>
OK...
> Because of the common mode current flowing on the outer of the coax,
> the feeder is acting as part of the antenna. Connecting additional
> paths to earth at various points along the feeder will change the
> common mode current distribuition and so modify the feed impedance.
> This will change as you connect different equipment, patch cables and
> provide different paths to earth. One turn of coax does not provide
> enough choking impedance to make any difference.
>
Yeah, I looked at that and thought it was nigh on pointless but still
gave it a go to ensure I was installing it to their instructions.
Interesting that one transceiver was happy with it but another wasn't.
> The solution is to fit a good 1:1 ferrite balun (see this month's
> Radcom for a design that is likey to work) at the feed point, and
> possibly another on the antenna side of the coax where you have
> provided your earth connection, ideally just before it entres your
> property.
>
I've got a stack of ferrite rings so I'll have a bash at that. Why do I
get the feeling its like those short white plastic stubby things that
rely on using the feeder as part of the antenna in order to work?
Conor
hundred
kHz on 80m but it may be a possibility. Continuity is still OK to the
end of the vertical section and each radial though.
Jim.GM4DHJ/P...trailer trash located in South Ayrshire...
"Conor" <co...@gmx.co.uk> wrote in message
news:84icjj...@mid.individual.net...
> On 06/05/2010 17:25, Jim GM4DHJ in the Radio Shack ... wrote:
>>> Ultimately, it'll still be a crap antenna but at least it's given me
>>> something to fill the time for a couple of days.
>>>
>>
>> that's nice ...
>>
>>
> It is now its sunny :-)
>
Conor
Took it down today and decided to completely take it apart. When I took
apart the "DC Matching Section", there was another example of Diamonds
wonderful engineering. Basically there's a female to female SO239
connector in the base. Into the part that's inside the tube goes the PCB
which basically consists of two coils round a ferrite rod, an inductor
and three ceramic capacitors. It is completely uninsulated and it has
two solder pads which are so it can be soldered to the outer of the
female to female SO239 connector. Anyway, that solder had broken so it
was making an intermittent connection and therefore the braid of the
co-ax became a counterpoise when the connection was broken. In addition
to that, the uninsulated coils were able to come into contact with the
tube as the PCB was basically free floating at one end.
So I re-engineered the DC matching section. Wrapped the whole thing in
insulation tape to make sure none of the coils can touch the tube and
create a short. There is now a short stub of co-ax attached to the PCB
with the braid connected both to the PCB and the tube the section is
housed in. On the other end is a SO239 Chassis socket. This arrangement
allows for the minute flex there is in the bottom section when it's
windy and which was the cause of the whole problem.
With all the comments and posts there are on the interwibble about
people having to fix commercial antennas, one wonders if you're not far
better off just homebrewing everything.
Bob Martin
>
> With all the comments and posts there are on the interwibble about people
> having to fix commercial antennas, one wonders if you're not far better
> off just homebrewing everything.
In a word..yes!
Put up the longest doublet you can, it doesn't matter if the ends are dog
legged or droop down a bit. A 10m roach pole makes a good support.
Feed it with 300 or 450 ohm ribbon feeder or even make your own twin
feeder.All the way back to the shack and into one of the many cheap auto
ATUs via a balun, assuming that your rig doesn't have a built in ATU or its
range won't deal with SWR >3 (most infact). I find that the impedance
matching is usually ok on most bands except 40m where it's a bit sharp.
Don't listen to any of the folklore rubbish aboout twin feeder being
problematical, unless you are running it next to metal guttering or through
metal framed windows then its absolutely fine. Mine sits in a bundle with
several coax feeders and earth leads as it exits the the house through an
old tumble dryer vent hole and its fine, no RF feedback. If you can get
40m of wire up then you'll be fine on 80 thru 6 and most AATU's will bash it
down on 160 too.
For one of mine I run the 450ohm back to an SGC230 coupler with one wire
going to aerial and other to earth but at �200+ on ebay or �300 new the SGC
is hardly a budget choice, but they are flexible and v useful esp /P.
I also have a 10m wire running up a roach pole and tuned with another SGC
and that works great from 80 thru 10 and has given me loads of EU/US
contacts.
For 6m you are better off with a wire quarter wave GP for V/P and either a
dipole/HALO (sods to tune) or Hentenna for H/P. All can be home brewed out
of wire, bamboo, chewing gum and sealing wax for next to nothing and will
perform absolutely fine for most regular use.
Alternatively, get mithered with planning permission, blow �20K on a LUSO
and put up a MONSTIR. �30K worse off after all the bits and your
station's performance is unlikely to be �30K better IMHO but YMMV.
I'd spend money on one of the many VNAs out there (i use the miniVNA and
it's great) as that will save you loads of time trimming for resonance,
especially if the configuration is not a perfect straight horizontal run as
this can mess up the resonance point from that calculated, and its a boon
for setting up mobile whips
Enjoy and don't fall out of the tree like I did!!
Jim G7NKS
Gareth Evans G4SDW
news:o_OFn.1889$M17...@newsfe02.ams2...
> Put up the longest doublet you can
Doublet? Hose? Is that where the ladder comes from?
Conor
> snip
>>
>> With all the comments and posts there are on the interwibble about people
>> having to fix commercial antennas, one wonders if you're not far better
>> off just homebrewing everything.
>
> In a word..yes!
>
> Put up the longest doublet you can, it doesn't matter if the ends are dog
> legged or droop down a bit. A 10m roach pole makes a good support.
>
seems to be the best combination. Even Windoms require a tuner.
> Don't listen to any of the folklore rubbish aboout twin feeder being
> problematical, unless you are running it next to metal guttering or through
> metal framed windows then its absolutely fine.
Ah, I read a trick about doing that - basically to use two pieces of
co-ax spaced with the centers about the same as the ladder line.
> For one of mine I run the 450ohm back to an SGC230 coupler with one wire
> going to aerial and other to earth but at �200+ on ebay or �300 new the SGC
> is hardly a budget choice, but they are flexible and v useful esp /P.
>
> I also have a 10m wire running up a roach pole and tuned with another SGC
> and that works great from 80 thru 10 and has given me loads of EU/US
> contacts.
>
<snip>
What are you using for an earth, just a ground rod or a radial/mesh network?
> Enjoy and don't fall out of the tree like I did!!
>
I wish I had some here to fall out of, lol.
Bob Martin
> On 10/05/2010 08:56, Bob Martin wrote:
>> snip
>>>
>>> With all the comments and posts there are on the interwibble about
>>> people
>>> having to fix commercial antennas, one wonders if you're not far better
>>> off just homebrewing everything.
>>
>> In a word..yes!
>>
>> Put up the longest doublet you can, it doesn't matter if the ends are dog
>> legged or droop down a bit. A 10m roach pole makes a good support.
>>
> I've come to the conclusion that one of those with an automatic tuner
> seems to be the best combination. Even Windoms require a tuner.
>
>
With an auto ATU (I use LDG and SGC ones) most bits of wire over 20ft can be
tamed and made to work well. I also have a Palstar AT2K for QRO and that's
great too but manual of course.
>> Don't listen to any of the folklore rubbish aboout twin feeder being
>> problematical, unless you are running it next to metal guttering or
>> through
>> metal framed windows then its absolutely fine.
>
> Ah, I read a trick about doing that - basically to use two pieces of co-ax
> spaced with the centers about the same as the ladder line.
I just run some 450 ohm twin line feeder out through vent hole in brick wall
and then up and along garage wall, plastic guttering and wooden fence and
finally up a wooden mast to doublet centre. Twin feeder is virtually
lossless at HF up to around 100m or so and a damn sight cheaper than RG213
or Ecoflex/Westflex. Just watch the bend radii tho as it doesn't like
coming back on itself too sharpishly
>
>
>> For one of mine I run the 450ohm back to an SGC230 coupler with one wire
>> going to aerial and other to earth but at �200+ on ebay or �300 new the
>> SGC
>> is hardly a budget choice, but they are flexible and v useful esp /P.
>>
>
>> I also have a 10m wire running up a roach pole and tuned with another SGC
>> and that works great from 80 thru 10 and has given me loads of EU/US
>> contacts.
>>
> <snip>
>
> What are you using for an earth, just a ground rod or a radial/mesh
> network?
I have several ground rods/pipes all cross bonded and bonded to some mesh
that was laid down when we had drive/patio block paved, but if you can get a
few good bits of copper pipe banged into that soft wet northern irish soil
then you'll be fine. you might want to add some radials, the books say 16 @
0.l lambda of the lowest frequency used but just do as many as you can
afford time/money wise, cut them as long as you can make them and dont have
them too bent.
If you can get an old scrap copper water cylinder then dig a hole and bury
it, I kid you not, it does work well having seen it done at a friends. I'm
looking out for one but at current scrap prices they are not to be found
>
>> Enjoy and don't fall out of the tree like I did!!
>>
> I wish I had some here to fall out of, lol.
It's only the last inch that hurts!
10m roach poles @ �17 a throw are your friends and a couple of T/K brackets
on house apex/chimney with 1.5" x 5' swaged poles on. You can even mount a
dummy TV antenna on to disguise. For 20m and up the 10m pole gives you the
magical lambda/2 height and it still gives medium dx performance on 40m.
Height is good in theory but its not all its cracked up to be in "the real
world" and most wires at 5m+ will do well and certainly on �/dB basis knock
spots of commercial verticals and beams/towers
Yes I know that a 160m monobander on a 100ft lattice LUSO is a world spanner
but hey ho we don't all live at RAF Croughton and have ECB bail out funds
available to buy it, maybe if I win the lottery? I'll need to buy a ticket
first though.
Enjoy and keep us posted as to how you get on.
Conor
<snip>
> Enjoy and keep us posted as to how you get on.
Will do. A bit busy with things but I'm always messing with bits of wire.