Questions about a 2m J-pole
 

Hi,

I'm new to amateur radio, and am looking to build my first antenna for
the 2m band. I intend to build the one at http://www.qsl.net/iz7ath/web/02_bre...ole/jp_eng.htm.
As this is my first, I have a couple of questions about it's
construction:

1) Can I use copper tubing instead of aluminium?
2) Are the tube diameters crucial?
3) The instructions seem to imply that I can use the longer of the
tubes to mount the antenna. Does this need to be insulated?
4) I'll be using the 2m band, max power 10 Watts, and a cable run of
no more than 20 meters. What sort of cable would be best fro the
feeder? (Ideally one that can be purchased from Maplin:
http://www.maplin.co.uk/Search.aspx?...did=3&doy=18m9)

Thanks.

Questions about a 2m J-pole
 

Den Tue, 18 Sep 2007 09:00:16 -0700 skrev Tom Corker:


1) Can I use copper tubing instead of aluminium?
Yes 10 or 12mm o.d. plummers coppertubing and fittings makes a great j-
pole

http://www.n7qvc.com/amateur_radio/copper.html

This one works great


2) Are the tube diameters crucial?
No; but for all antennas wider material gives wider bandwith

3) The instructions seem to imply that I can use the longer of the tubes
to mount the antenna. Does this need to be insulated?

yes, mount it on a plastictube from the plummer

4) I'll be using
the 2m band, max power 10 Watts, and a cable run of no more than 20
meters. What sort of cable would be best fro the feeder? (Ideally one
that can be purchased from Maplin:
http://www.maplin.co.uk/Search.aspx?...6&MenuName=RF%
20Cable&FromMenu=y&worldid=3&doy=18m9)


RG213 will do, RG58 are too lossy on vhf.
Thanks.





--
Vy73 de OZ1GNN

Christian Treldal

Questions about a 2m J-pole
 

On 18 Sep, 17:52, Christian Treldal wrote:
Den Tue, 18 Sep 2007 09:00:16 -0700 skrev Tom Corker:



1) Can I use copper tubing instead of aluminium?

Yes 10 or 12mm o.d. plummers coppertubing and fittings makes a great j-
pole

http://www.n7qvc.com/amateur_radio/copper.html

This one works great

2) Are the tube diameters crucial?

No; but for all antennas wider material gives wider bandwith

3) The instructions seem to imply that I can use the longer of the tubes
to mount the antenna. Does this need to be insulated?

yes, mount it on a plastictube from the plummer

4) I'll be using
the 2m band, max power 10 Watts, and a cable run of no more than 20
meters. What sort of cable would be best fro the feeder? (Ideally one
that can be purchased from Maplin:
http://www.maplin.co.uk/Search.aspx?...6&MenuName=RF%

20Cable&FromMenu=y&worldid=3&doy=18m9)

RG213 will do, RG58 are too lossy on vhf.

Thanks.

--
Vy73 de OZ1GNN

Christian Treldal

Thanks for that. I'm thinking about going with the design you gave.
I'm also guessing I'll need to tune the antenna using an SWR meter. A
lot of the ones on ebay (UK) are listed as CB SWR meters. Will these
be OK for the 2m band?

Questions about a 2m J-pole
 

Thanks for that. I'm thinking about going with the design you gave.
I'm also guessing I'll need to tune the antenna using an SWR meter. A
lot of the ones on ebay (UK) are listed as CB SWR meters. Will these
be OK for the 2m band?
==========================
Not really , go for a proper SWR meter suitable for freqs up to 150 MHz
Even better ,buy or borrow an antenna analyser . The MFJ259 is rather
popular ,but there are others as well.


Frank GM0CSZ / KN6WH

Questions about a 2m J-pole
 

Tom,

Most of those CB SWR meters are good for HF and probably 6 meters or
so. My experience is that they are highly inaccurate at best, and
often completely unusable on 2 meters. I lend my Bird wattmeter out
frequently for people doing installations because of this.

Of course, there are so many units out there it is impossible to say
with certainty that they won't work, but that's what to expect. You
don't what an additional unknown in building up a new antenna.


--
Alan
WA4SCA

Questions about a 2m J-pole
 

Hi Tom

If you really feel like not spending money on a SWR meter you might like
to try the horrible but simple approach of making one out of a piece of
RG213 with the PVC stripped off, and thin teflon wire pushed under the
shield in the same mechanical arrangement of a SWR meter. A couple of
shottkeys, capacitors and resistors and you can read VSWR on a multimeter!

I'd even venture to suggest that replacing the line section in a CB
meter with this arrangement would yield a much more useful higher
frequency device. (And use BNC's or N sockets...)

I can see you all cringing!

Cheers Bob W5/VK2YQA

Tom Corker wrote:

Christian Treldal

Thanks for that. I'm thinking about going with the design you gave.
I'm also guessing I'll need to tune the antenna using an SWR meter. A
lot of the ones on ebay (UK) are listed as CB SWR meters. Will these
be OK for the 2m band?

Questions about a 2m J-pole
 

"Tom Corker" wrote in message
ups.com...

snip

Thanks for that. I'm thinking about going with the design you gave.
I'm also guessing I'll need to tune the antenna using an SWR meter. A
lot of the ones on ebay (UK) are listed as CB SWR meters. Will these
be OK for the 2m band?


Sometimes. It depends on the design. I have really fooled myself into
thinking I had done something wrong with the antenna, when the antenna was
fine but the meter was erroneously reporting high VSWR.

The only sure test, in my opinion, is to try the SWR meter into a known good
load, then (briefly) into a short and then into an open. The known good
load should, of course give you very low SWR, while the short and open
should give you very high VSWR.

I have one meter rated for HF which works not only on 2m, but also on 70 cm.

I've built about two dozen j-poles, most of them copper pipe . I love their
simplicity and ruggedness. One tip, if I may: If you can tune the antenna
for a low-VSWR point that falls inband, but it's not 1:1 no matter what, try
inserting a 100 pF capacitor at the feed point.

In the US, copper water pipe comes in three grades, K, L and M, in
increasing order of quality/cost. We also have "DWV" copper pipe for drains
and vents (non-pressure applications, I guess). Same over there?

73,
"Sal"
(KD6VKW)

Questions about a 2m J-pole
 

Must say that I second this, as the "sampleing" in MANY swr meters not
only DON'T read accurately, at VHF, but actually induce a "Impedence
Mis-Match" (and gives you a FALSE reading , at VHF) ! In fact, have
seen "Flat antennas, show some hideous SWR's " ! And, tho length is
of the antenna element is
the determining factor, you need a good meter if you want to minimize
the swr. As to insulating the J-Pole, BELOW the 2 vertical elements,
this shouldn't be necessary- and - keep in mind that this antenna wants
a Balanced feedline-, so, that your coax WON'T radiate! BUT- as you
probably will use (unbalanced) coax (No BALUN) that your coax becomes
PART of the antenna system ! But this should not present itself
as much of a problem, unless it lets RF into the RIG/Power Supply in
a quantity to cause problems in those devices! As to coax, use the
lowest loss you can afford, tho, again, in this instance, will mean
LITTLE! At 20 foot length, RG 58 should work fine! Just build it, get a
fairly good match to keep the rig happy, and enjoy! Jim NN7K


Alan WA4SCA wrote:
Tom,

Most of those CB SWR meters are good for HF and probably 6 meters or
so. My experience is that they are highly inaccurate at best, and
often completely unusable on 2 meters. I lend my Bird wattmeter out
frequently for people doing installations because of this.

Of course, there are so many units out there it is impossible to say
with certainty that they won't work, but that's what to expect. You
don't what an additional unknown in building up a new antenna.


--
Alan
WA4SCA

Questions about a 2m J-pole
 

In the US, copper water pipe comes in three grades, K, L and M, in
increasing order of quality/cost. We also have "DWV" copper pipe for drains
and vents (non-pressure applications, I guess). Same over there?
================
Question : Would any of the above grades of copper pipe affect the RF
radiation characteristics of the antenna ?

Frank GM0CSZ / KN6WH

Questions about a 2m J-pole
 

Bob Bob wrote:
Hi Tom

If you really feel like not spending money on a SWR meter you might like
to try the horrible but simple approach of making one out of a piece of
RG213 with the PVC stripped off, and thin teflon wire pushed under the
shield in the same mechanical arrangement of a SWR meter. A couple of
shottkeys, capacitors and resistors and you can read VSWR on a multimeter!

I'd even venture to suggest that replacing the line section in a CB
meter with this arrangement would yield a much more useful higher
frequency device. (And use BNC's or N sockets...)
==================================
Instead of using RG213 coax I would use a short piece of 75 Ohms coax
(here in the UK used for sat dish feeder) with air gap dielectric .
The 10 mm (3/8 inch) OD variety is particularly suitable .
Without removing the outer sheathing a bare or teflon insulated wire can
be readily pushed through.


Frank GM0CSZ / KN6WH

Questions about a 2m J-pole
 

Frank

Wouldn't you be concerned over presenting a slight Z bump of a 75 ohm
piece of material? I'll admit I cant see it making a huge difference,
but as one is building test gear it might pay to be pedantic.

I'd also be concerned that pushing wire into the air gap would lower the
Z in an unpredictable way. Pushing it just under the shield keeps it at
a reasonably fixed dielectric spacing from the inner conductor.

If it works however, then I won't argue!

Bob VK2YQA


Highland Ham wrote:
Instead of using RG213 coax I would use a short piece of 75 Ohms coax
(here in the UK used for sat dish feeder) with air gap dielectric .
The 10 mm (3/8 inch) OD variety is particularly suitable .
Without removing the outer sheathing a bare or teflon insulated wire can
be readily pushed through.

Questions about a 2m J-pole
 

Bob Bob wrote:
Frank

Wouldn't you be concerned over presenting a slight Z bump of a 75 ohm
piece of material? I'll admit I cant see it making a huge difference,
but as one is building test gear it might pay to be pedantic.

I'd also be concerned that pushing wire into the air gap would lower the
Z in an unpredictable way. Pushing it just under the shield keeps it at
a reasonably fixed dielectric spacing from the inner conductor.

If it works however, then I won't argue!
==========================
I'll check the anticipated 'bump' with the MFJ259B analyser.
First connected to a high quality professional dummy load good for freqs
to 2 GHz (ex cellnet industry),thereafter with the homebrew SWR sensor
inserted,testing in 2 stages : First with just the short piece of 75
ohms coax (obviously having the braid connected to chassis at one end
only) ;Secondly with the wire pushed into the air gap.

This is a useful and interesting NG thread.

Frank GM0CSZ / KN6WH

Questions about a 2m J-pole
 

Highland Ham wrote:
In the US, copper water pipe comes in three grades, K, L and M, in
increasing order of quality/cost. We also have "DWV" copper pipe for
drains
and vents (non-pressure applications, I guess). Same over there?
================
Question : Would any of the above grades of copper pipe affect the RF
radiation characteristics of the antenna ?


The answer depends upon whether you mean an effect that is noticible or
not. ;^)

73 de Mike KB3EIA -

Questions about a 2m J-pole
 

Michael Coslo wrote:
Highland Ham wrote:
In the US, copper water pipe comes in three grades, K, L and M, in
increasing order of quality/cost. We also have "DWV" copper pipe for
drains
and vents (non-pressure applications, I guess). Same over there?
================
Question : Would any of the above grades of copper pipe affect the RF
radiation characteristics of the antenna ?


The answer depends upon whether you mean an effect that is noticible
or not. ;^)
============================================
My question is directed to the different grades K,L and M ,whether any
particular grade would give better RF radiation performance .
It could be that the grade with the highest copper content gives the
best performance ,although I doubt that it will be measurable.
J-pole antennas I am familiar with are all made of aluminium,but copper
is of course better long term in an outdoor environment and electrical
contacts are reliable following soldering.

Frank GM0CSZ / KN6WH

Questions about a 2m J-pole
 

"Highland Ham" wrote in message
...
Michael Coslo wrote:
Highland Ham wrote:
In the US, copper water pipe comes in three grades, K, L and M, in
increasing order of quality/cost. We also have "DWV" copper pipe for
drains
and vents (non-pressure applications, I guess). Same over there?
================
Question : Would any of the above grades of copper pipe affect the RF
radiation characteristics of the antenna ?


The answer depends upon whether you mean an effect that is noticible
or not. ;^)
============================================
My question is directed to the different grades K,L and M ,whether any
particular grade would give better RF radiation performance .
It could be that the grade with the highest copper content gives the best
performance ,although I doubt that it will be measurable.
J-pole antennas I am familiar with are all made of aluminium,but copper is
of course better long term in an outdoor environment and electrical
contacts are reliable following soldering.

Frank GM0CSZ / KN6WH


-------------


I have made emergency VHF antennas from a hunk of 2x4 and two pieces of 3/8"
aluminum grounding wire. Then I get a piece of mini8x (any 50 ohm coax will
do), skin back the insulation until I have enough material to solder an
alligator clip onto the center lead and one onto the equi-distant piece of
shielding. I then drill two 3/8's diameter holes approximately 4" apart in
the hunk of 2x4. Calculate the 1/2 wavelenth of the band you wish to operate
on. Cut a hunk of 3/8" grounding wire to that length, straighten and then
insert it into one of the previously drilled 3/8" holes in the hunk of 2x4.
Cut another hunk of 3/8" aluminum grounding wire to exactly one half the
length of the first piece and then insert it into the remaining hole in the
2x4.

Connect the coax to your VHF rig via the PL-259 that you soldered onto the
end opposite the end with the alligator clips and plug it into your rig.
Clip the alligator clip fastened to the center coax conductor to the longest
piece of 3/8" wire (half wavelength) and the shield connected alligator clip
to the shorter wire protruding from the 2x4. Adjust the height of the two
clips (should be even with one another) for the lowest SWR. Voila! You're on
the air with an instant J-Pole antenna.

All of this can be enclosed in PVC plastic piping for use outdoors.


Ed, NM2K

Questions about a 2m J-pole
 

In article ,
Highland Ham wrote:

My question is directed to the different grades K,L and M ,whether any
particular grade would give better RF radiation performance .
It could be that the grade with the highest copper content gives the
best performance ,although I doubt that it will be measurable.

My recollection is that the basic difference between the various
grades is the thickness of the copper walls. The thicker-walled pipe
is what's preferred for outdoor/buried use and/or higher pressures
(e.g. use on the supply side of a house's water-pressure regulator).

RF current flows only through the skin of a conductor... it doesn't
penetrate very far into the body. One web calculator I found says
that the skin depth of a 144 MHz signal in copper is around 200
micro-inches, or 1/5000 of an inch. If the tubing wall is
much thicker than this, the additional thickness will have no
significant benefit in reducing resistive losses.

Since even the thinnest-walled (Schedule M) copper pipe has a wall
thickness which is about a hundred times more than the skin depth,
there's no electrical benefit to using thicker-walled tubing (Schedule
K or L).

Unless there's some mechanical reason to want to use the heavier-
schedule tubing, I'd just stick with Schedule M - it's lighter, less
expensive, and should be plenty stiff and strong for most
applications.

--
Dave Platt AE6EO
Friends of Jade Warrior home page: http://www.radagast.org/jade-warrior
I do _not_ wish to receive unsolicited commercial email, and I will
boycott any company which has the gall to send me such ads!

Questions about a 2m J-pole
 

Highland Ham wrote:
Question : Would any of the above grades of copper pipe affect the RF
radiation characteristics of the antenna ?

No.

Roy Lewallen, W7EL

Questions about a 2m J-pole
 

On Sep 19, 9:29 am, "Ed Cregger" wrote:
"Highland Ham" wrote in message

...



Michael Coslo wrote:
Highland Ham wrote:
In the US, copper water pipe comes in three grades, K, L and M, in
increasing order of quality/cost. We also have "DWV" copper pipe for
drains
and vents (non-pressure applications, I guess). Same over there?
================
Question : Would any of the above grades of copper pipe affect the RF
radiation characteristics of the antenna ?

The answer depends upon whether you mean an effect that is noticible
or not. ;^)
============================================
My question is directed to the different grades K,L and M ,whether any
particular grade would give better RF radiation performance .
It could be that the grade with the highest copper content gives the best
performance ,although I doubt that it will be measurable.
J-pole antennas I am familiar with are all made of aluminium,but copper is
of course better long term in an outdoor environment and electrical
contacts are reliable following soldering.

Frank GM0CSZ / KN6WH

-------------

I have made emergency VHF antennas from a hunk of 2x4 and two pieces of 3/8"
aluminum grounding wire. Then I get a piece of mini8x (any 50 ohm coax will
do), skin back the insulation until I have enough material to solder an
alligator clip onto the center lead and one onto the equi-distant piece of
shielding. I then drill two 3/8's diameter holes approximately 4" apart in
the hunk of 2x4. Calculate the 1/2 wavelenth of the band you wish to operate
on. Cut a hunk of 3/8" grounding wire to that length, straighten and then
insert it into one of the previously drilled 3/8" holes in the hunk of 2x4.
Cut another hunk of 3/8" aluminum grounding wire to exactly one half the
length of the first piece and then insert it into the remaining hole in the
2x4.

Connect the coax to your VHF rig via the PL-259 that you soldered onto the
end opposite the end with the alligator clips and plug it into your rig.
Clip the alligator clip fastened to the center coax conductor to the longest
piece of 3/8" wire (half wavelength) and the shield connected alligator clip
to the shorter wire protruding from the 2x4. Adjust the height of the two
clips (should be even with one another) for the lowest SWR. Voila! You're on
the air with an instant J-Pole antenna.

All of this can be enclosed in PVC plastic piping for use outdoors.

Ed, NM2K

Normally, a J-pole has parallel conductors at the bottom 1/4
wavelength, with one of the conductors extending above that 1/4 wave
section for an additional 1/2 wavelength above that. That would be a
3/4 wave piece of wire and a 1/4 wave piece of wire. If I'm reading
your description correctly, you're describing an antenna in which
there's the 1/4 wave of parallel conductors, but then only 1/4 wave
above that of the "unaccompanied" part of the half-wave piece. Also,
do you not connect the two pieces of wire together at the end?

I've seen J-pole designs fed at the bottom end, and I've seen them
with the bottom end shorted and the feed line tapped up on the
parallel section, but haven't heard of one fed tapped up on the
parallel section without the bottom shorted.

Cheers,
Tom

Questions about a 2m J-pole
 

"K7ITM" wrote in message
ups.com...
On Sep 19, 9:29 am, "Ed Cregger" wrote:
"Highland Ham" wrote in message

...



Michael Coslo wrote:
Highland Ham wrote:
In the US, copper water pipe comes in three grades, K, L and M, in
increasing order of quality/cost. We also have "DWV" copper pipe
for
drains
and vents (non-pressure applications, I guess). Same over there?
================
Question : Would any of the above grades of copper pipe affect the RF
radiation characteristics of the antenna ?

The answer depends upon whether you mean an effect that is
noticible
or not. ;^)
============================================
My question is directed to the different grades K,L and M ,whether any
particular grade would give better RF radiation performance .
It could be that the grade with the highest copper content gives the
best
performance ,although I doubt that it will be measurable.
J-pole antennas I am familiar with are all made of aluminium,but copper
is
of course better long term in an outdoor environment and electrical
contacts are reliable following soldering.

Frank GM0CSZ / KN6WH

-------------

I have made emergency VHF antennas from a hunk of 2x4 and two pieces of
3/8"
aluminum grounding wire. Then I get a piece of mini8x (any 50 ohm coax
will
do), skin back the insulation until I have enough material to solder an
alligator clip onto the center lead and one onto the equi-distant piece
of
shielding. I then drill two 3/8's diameter holes approximately 4" apart
in
the hunk of 2x4. Calculate the 1/2 wavelenth of the band you wish to
operate
on. Cut a hunk of 3/8" grounding wire to that length, straighten and then
insert it into one of the previously drilled 3/8" holes in the hunk of
2x4.
Cut another hunk of 3/8" aluminum grounding wire to exactly one half the
length of the first piece and then insert it into the remaining hole in
the
2x4.

Connect the coax to your VHF rig via the PL-259 that you soldered onto
the
end opposite the end with the alligator clips and plug it into your rig.
Clip the alligator clip fastened to the center coax conductor to the
longest
piece of 3/8" wire (half wavelength) and the shield connected alligator
clip
to the shorter wire protruding from the 2x4. Adjust the height of the two
clips (should be even with one another) for the lowest SWR. Voila! You're
on
the air with an instant J-Pole antenna.

All of this can be enclosed in PVC plastic piping for use outdoors.

Ed, NM2K

Normally, a J-pole has parallel conductors at the bottom 1/4
wavelength, with one of the conductors extending above that 1/4 wave
section for an additional 1/2 wavelength above that. That would be a
3/4 wave piece of wire and a 1/4 wave piece of wire. If I'm reading
your description correctly, you're describing an antenna in which
there's the 1/4 wave of parallel conductors, but then only 1/4 wave
above that of the "unaccompanied" part of the half-wave piece. Also,
do you not connect the two pieces of wire together at the end?

I've seen J-pole designs fed at the bottom end, and I've seen them
with the bottom end shorted and the feed line tapped up on the
parallel section, but haven't heard of one fed tapped up on the
parallel section without the bottom shorted.

Cheers,
Tom


--------------


Try it, just as I described it. It works and works well.

No, the bottoms are not connected, but there is a version that works with
that connection.


Ed Cregger, NM2K

Questions about a 2m J-pole
 

"Highland Ham" wrote in message
...
In the US, copper water pipe comes in three grades, K, L and M, in
increasing order of quality/cost. We also have "DWV" copper pipe for
drains
and vents (non-pressure applications, I guess). Same over there?
================
Question : Would any of the above grades of copper pipe affect the RF
radiation characteristics of the antenna ?



I don't think so -- just the cost. Aluminum, which is less conductive than
any common copper alloy, makes fine antennas.

By the way, please refer to the copper pipe section at
http://www.homedepot.com/webapp/wcs/...?pn=Pipes&lang
Id=-1&storeId=10051&catalogId=10053 (I think I had the price/quality
expressed backwards in my original post.)

"Sal"

Questions about a 2m J-pole
 

Dave Platt wrote:
In article ,
Highland Ham wrote:

My question is directed to the different grades K,L and M ,whether any
particular grade would give better RF radiation performance .
It could be that the grade with the highest copper content gives the
best performance ,although I doubt that it will be measurable.

My recollection is that the basic difference between the various
grades is the thickness of the copper walls. The thicker-walled pipe
is what's preferred for outdoor/buried use and/or higher pressures
(e.g. use on the supply side of a house's water-pressure regulator).

RF current flows only through the skin of a conductor... it doesn't
penetrate very far into the body. One web calculator I found says
that the skin depth of a 144 MHz signal in copper is around 200
micro-inches, or 1/5000 of an inch. If the tubing wall is
much thicker than this, the additional thickness will have no
significant benefit in reducing resistive losses.

Since even the thinnest-walled (Schedule M) copper pipe has a wall
thickness which is about a hundred times more than the skin depth,
there's no electrical benefit to using thicker-walled tubing (Schedule
K or L).

Unless there's some mechanical reason to want to use the heavier-
schedule tubing, I'd just stick with Schedule M - it's lighter, less
expensive, and should be plenty stiff and strong for most
applications.


----------------

Go the cheapest way, as recommended above. You can't tell the difference
between the various grades without laboratory grade measuring equipment.
Surely no one receiving your signal could ever tell the difference.

Ed, NM2K

Questions about a 2m J-pole
 

OK, I've built my J-pole and it's looking quite good. In the end, I
went for 22mm copper tubing as I had some spare. I've still not
decided on the coax though. I've measured the run, and I'll be needing
12 meters (39 feet). In addition to the RG213, I've managed to find a
source of 'low-loss mini 8' (RG-8X). The RG213 is £1.40 per meter, and
the RG-8x is £0.65
per meter. Is the RG213 worth the difference on VHF?

Thanks for all your advice and help.

Questions about a 2m J-pole
 

Tom Corker wrote:
OK, I've built my J-pole and it's looking quite good. In the end, I
went for 22mm copper tubing as I had some spare. I've still not
decided on the coax though. I've measured the run, and I'll be needing
12 meters (39 feet). In addition to the RG213, I've managed to find a
source of 'low-loss mini 8' (RG-8X). The RG213 is £1.40 per meter, and
the RG-8x is £0.65
per meter. Is the RG213 worth the difference on VHF?

Thanks for all your advice and help.



-------------


To me, no, it isn't worth the difference in price, nor the hassle in
handling the thicker coax. Were I working weak signal modes, it might be
a different matter, but then I would use hardline or 9913 at the minimum.

Ed, NM2K

Questions about a 2m J-pole
 

Tom Corker wrote:
Is the RG213 worth the difference on VHF?

Only you can answer that question. For 12 meters on a
flat line on 2m, RG213 has ~1dB loss and RG8x has
~1.5dB of loss. (LMR400 has ~0.6dB of loss.) Is
double the price worth 0.5dB to you?

http://www.vk1od.net/tl/tllc.php
--
73, Cecil http://www.w5dxp.com

Questions about a 2m J-pole
 

"Tom Corker" wrote in message
oups.com...
OK, I've built my J-pole and it's looking quite good. In the end, I
went for 22mm copper tubing as I had some spare. I've still not
decided on the coax though. I've measured the run, and I'll be needing
12 meters (39 feet). In addition to the RG213, I've managed to find a
source of 'low-loss mini 8' (RG-8X). The RG213 is £1.40 per meter, and
the RG-8x is £0.65
per meter. Is the RG213 worth the difference on VHF?


Tom,

On VHF FM, a dB or two of signal will affect a marginal contact. In your
situation, however, the better cable provides only slightly more than half a
dB of signal, hardly worth the extra expense.

I used http://www.ocarc.ca/coax.htm for that comparison.

Other comparison tables and charts are widely available on the Internet with
a search for "Coaxial Cable" Loss. The sample table below will line up
nicely in a monospace font, like Courier.

Coax Cable Type Signal Loss per 100 ft
Loss* RG-174 RG-58 RG-8X RG-213 RG-6 RG-11 RF-9914 RF-9913
1MHz 1.9dB 0.4dB 0.5dB 0.2dB 0.2dB 0.2dB 0.3dB 0.2dB
10MHz 3.3dB 1.4dB 1.0dB 0.6dB 0.6dB 0.4dB 0.5dB 0.4dB
50MHz 6.6dB 3.3dB 2.5dB 1.6dB 1.4dB 1.0dB 1.1dB 0.9dB
100MHz 8.9dB 4.9dB 3.6dB 2.2dB 2.0dB 1.6dB 1.5dB 1.4dB
200MHz 11.9dB 7.3dB 5.4dB 3.3dB 2.8dB 2.3dB 2.0dB 1.8dB
400MHz 17.3dB 11.2dB 7.9dB 4.8dB 4.3dB 3.5dB 2.9dB 2.6dB
700MHz 26.0dB 16.9dB 11.0dB 6.6dB 5.6dB 4.7dB 3.8dB 3.6dB
900MHz 27.9dB 20.1dB 12.6dB 7.7dB 6.0dB 5.4dB 4.9dB 4.2dB
1GHz 32.0dB 21.5dB 13.5dB 8.3dB 6.1dB 5.6dB 5.3dB 4.5dB
Imped 50ohm 50ohm 50ohm 50ohm 75ohm 75ohm 50ohm 50ohm