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.

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

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?

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

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

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?

"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)

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

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

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