Stainless steel is awful at conducting electricity - so it won't make a
very efficient antenna. But how much it really matters, I don't know.
You can coat it with silver or copper, only the outer few microns conduct HF
(skin-effect)

Wim

On Sun, 03 Aug 2003 22:51:50 -0700, Roy Lewallen
wrote:

The short answer is that stainless probably won't make a noticeable
difference in loss, and therefore won't make a significant difference in Q.


[thorough-sounding explanation snipped]

Thanks, Roy. Sounds like i should be okay with ss at 40Mhz for this
purpose, then. I've been up to see my supplier in N. London today and
returned with a good selection of various ss spring wire to try out.
I'm given to understand that the rx antenna length isn't that
important with this r/c stuff, so I guess 30-35 inches should be fine.
I'll mount it in a conical well with curved sides as someone else
suggested to minimise any stressing.
--

"I believe history will be kind to me, since I intend
to write it." - Winston Churchill

On Sun, 03 Aug 2003 22:51:50 -0700, Roy Lewallen
wrote:

The short answer is that stainless probably won't make a noticeable
difference in loss, and therefore won't make a significant difference in Q.


[thorough-sounding explanation snipped]

Thanks, Roy. Sounds like i should be okay with ss at 40Mhz for this
purpose, then. I've been up to see my supplier in N. London today and
returned with a good selection of various ss spring wire to try out.
I'm given to understand that the rx antenna length isn't that
important with this r/c stuff, so I guess 30-35 inches should be fine.
I'll mount it in a conical well with curved sides as someone else
suggested to minimise any stressing.
--

"I believe history will be kind to me, since I intend
to write it." - Winston Churchill

In article ,
Paul Burridge wrote:

Thanks, Roy. Sounds like i should be okay with ss at 40Mhz for
this purpose, then. I've been up to see my supplier in N. London
today and returned with a good selection of various ss spring
wire to try out. I'm given to understand that the rx antenna
length isn't that important with this r/c stuff, so I guess 30-35
inches should be fine. I'll mount it in a conical well with
curved sides as someone else suggested to minimise any stressing.

Paul, it sounds like you need to get yourself a CPC catalogue,
pdq. It is similar to RS/Farnell, but the product range is more
aligned to your specific needs.

eg, In the Aerial section there are standard flexible and
super-flexible whip aerials, for cars. Wideband AM-FM reception,
complete with adjustable mounting block and output cable+plug.
About 340mm long on avg. Prices range from £2:92, to a horrific
£4:86.

Note also that CPC does a range of build-it-yourself kits. eg,
Part number HK00224 is a wideband antenna amplifier kit. Metal
cased (24x36x86mm), with 22dB of gain over the range 10-150MHz.
Price is a bank-breaking £7:49.

See http://www.cpc.co.uk or 08701 202530 for a printed
catalogue or CDROM. Farnell own CPC, so if you have a
Farnell account you also automatically have a CPC account.

--
Tony Williams.

In article ,
Paul Burridge wrote:

Thanks, Roy. Sounds like i should be okay with ss at 40Mhz for
this purpose, then. I've been up to see my supplier in N. London
today and returned with a good selection of various ss spring
wire to try out. I'm given to understand that the rx antenna
length isn't that important with this r/c stuff, so I guess 30-35
inches should be fine. I'll mount it in a conical well with
curved sides as someone else suggested to minimise any stressing.

Paul, it sounds like you need to get yourself a CPC catalogue,
pdq. It is similar to RS/Farnell, but the product range is more
aligned to your specific needs.

eg, In the Aerial section there are standard flexible and
super-flexible whip aerials, for cars. Wideband AM-FM reception,
complete with adjustable mounting block and output cable+plug.
About 340mm long on avg. Prices range from £2:92, to a horrific
£4:86.

Note also that CPC does a range of build-it-yourself kits. eg,
Part number HK00224 is a wideband antenna amplifier kit. Metal
cased (24x36x86mm), with 22dB of gain over the range 10-150MHz.
Price is a bank-breaking £7:49.

See http://www.cpc.co.uk or 08701 202530 for a printed
catalogue or CDROM. Farnell own CPC, so if you have a
Farnell account you also automatically have a CPC account.

--
Tony Williams.

Paul Burridge wrote:
On Sat, 2 Aug 2003 18:24:44 -0500, "john graesser"
wrote:


Does it have to be a whip antenna? Why not try a horizontal circular loop?
Since you are working line of sight to the robot, the signal loss from going
from vertical to horizontal shouldn't matter much unless your transmitter is
extremely low power. A loop could be mounted inside a wooden or fiberglas
body and be pretty safe from attack.


If I believed this idea was workable I'd have implemented it by now.
You need to bear in mind that immediately beneath the polycarbonate
surface armor, there's a hulking great metal framework. Consequently,
sandwiching the antenna between the armour and the frame is going to
lead to unacceptable loss of radiated energy, I'd have thought. Unless
anyone knows differently..

Frequency limits prevent slot antennas in plate metal armor?

If so, loop antenna on top of the polycarb, with another
layer on top of that? You need a certain amount of standoff;
how much at your allowed frequencies? It'll amount to a box
or block of plastic stuck on the 'bot, but should be
relatively invulnerable.

Mark L. Fergerson

Paul Burridge wrote:
On Sat, 2 Aug 2003 18:24:44 -0500, "john graesser"
wrote:


Does it have to be a whip antenna? Why not try a horizontal circular loop?
Since you are working line of sight to the robot, the signal loss from going
from vertical to horizontal shouldn't matter much unless your transmitter is
extremely low power. A loop could be mounted inside a wooden or fiberglas
body and be pretty safe from attack.


If I believed this idea was workable I'd have implemented it by now.
You need to bear in mind that immediately beneath the polycarbonate
surface armor, there's a hulking great metal framework. Consequently,
sandwiching the antenna between the armour and the frame is going to
lead to unacceptable loss of radiated energy, I'd have thought. Unless
anyone knows differently..

Frequency limits prevent slot antennas in plate metal armor?

If so, loop antenna on top of the polycarb, with another
layer on top of that? You need a certain amount of standoff;
how much at your allowed frequencies? It'll amount to a box
or block of plastic stuck on the 'bot, but should be
relatively invulnerable.

Mark L. Fergerson

On Tue, 05 Aug 2003 08:03:45 +0100, Tony Williams
wrote:

Paul, it sounds like you need to get yourself a CPC catalogue,
pdq. It is similar to RS/Farnell, but the product range is more
aligned to your specific needs.

Curious. I've never heard of 'em!

eg, In the Aerial section there are standard flexible and
super-flexible whip aerials, for cars. Wideband AM-FM reception,
complete with adjustable mounting block and output cable+plug.
About 340mm long on avg. Prices range from £2:92, to a horrific
£4:86.

Note also that CPC does a range of build-it-yourself kits. eg,
Part number HK00224 is a wideband antenna amplifier kit. Metal
cased (24x36x86mm), with 22dB of gain over the range 10-150MHz.
Price is a bank-breaking £7:49.

See http://www.cpc.co.uk or 08701 202530 for a printed
catalogue or CDROM. Farnell own CPC, so if you have a
Farnell account you also automatically have a CPC account.

Well I do already have a Farnell a/c so I'll give em a try! Thanks for
the suggestion.

--

"I believe history will be kind to me, since I intend
to write it." - Winston Churchill

On Tue, 05 Aug 2003 08:03:45 +0100, Tony Williams
wrote:

Paul, it sounds like you need to get yourself a CPC catalogue,
pdq. It is similar to RS/Farnell, but the product range is more
aligned to your specific needs.

Curious. I've never heard of 'em!

eg, In the Aerial section there are standard flexible and
super-flexible whip aerials, for cars. Wideband AM-FM reception,
complete with adjustable mounting block and output cable+plug.
About 340mm long on avg. Prices range from £2:92, to a horrific
£4:86.

Note also that CPC does a range of build-it-yourself kits. eg,
Part number HK00224 is a wideband antenna amplifier kit. Metal
cased (24x36x86mm), with 22dB of gain over the range 10-150MHz.
Price is a bank-breaking £7:49.

See http://www.cpc.co.uk or 08701 202530 for a printed
catalogue or CDROM. Farnell own CPC, so if you have a
Farnell account you also automatically have a CPC account.

Well I do already have a Farnell a/c so I'll give em a try! Thanks for
the suggestion.

--

"I believe history will be kind to me, since I intend
to write it." - Winston Churchill

In article ,
Barry Lennox wrote:

I presume you are operating at 35 MHz or so? So your losses in a
30" whip are already rather high, especially into a typical RC Rx
front-end, so the material will not count for much either way.

In the CPC catalogue there is a loaded whip antenna (AR71694),
intended for mobile use, where the whip is made from what they
describe as 17/7ph milspec stainless steel. It comes complete
with all fittings, and cable with 50 ohm connectors both ends.
They give the following spec;

Bandwidth: 26-28MHz (which is the UK's CB band).
Antenna Type: 5/8 Wave.
Impedance: 50 ohm.
SWR: Less than 1:1.5.
Whip Length: 1.35m.

Is it practical to think of cutting the whip shorter for
operation at 40MHz, and (even better) is it possible to
predict exactly how much has to be cut off the whip?

--
Tony Williams.