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.

On Sat, 02 Aug 2003 21:55:22 +0100, Paul Burridge
wrote:

On Sat, 2 Aug 2003 16:40:43 +0100, "cpemma"
wrote:

The alloy is Type 301 (17% chromium, 7% nickel stainless steel) hard drawn
wire, or even better is a 17/7PH (precipitation hardening) grade that our
firm once produced for tank aerials, that also may take a few knocks.

Both (especially the PH grade) need a final heat-treatment (420C for a few
minutes IIRC) for ultimate spring properties, but to get such a tight bend
you'd need quite a thin wire. It's a matter of the proof strain or limit of
proportionality, how much the outer skin can stretch without taking a
permanent set, compared to the neutral central axis, on the bend.

There speaks a man who obviously knows what he's talking about. Yes, I
believe we can order 301 from our guy in N. London who's very
accommodating on such matters. Thanks for a valuable steer!
Just one point, though: is stainless steel a reasonable radiator of RF
energy?

Unless your tx is in the kW range the slightly higher resistivity is
unlikely to make a difference.

- YD.

On Sat, 02 Aug 2003 21:55:22 +0100, Paul Burridge
wrote:

On Sat, 2 Aug 2003 16:40:43 +0100, "cpemma"
wrote:

The alloy is Type 301 (17% chromium, 7% nickel stainless steel) hard drawn
wire, or even better is a 17/7PH (precipitation hardening) grade that our
firm once produced for tank aerials, that also may take a few knocks.

Both (especially the PH grade) need a final heat-treatment (420C for a few
minutes IIRC) for ultimate spring properties, but to get such a tight bend
you'd need quite a thin wire. It's a matter of the proof strain or limit of
proportionality, how much the outer skin can stretch without taking a
permanent set, compared to the neutral central axis, on the bend.

There speaks a man who obviously knows what he's talking about. Yes, I
believe we can order 301 from our guy in N. London who's very
accommodating on such matters. Thanks for a valuable steer!
Just one point, though: is stainless steel a reasonable radiator of RF
energy?

Unless your tx is in the kW range the slightly higher resistivity is
unlikely to make a difference.

- YD.