(scooterspal) wrote in
:

Hello and thanks for ahy help you can provide.

I have a small assisted hearing type transmitter that normally uses
the shield of the mic cable for the antenna. I need to change to a
fixed antenna for a particular application where there is no mic
cable to extend out.

The manufacturer says the antenna wire for this 651.85Mhz unit
should be 48" long.

Can anyone tell me what that would equal in a rubber ducky antenna?

You appear to be posting from the US, so I thought I'd mention that if
this transmitter is an unlicensed "Part 15 Intentional Radiator" (I
don't know what an "assisted hearing" transmitter is, so I might be
wildly off base), you'll be running afoul of 47CFR15.204(c) if you use
any antenna other than the one supplied with it.

Just trying to help :-)

--
Bert Hyman | St. Paul, MN |

Bert Hyman wrote:

You appear to be posting from the US, so I thought I'd mention that if
this transmitter is an unlicensed "Part 15 Intentional Radiator"

This is a legal device. You can find them at Comtek (www.comtek.com).

I'm just trying to replace the antenna system they are using, which is
a lapel mic with about 48" of shielded cable between the 1/2" connector
and the mic head, with a fixed, shorter high-gain (rubber ducky type)
antenna.

Can anyone help me to accomplish this? What do I need in terms of
the antenna... the exact type?

Thanks.

"scooterspal" wrote in message
...
Bert Hyman wrote:

You appear to be posting from the US, so I thought I'd mention that if
this transmitter is an unlicensed "Part 15 Intentional Radiator"

This is a legal device. You can find them at Comtek (www.comtek.com).

I'm just trying to replace the antenna system they are using, which is
a lapel mic with about 48" of shielded cable between the 1/2" connector
and the mic head, with a fixed, shorter high-gain (rubber ducky type)
antenna.

Can anyone help me to accomplish this? What do I need in terms of
the antenna... the exact type?

Thanks.

'high-gain rubber ducky' isn't that an oxymoron?? rubber ducks are usually
much lossier than full size antennas.

scooterspal wrote:

Bert Hyman wrote:

You appear to be posting from the US, so I thought I'd mention that if
this transmitter is an unlicensed "Part 15 Intentional Radiator"

I'm confused, now.

Their web site (www.comtek.com) shows the newer models operate in the
216-217Mhz band. I have a frequency counter. Is there a way I can make a
wire loop and set the trasmitter near it to pick off the operating
frequency?

Thanks.

"scooterspal" wrote in message
...
scooterspal wrote:

Bert Hyman wrote:

You appear to be posting from the US, so I thought I'd mention that if
this transmitter is an unlicensed "Part 15 Intentional Radiator"

I'm confused, now.

Their web site (www.comtek.com) shows the newer models operate in the
216-217Mhz band. I have a frequency counter. Is there a way I can make a
wire loop and set the trasmitter near it to pick off the operating
frequency?

Thanks.

yes, make a wire loop, put the transmitter near it and read the frequency...
just like you said.

(scooterspal) wrote in
:

Bert Hyman wrote:

You appear to be posting from the US, so I thought I'd mention that
if this transmitter is an unlicensed "Part 15 Intentional Radiator"

This is a legal device. You can find them at Comtek
(www.comtek.com).

I didn't say illegal, I said unlicensed.

--
Bert Hyman | St. Paul, MN |

OK. I have tested the frequency and found it to be 75.489Mhz. Should
have done this first, sorry for the confusion. Comtek did make systems
that operated betweeh 72 and 76Mhz. This is one of those.

That said, where do I stand antenna wise?

Thanks!

On May 30, 12:50 pm, scooterspal wrote:
OK. I have tested the frequency and found it to be 75.489Mhz. Should
have done this first, sorry for the confusion. Comtek did make systems
that operated betweeh 72 and 76Mhz. This is one of those.

That said, where do I stand antenna wise?

Thanks!

Depending on how large a distance you want it to cover, you may get by
with a considerably shorter antenna than the 48 inch recommended
size. But you also didn't say, that I could see, that there was a
problem using a 48" piece of wire. Obviously it's not too critical
since in use the mic cable can be bent in all sorts of different
shapes and it still operates. In other words, try to not make this
more difficult than it needs to be. If you need the mechanical
antenna to be shorter than 48 inches, just wind that length of wire in
a spiral, spaced out as much as you can accommodate. Try that and see
how it works. Easy enough? If you need higher performance, that's
possible, but in general very short antennas won't be as efficient as
straight antennas long enough to be self-resonant at the operating
frequency. If you need good performance from a short antenna, get a
system that operates at a higher frequency.

Cheers,
Tom

K7ITM wrote:

If you need the mechanical
antenna to be shorter than 48 inches, just wind that length of wire in
a spiral, spaced out as much as you can accommodate. Try that and see
how it works. Easy enough? If you need higher performance, that's
possible, but in general very short antennas won't be as efficient as
straight antennas long enough to be self-resonant at the operating
frequency...

Is that all a rubber ducky antenna is? 48" of wire wound around a
flexible core of some type?

If so, what do I look for (type, model, etc.) if I want to purchase
one to try out?

Is that all a rubber ducky antenna is? 48" of wire wound around a
flexible core of some type?

No, that isn't all that a 'rubber duck' antenna is, wish it were
that simple. Since the question was asked, I have to assume that you
aren't exactly familiar with what a transmitter 'looks' for in an
antenna, or how that 'looked for' thing is arrived at. (And if you
aren't sort of 'involved' in radio stuff, why should you be?) Once
you learn about all that stuff it really isn't all that hard to
figure. But that 'learning' can certainly be a real chore!
- 'Doc