I´ve been given an old long range cordless telephone. The base station
takes two antennas (transmit and receive) but only came with the RX
antenna. I can make a homebrew TX antenna but need to know the
transmission frequency in order to do so.

Naturally the unit came with no manual, no specs, and no schematic. No
manufacturer´s name appears outside or inside the equipment, not even on
the PCBs. There are no FCC or UL numbers to look up. I do have a clue,
however: The base unit´s reception antenna is clearly labled ¨RX: 70
MHz¨. And inside the handheld unit there is a component stamped ¨70.365
H.ELE. CH23 1J¨. So 70.365 MHz seems to be the base unit´s RX frequency.
Also inside the handheld are two apparently identical commponents stamped
39.040 and 10.245 respectively. So perhaps one of these is the base
unit´s TX frequency in MHz?

To test my idea I looked inside the base unit. There are four apparently
identical components, stamped 59.665, 10.245, 49.740, and ¨10M 15A¨,
respectively. So is it safe to conclude that 10.245 MHz is the base
unit´s TX frequency and that I should make the antenna for that frequency?

--
Warren Post
Santa Rosa de Copán, Honduras
http://srcopan.vze.com/

What you are most likely looking at in the handset, are more than
likely, the crystals for the local oscillators for the TX and RX. The
actual carrier frequency is a multiple of the crystal's fundemental
frequency.

A good way to know the actual frequency is to use a scanner to find it,
or for the best accuracy, use a spectrum analyser to see where it is.

If you go to any of the electronics parts suppliers that sell parts for
radio and TV servicing, they may have some whip antennas that will fit.
Most of these were very standard. If you cannot find one of the
quality, or proper matching, try any of the companies that sell
communications equipment.

--

These older type cordless phones usually worked in the 36 to 75 mHz
freqency band, depending on the country that it was to be sold in.

The newer 2.4 gHz phones are much more superior to what you have. The
new high end consumer phones are lighter, and can go farther.

Panasonic has a new line of them that is called the Gigarange. The
older Gigarange phones were at 2.5 gHz. The new ones are at 5.8 gHz.
This series can go very far.

An example of a few:
http://www.ahernstore.com/2linecordless.html

A friend of mine lives in the country. He has been about 1/2 mile from
his home with this 5.8 mHz phone, and it still works. With his
Gigarange, he can call out on his home phone, even if he is right
accross the lake.

I have take a 2.4 gHz up to several thousand feet from my home, and it
still worked.

Jerry G.
======

On Sat, 29 Jan 2005 17:09:32 -0600, Warren Post
wrote:

I´ve been given an old long range cordless telephone. The base station
takes two antennas (transmit and receive) but only came with the RX
antenna. I can make a homebrew TX antenna but need to know the
transmission frequency in order to do so.

Naturally the unit came with no manual, no specs, and no schematic. No
manufacturer´s name appears outside or inside the equipment, not even on
the PCBs. There are no FCC or UL numbers to look up. I do have a clue,
however: The base unit´s reception antenna is clearly labled ¨RX: 70
MHz¨. And inside the handheld unit there is a component stamped ¨70.365
H.ELE. CH23 1J¨. So 70.365 MHz seems to be the base unit´s RX frequency.
Also inside the handheld are two apparently identical commponents stamped
39.040 and 10.245 respectively. So perhaps one of these is the base
unit´s TX frequency in MHz?


70.365Mhz is the RX LO, (LO-IF=RF), so 59.665Mhz is the handset RX
frequency.
1st IF is 10.7Mhz, 2nd IF is 455 Khz. and therefore 10.245Mhz is 2nd
IF LO.

The handset transmits at 39.04 Mhz.

To test my idea I looked inside the base unit. There are four apparently
identical components, stamped 59.665, 10.245, 49.740, and ¨10M 15A¨,
respectively. So is it safe to conclude that 10.245 MHz is the base
unit´s TX frequency and that I should make the antenna for that frequency?


The freqencies are opposite to the handset.

49.740 is the RX LO, receives 39.040 Mhz, TX is 59.665Mhz. 2nd IF is
the as the handset.

Warren Post wrote:

The base unit´s reception antenna is clearly labled ¨RX: 70
MHz¨. And inside the handheld unit there is a component stamped 70.365.
So 70.365 MHz seems to be the base unit's RX frequency.
Also inside the handheld are two apparently identical commponents stamped
39.040 and 10.245 respectively. So perhaps one of these is the base
unit´s TX frequency in MHz?

To test my idea I looked inside the base unit. There are four apparently
identical components, stamped 59.665, 10.245, 49.740, and ????,
respectively. So is it safe to conclude that 10.245 MHz is the base
unit's TX frequency and that I should make the antenna for that frequency?

Warren-

I think you made a couple of wrong assumptions.

First, the most likely reason there are two antennas on the base unit, is to
provide "space diversity", so that when one antenna is in a bad spot, the other
is in a good spot. This overcomes fading caused by signals bouncing off of
walls and interfering with signals received directly. It is only necessary to
do it to one end of the link since it works both transmitting and receiving.

Second, the crystal frequencies are not necessarily the transmit or receive
frequencies. In a simple phone, one may be the transmit frequency, but the
ones used for receive are offset by an intermediate frequency (IF). In your
case, there are two IFs, 10.7 MHz and 455 KHz. A crystal oscillator mixes with
the received frequency to produce 10.7 MHz, the first IF. That signal is
amplified and mixed with 10.245 MHz to produce the difference, 0.455 MHz or 455
KHz, the second IF. The actual received frequency is probably one of the
crystal frequencies plus or minus 10.7 MHz.

I would guess that the handheld receive frequency is 39.04 plus 10.7 = 49.74
MHz. Note that one crystal on the base unit is 49.74 MHz. Receive frequency
in the base unit would be 59.665 plus 10.7 = 70.365 Mhz, which corresponds to a
crystal in the handheld unit.

Does this make sense?

Fred

On Sun, 30 Jan 2005 18:40:38 +0000, Fred McKenzie wrote:
the most likely reason there are two antennas on the base unit,
is to provide "space diversity"...

Point taken, although on this particular base unit the two antenna
connectors (male coax) are marked TX ANT and RX ANT respectively. I should
have made that clear in my original message.

I would guess that the handheld receive frequency is 39.04 plus 10.7 =
49.74 MHz. Note that one crystal on the base unit is 49.74 MHz. Receive
frequency in the base unit would be 59.665 plus 10.7 = 70.365 Mhz, which
corresponds to a crystal in the handheld unit.

Does this make sense?

Yes, so much so that I´m going to make a quarter wave whip antenna for
49.74 MHz and give it a try. Thanks!

--
Warren Post
Santa Rosa de Copán, Honduras
http://srcopan.vze.com/

Thank you, Fred. The base unit now works fine with a simple TX whip
antenna made for 49.74 MHz. I´m not getting the 1 km range I need, but
externally mounting the base´s antennas up high ought to fix that.

--
Warren Post
Santa Rosa de Copán, Honduras
http://srcopan.vze.com/