Anonymous wrote:
I need to replace the T/R relay on an FT480R.
(Intermittent Rx, curable by a quick blip on TX)

Are you sure the PLL locks when you go back to receive?

"gwatts" wrote in message
...
Anonymous wrote:
I need to replace the T/R relay on an FT480R.
(Intermittent Rx, curable by a quick blip on TX)

Are you sure the PLL locks when you go back to receive?

No reason the PLL frequency should change between TX and RX
as I'm only using it on FM simplex.

Another symptom is that the RX comes back on but
the squelch gradually becomes ineffective until you're listening to a
low-level noise and the squelch control is inoperative to cut it out.

The AF amp appears to be permanently powered at 13.8V so
my presumption is that I'm listening to an amp with no input.

In article , "Anonymous" wrote:

No reason the PLL frequency should change between TX and RX
as I'm only using it on FM simplex.

Just goes to show that YOU really don't understand the technology
that your dealing with...... Maybe a few courses in Modern
Radio Design, would help you understand how the PLL System
works in an FT480R.....

"You" wrote in message
...
In article , "Anonymous" wrote:
No reason the PLL frequency should change between TX and RX
as I'm only using it on FM simplex.
Just goes to show that YOU really don't understand the technology
that your dealing with...... Maybe a few courses in Modern
Radio Design, would help you understand how the PLL System
works in an FT480R.....

Which bits of it do you say that I don't understand?

Loop stability in control systems, perhaps? Lead/Lag
compensation? Triple loop PLLs to give 10Hz steps but
without the final loop stepping in 10Hz?

What exactly?

In article , "Anonymous" wrote:

"You" wrote in message
...
In article , "Anonymous" wrote:
No reason the PLL frequency should change between TX and RX
as I'm only using it on FM simplex.
Just goes to show that YOU really don't understand the technology
that your dealing with...... Maybe a few courses in Modern
Radio Design, would help you understand how the PLL System
works in an FT480R.....

Which bits of it do you say that I don't understand?

Loop stability in control systems, perhaps? Lead/Lag
compensation? Triple loop PLLs to give 10Hz steps but
without the final loop stepping in 10Hz?

What exactly?



It is the part where the PLL Frequency doesn't change because you
at using FM Simplex. There are many reasons for the PLL to change
between Tx and Rx, even with the radio in FM Simplex mode.

1. The receiver may have an IF Frequency of 10.7 Mhz which would
require the PLL to be offset from the Receive Frequncy by the
IF Frequency,
2. The Transmitter exciter may use a different Offset Frequency
than the Receiver IF Frequency, and most Transmitters don't
modulate the Tx Output Frequency directly, but modulate an
IF Frequency that is, either "mixed" to the Tx Frequency, or
"multiplied" to the Tx Frequency.

Just to name a few. Now Sir please, expound your brilliance on why
you made such a Stupid Comment in the Original Post, as sited
above...........

"You" wrote in message
...

It is the part where the PLL Frequency doesn't change because you
at using FM Simplex. There are many reasons for the PLL to change
between Tx and Rx, even with the radio in FM Simplex mode.

1. The receiver may have an IF Frequency of 10.7 Mhz which would
require the PLL to be offset from the Receive Frequncy by the
IF Frequency,

This is classic radio design, the vast majority of crystal controlled VHF
rigs from the seventies and eighties had a separete crystal for TX and RX
because of the IF stage in the receiver. Not true of all rigs though. The
FDK Multi 2000 as well as a PLL VFO has a number of crystal memories and has
a single crystal for each memory, but it's more the exception than the
rule - probably done to reduce cost of two crystals rather than one for each
channel.