On Jun 26, 11:34*am, wrote:
On Jun 26, 3:32*am, Paul Keinanen wrote:
why would anyone use the receiver CW filters

Probably a bit narrower than what I had in mind … *I'm currently
looking
at 500 KHz wide SAW filters.

As a rough guesstimate, the group delay in a 500kHz wide filter will
be 1/500,000 secs, or 2.0 microseconds. Now, depending on shoulder
steepness the change in group delay might get to 2, 3, maybe even 5
times 2.0 microseconds. But even at 20 microseconds I don't think any
of the HF digital modes you mentioned would be impacted.

Most of my comments regarding group delay and ringing in filters were
oriented towards narrowish (few kHz or less) filters.

Wow, a HF receiver with a 500kHz SAW filter after the mixer. I don't
have a clue what you're doing! I thought we were talking about HF
receivers for common bandwidths!

Tim N3QE

On Jun 26, 2:40*pm, Tim Shoppa wrote:
But even at 20 microseconds I don't think any of the HF digital modes you
mentioned would be impacted.

Thanks ... that's the type of information I was curious about.

Wow, a HF receiver with a 500kHz SAW filter after the mixer. I don't
have a clue what you're doing!

I'm "playing" with something resembling 0 - 175 Mhz up converted to
208 Mhz
filtered using a GSM SAW filter sampled at the first IF using a 25
Msps 16 bit
ADC. The silly width is because I'm interested in handling broadcast
FM
including RDS (among other things). I'm also interested in receiving
satellite
images which in some cases has a bandwidth of 150 Khz.

-- John

As another random datapoint there's a
MetOp document regarding the LRPT satellite
transmissions which says:

Frequency range Group delay
(kHz) variation (ìs)
[0-40] +/- 2
[40-60] +/- 5

-- John

[Let's try this again ... that should be microseconds (us) not (is)]

As another random datapoint there's a
MetOp document regarding the LRPT satellite
transmissions which says:

Frequency range * * * Group delay
(kHz) * * * * * * * * * * * *variation (us)
[0-40] * * * * * * * * * * * *+/- 2
[40-60] * * * * * * * * * * *+/- 5

-- John