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OFDM750F issue

 

When selecting Mode OFDM750F I get a non-stop run of text characters across the screen that do not stop unless I select a different mode (such as OFDM500F or OFDM3500).?
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Why is this and is there a way to make it stop?
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Thanks.
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-Randy, W4IFI
 

Looks like the squelch does not have the desired effect with this modem. Dropping the squelch value for OFDM3500 has the same effect.
Robert
 
Edited

A further look indicates both OFDM500 and OFDM750 have this issue while OFDM3500 behaves correctly. On the initial modem switch squelch is operating correctly and as you decrease squelch level to below the noise level the series of random characters gets displayed. Increasing the squelch level to above noise level doesn't stop the random characters. Seems some code is missing for these modems that stop character display on a change to the squelch value.

Robert
 

There's definitely something not right with the way OFDM modes function in fldigi.? When I set fldigi to OFDM3500 centered at 1625 and send a message the station on the receiving end sees only gibberish text. This is using a 2 meter simplex freq. The sending and receiving stations can hear each others transmissions over the radio loud and clear.?
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When I try to change the center to 1375 the dashed lines in the waterfall do not move accordingly. And, the only way to change the center is to hover over the box and use the mouse wheel to change between 1375 and 1625. The arrows do not function.?
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The on going Saga of the OFDM modems, might be a good idea to just remove them until they get fixed, way to may issues. The PSK modems work well enough.

Robert
 

I agree Robert.? The?OFDM modes were introduced as experimental, and the original developer, John, KL4YFD, is not an active developer at this time.

David

On Wed, May 7, 2025 at 12:34?AM Robert, KK5VD via <kk5vd=[email protected]> wrote:
The on going Saga of the OFDM modems, might be a good idea to just remove them until they get fixed, way to may issues.? The PSK modems work well enough.

Robert
 

For those who have tried the OFDM modes, please note:
  1. designed to operate at a fixed audio center frequency
  2. DCD off not implemented, basically runs without squelch
  3. not suitable for HF communications
David


On Wed, May 7, 2025 at 8:32?AM w1hkj <w1hkj25@...> wrote:
I agree Robert.? The?OFDM modes were introduced as experimental, and the original developer, John, KL4YFD, is not an active developer at this time.

David

On Wed, May 7, 2025 at 12:34?AM Robert, KK5VD via <kk5vd=[email protected]> wrote:
The on going Saga of the OFDM modems, might be a good idea to just remove them until they get fixed, way to may issues.? The PSK modems work well enough.

Robert
 

The Pa NBEMS net extensively tested (a few years ago) the OFDM modes on 80m Sunday mornings 0730 hr.
OFDM500 was very frustrating and not very robust unless we had a very strong S/N.
The 80m NVIS paths did something to mess up decoding.
We compared OFDM to the much slower MFSK32 and THOR22/44/56 ?modes for traffic (FLMSG) and finally gave up on OFDM. Then the OFDM modes were dropped from Fldigi.
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I don¡¯t miss it on on HF SSB!
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However OFDM MODES did work extremely well on 2m/70cm FM.
But we found 8PSK500F and 8PSK1000F to be more robust.
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To what extent is OFDM like VARA?
Those of us who regularly use VARA HF and VARA FM are amazed at how well it copes with noise.
And¡­ VARA can adapt to changing conditions and change speed with no user input.
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That¡¯s like having a 20 speed bike on a mountain road compared to a single speed bike.
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I¡¯m curious what other ARES/RACES groups are finding as the ¡°best¡± (fast and robust) modes are on FM simplex and FM thru even an analog voice FM repeater? ?8PSK500F is my choice at this time.
MFSK128 for images.
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de k3eui barry
Philly
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