Re: [Discuss-gnuradio] Questions on rx_ofdm example in GR 3.7.1

[Martin Braun (CEL)]

On Tue, Sep 10, 2013 at 09:58:16PM +0000, Monahan-Mitchell, Tim wrote:
> GR 3.7.1
> gr-digital/examples/ofdm/rx_ofdm.grc
> 
> 1. The OFDM Frame Equalizer block that is downstream from the Header Stream 
> Virtual Source block has the Length Tag Key field set to length_tag_name, yet 
> all other blocks on the diagram with that field are set to length_tag_key 
> (which is the ID of a Variable block at the top of the diagram). Is that a 
> mistake? If someone will confirm, I can file the bug.

Hm. You make me look like a total scrub.

It seems you're right. However, on my machine, length_tag_name doesn't
throw an error. I just can't see why. GRC itself should figure this is a
problem.

> 2. When I try to run this flowgraph, modified for my target's custom source 
> block, I get this error:
> FATAL: Missing a required length tag on port 0 at item #0
> thread[thread-per-block[21]: <block ofdm_frame_equalizer_vcvc (22)>]: Missing 
> length tag.

That's good, actually -- it means your block is getting input, which
means it's receiving headers.

To be honest, the {rx,tx}_ofdm.grc files were more of an illustration of
how the OFDM chain works. I know I've used them successfully sometime in
the past, but I've changed some stuff in between.

Using the ofdm_tx and ofdm_rx hier blocks should, however, work. Can you
try those?

My main issues when transmitting OFDM is getting a clean spectrum. OFDM
doesn't like distortions at all.

MB

> Which led me to question (1) above. However, changing that block to match the 
> others does not correct the runtime error.
> 
> I found a couple of instances of the same error listed in (2) above in the 
> mailing list, but no one replied to them.

-- 
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