SAM mode and beat note.

George M.

As you know having SAM node on while in a QSO with stations off frequency causes beat note while locking onto their carrier. Is there anyway of blocking the beat note while this is in "Action"? It can get very annoying after awhile both constantly asking the station to center their frequency and the beat note zeroing tone. Can't hear anything while this is in progress too so the first part of the conversation gets lost.

James Del Principe

I can appreciate what you are saying.  SAM is both a blessing and a curse.  In the not too distant past, SAM was very difficult to implement, but with the technology of the Flex, it is possible. I use it every morning on an AM roundtable. People with boat anchors are usually off from a few hundred cycles to a KC or more. In the past, this was as good as it got with analog dials and antique modulation. Receivers were broad enough so it did not make a difference. I'm not sure if there is a solution except to get everyone on frequency or just use AM and not SAM.    73, Jim

KF4HR

Why not create a TNF to eliminate the beat note?

Jack6600

SAM is very similar to AFC in an FM radio and is nothing more than a PLL system. I would think that if another station keyed up off frequency and if the frequency is within lock range of the SAM, it should obtain a fast lock. There are cases where it might take a few seconds to lock.  I found that you can increase the bandwidth a bit and widen the lock range. But be careful. If there’s a nearby carrier or SSB, SAM will phase lock to it.  

Lionel

SAM would be better if the time to lock could be decreased. I know there are trade offs in PLL design but, is it possible? Perhaps this would decrease lock range, or have other effects, but I don’t know enough to suggest the trade offs.

James Del Principe

Lionel, I use SAM every morning for an AM roundtable. Most use boatanchors so their carriers are all over the map. I agree it could be better but I wonder what release you are using. This is subjective but I think it is improved at release 3 which I am running... or maybe just the placebo effect. 73, Jim KD1I

Lionel

Jim,

I'm using 2.6.2 but have not tried to quantify the time to lock. Maybe I can figure out how to measure the time.

James Del Principe

Lionel, I use SAM every morning for an AM roundtable. Most use boatanchors so their carriers are all over the map. I agree it could be better but I wonder what release you are using. This is subjective but I think it is improved at release 3 which I am running... or maybe just the placebo effect. 73, Jim KD1I

Lionel, the time will vary depending on 1. the degree of transition and 2. if the SAM had adjusted in one direction for a given signal and then in another direction for the next signal. I long for the days of crystal control. HI HI

Bill N3HQB

The time to lock in on SAM varies from SDR to SDR, suggesting that some improvement could be possible.

The audio quality in SAM is vastly better than AM, except for the time it takes to lock onto a carrier and zero beat.

James Del Principe

Bill, do you mean among a given SDR such as one 6500 compared to another 6500, or do you mean different SDR radios, perhaps different models or different manufacturers?

As for audio quality, I think that is true under weak signal conditions but it should not matter for a signal with a strong carrier. 73, Jim

Lionel

I'd think that between 6500's or 6400's etc the behavior would be similar. I'm listening to 3825 and three or four in qso. They're using Flex, sooo, they are all on same frequency. (1511z in MN)

One guy came in briefly at about 2 khc up and sync'd in a second or two; pretty fast, but annoying. If multiple BA users, it would be a better test.

Lionel

Update - I looked closer.

With an AM group on 3825 (8Khz BW - SAM) a station at 3825.852 took over one second to sync. Unfortunately I only have one data point.

If I change my rx frequency SAM follows perfectly. But if the sync'd carrier drops, the off frequency carrier sync's (re-sync's??) at an obvious rate.

Also, the signal strength has an effect on sync time, or so it seems with my decidedly unscientific methods.

With and 8 khz BW SAM syncs with rx frequency offset 4 khz (3825 to 3829) without any obvious time delay as long as all stations are on 3825.000.

Science project!

Bill N3HQB

Jim, I was referring to different SDR manufacturers.

My 6300 does reasonably well, but occasionally when another op makes a very short transmission, he's finished before the SAM sync locks.

W4OP

I am a new owner of a 6400M. I see no real difference between AM and SAM. In SAM as I tune across an AM station, there is no beat note heard and there is never any change in frequency indicating an attempt to lock. SW ver. 3.3.32.8203

Tnx,
Dale