BC125AT Frequency coverage

[KD4UXQ]

According to the manual the BC125AT will not cover 380-399.975 MHZ portion of the Military UHF band.
I was considering getting one to supplement some of my Mil Air monitoring, but if this is true then it will not meet my needs and sadly the needs of others that have the opportunity to monitor Mil Air in this range.

380-400 MHz is not used solely for Trunking. There are still command posts and discrete Mil Air channels in this range. Not many, but definitely there!

If this is this case it is a flawed assumption by the designer that the range has been hard assigned for trunking. This is reminiscent of the past older models that did not follow the band plans correctly, channel steps and all modulation methods used in the bands.

Can someone confirm this that owns one?

If true then it should be rectified.

 

[737mech]

According to the manual the BC125AT will not cover 380-399.975 MHZ portion of the Military UHF band.
I was considering getting one to supplement some of my Mil Air monitoring, but if this is true then it will not meet my needs and sadly the needs of others that have the opportunity to monitor Mil Air in this range.

380-400 MHz is not used solely for Trunking. There are still command posts and discrete Mil Air channels in this range. Not many, but definitely there!

If this is this case it is a flawed assumption by the designer that the range has been hard assigned for trunking. This is reminiscent of the past older models that did not follow the band plans correctly, channel steps and all modulation methods used in the bands.

Can someone confirm this that owns one?

If true then it should be rectified.

Confirmed. No coverage 380-400.

 

[KD4UXQ]

Confirmed. No coverage 380-400.

Thanks for the confirmation.

Sad. A really bad oversight by Uniden. It would be like not allowing AM from 148-150 because it is mainly used for FM mode with Land Mobile, but sometimes used for Mil Air in AM mode.

 

[nanZor]

My thought is that since this is a triple-conversion scanner, the first IF may be in the 380-400 range, and operations here would be pretty poor due to bad IF rejection, but also odd-order harmonics from the 2nd and 3rd IF's raising the noise floor. So perhaps 380-400 is a good no-man's land to protect the first IF stage unless there was more exten$ive filtering.

It's just a guess though - GRE's PSR500/Pro106/Pro197 use a first IF of 380.8 mhz, 21.4 mhz for the 2nd, and 455khz for the 3rd. Kudos to them for publishing this information.

Uniden's IF frequencies may be similar. However, the RS models DO have coverage in this range, but it would be interesting to get feedback from users monitoring 380-400 with them to see if the scanners are actually usable, or are just totally deaf in this range.

For some strange reason, I don't think it was an oversight, but a technical decision. But I could be wrong.

 

[W8RMH]

This was brought up before and I think UPMAN had a reply, but I can't locate the thread. There was some technical reason for it I believe.

If you got the time to go through all the threads you may find your answer.

BC125AT Threads

 

[GTR8000]

Paul's post regarding 380-400:

http://forums.radioreference.com/un...5at-new-scanner-announcement.html#post1645123

 

[KD4UXQ]

Paul's post regarding 380-400:

http://forums.radioreference.com/un...5at-new-scanner-announcement.html#post1645123

Paul's assumption in that post is certainly not correct.
"Since 380-400 is primarily trunked and primarily digital (actually, according to the military's current frequency plan, there should be no air traffic in 380-400), the need to lose this segment for other considerations was acceptable (since in practical use, it is eliminating a band in which there is nothing to hear with an analog, non-trunked scanner)."


None of the military bands should ever be considered as hard set for usage. Frequency management in the military bands is handled by numerous frequency managers. There are particular operations that are dedicated to certain frequencies, but not necessarily to specific segments of any band. Anything not in use by trunked systems in the 380-400 MHz segment may very well be used for aircraft communications in AM mode.

 

[KD4UXQ]

BTW

Shaw AFB Command Post is still on 381.3. I haven't been to an Airshow there in a few years, but it is still listed as 381.3 on Airnav.com. Just a quick look shows Tinker AFB AFMC Flight Test still on 382.6.
Cherry Point CAMEL BASE: 383.4 . Seymour Johnson AFB RAYMOND 25: 381.3 .

I recently monitored USCG SAR on 381.8 on a trip to Florida last year.

 

[KD4UXQ]

My thought is that since this is a triple-conversion scanner, the first IF may be in the 380-400 range, and operations here would be pretty poor due to bad IF rejection, but also odd-order harmonics from the 2nd and 3rd IF's raising the noise floor. So perhaps 380-400 is a good no-man's land to protect the first IF stage unless there was more exten$ive filtering.

It's just a guess though - GRE's PSR500/Pro106/Pro197 use a first IF of 380.8 mhz, 21.4 mhz for the 2nd, and 455khz for the 3rd. Kudos to them for publishing this information.

Uniden's IF frequencies may be similar. However, the RS models DO have coverage in this range, but it would be interesting to get feedback from users monitoring 380-400 with them to see if the scanners are actually usable, or are just totally deaf in this range.

For some strange reason, I don't think it was an oversight, but a technical decision. But I could be wrong.

You may be right about the first IF. I suspect you are correct. Certainly possible, but it would still be better to include the range and publish the IF frequencies instead of killing an entire 20MHz segment that can likely be used for Aircraft comms. I doubt it is the front end filtering since it does cover 400-512. The BC125AT may well be a fine radio but I would be reluctant to recommend it for Military Aircraft comms.

 

[KD4UXQ]

Paul's post regarding 380-400:

http://forums.radioreference.com/un...5at-new-scanner-announcement.html#post1645123

BTW

Thanks for digging that up.

 

[nanZor]

Although there is still activity in your area on 381.3, I think the other 155 mhz of milair spectrum it does cover is a very good value and still worth considering especially for it's price range. They could have dropped milair entirely and it would still sell ok - I'm glad they didn't and see it as a value-added feature personally.

Prior to the 125, the only way to get any milair at all with Uniden was to pay 4-5 times the price for a 396/996 and become familiar with the DMA programming - or drop to the simpler, less portable 370/345 CRS clock radio systems - which still blows my mind btw!

I've got a feeling that the "other considerations" might have led eventually to NO inclusion of milair at all, so I'm thankful for the 155mhz spread we've got.

 

[GTR8000]

Maybe Paul can expand on this if he sees fit, but it's worth noting that some of the newer Uniden scanners have two first-stage IF crystals. That's how the IF Exchange function works, and also allows them to cover the 380 spectrum cleanly as it switches automatically when it's in that band.

I don't have the specs for what IF frequencies Uniden uses in the XT series or HP-1, but here's what the Radio Shack PRO-160 uses, a scanner that was built by Uniden Japan, not GRE. I suspect it's the same or very similar in the rest of Uniden's mid to high range triple-conversion scanners:

IF Frequencies .....265.55/380.75 MHz, 10.80 MHz, 450 kHz

Note that the first IF stage uses either 265.55 or 380.75. There is no IF Exchange function on this model, it simply switches IF automatically depending on the band it's working in. Obviously if you're monitoring 380 MHz, it's using the 265.55 MHz IF.

I don't know whether the BC125AT has a single or dual first-stage IF, and if that had any impact on the decision to omit 380-400.

 

[KD4UXQ]

Although there is still activity in your area on 381.3, I think the other 155 mhz of milair spectrum it does cover is a very good value and still worth considering especially for it's price range. They could have dropped milair entirely and it would still sell ok - I'm glad they didn't and see it as a value-added feature personally.

Prior to the 125, the only way to get any milair at all with Uniden was to pay 4-5 times the price for a 396/996 and become familiar with the DMA programming - or drop to the simpler, less portable 370/345 CRS clock radio systems - which still blows my mind btw!

I've got a feeling that the "other considerations" might have led eventually to NO inclusion of milair at all, so I'm thankful for the 155mhz spread we've got.

Good point considering it's price, but the reasoning for not including based on there should not be any Mil Air comms in the range is completely incorrect. Unfortunately it's not a good choice for me and it certainly shouldn't be considered as a good option for Mil Air, but rather for everythiung else it covers and, by the way it covers a portion of the Mil Air band.

 

[KD4UXQ]

Maybe Paul can expand on this if he sees fit, but it's worth noting that some of the newer Uniden scanners have two first-stage IF crystals. That's how the IF Exchange function works, and also allows them to cover the 380 spectrum cleanly as it switches automatically when it's in that band.

I don't have the specs for what IF frequencies Uniden uses in the XT series or HP-1, but here's what the Radio Shack PRO-160 uses, a scanner that was built by Uniden Japan, not GRE. I suspect it's the same or very similar in the rest of Uniden's mid to high range triple-conversion scanners:

IF Frequencies .....265.55/380.75 MHz, 10.80 MHz, 450 kHz

Note that the first IF stage uses either 265.55 or 380.75. There is no IF Exchange function on this model, it simply switches IF automatically depending on the band it's working in. Obviously if you're monitoring 380 MHz, it's using the 265.55 MHz IF.

I don't know whether the BC125AT has a single or dual first-stage IF, and if that had any impact on the decision to omit 380-400.

I would bet the Unidens use the same IF scheme as well and the BC125AT being a less expensive model has only one 1st IF option as you suggest. Multiple or variable 1st IF frequencies are the best way to cover a large range and avoid internal products that get fed back into the receiver. I had sort of forgotten this was the case and certainly is one some wide range commercioal rack mount receivers I worked with in the past. That was quite a few years ago and I hadn't remembered it until you posted this.