AT-778UV Mixed Emotions

[HomerBB]

A fellow once said he had mixed emotions. His mother in law had driven his new pickup truck over a cliff...

There isn't anything about this radio for the money I didn't like, until...
I put a Tram 1481 antenna up (it was a gift) increasing my tx/rx range over the smaller verticals I'd been using. Now I get intermod on 2m so severely it wipes out my receive rendering the radio useless.
I can prevent this by moving the radio from wide band to narrow, but it lowers performance with other radios in the area. We have a very active 2m/70cm ham community here, esp at 146.520.
My Icom, a TYT HT, and old Kenwood TM-261 do not experience this issue.

 

[sp5it]

You need a bandpass filter or FM trap.
Mike

 

[HomerBB]

You need a bandpass filter or FM trap.
Mike

When I look at these I become confused about which to get. They seem to be worthless when they are receive only... shows what I don't know.
I just wish it had the rejection the other radios are/were equipped with.

 

[sp5it]

First I would get cheap filter for SDR to check if it gonna work for you.
Than https://www.antennas-amplifiers.com/2-meter-bandpass-filter-transmitting-100w if cheap one helped with out of the band signals.
Mike

 

[Handy Andy]

A lot of these are SMD so to use a simple "install here" filter - makes this more of an OEM trick than to simply offer a drop-in solution you could solder in.

The 2M inter-mod problem is common when you use a higher gain antenna - does nothing for the SELECTIVITY of the unit in question - it's a reciprocal (give me this, you get that in return) sort of event - higher gain for weaker signals but bring more Garbage from what the previous antenna tended to suppress (Or ignore)

Now are you sure you can blame the inter-mod on 2M and not just overload form a commercial station that just happens to be smack-dab on a harmonic?

Would like to see the schematics or any type of kit installs if any from OEM - to help...

 

[HomerBB]

I am not sure of the source, except it gets worse as I go up the 2m band from 146 MHZ. I'm going to park in the 152/153 MHZ are and see what happens.

 

[Handy Andy]

Well, what would help is to know - by sound of, what TYPE of inter-mod you're getting could be a strong clue as to what or kind of source it is.

Constant or choppy, or sounds like "Digital" are potential methods of carrier/emission but doesn't say much about where or how the noise is generated.

Some Inter-mod may not be from higher regions - it may come from harmonics produced in the bands BELOW yours'

To add:

The problem with external band pass filtering is it lets thru what is in the band, but does not rule out mixing products achieved from the inter-mod itself

So if your radio is seeking a signal from a local - but is fighting an incoming signal from the FM commercial below you, then the operator keys up - you're fighting the inter-mod at your radio, not thru the airwaves. a 10MHz difference is an IF issue.

What can also happen is from the other local stations doing PSK or RTTY or Slo-Vid - they may wind up producing the carrier that allows even an AM station to ride in and you're hearing News WX and the latest Sports from the inter-mod generated not at your radio, but thru the simple mixing products occurring in the RF amp that don't get rejected but can be tamed by simply using an internal filter for this instead.

 

[HomerBB]

And there's the rub. Apparently it does not have sufficient internal filtering, and I am not the fellow a person wants looking inside a radio.
On a Baojie BJ-218 it sounds like the NOAA weather bleeding in.
Here's what I'm getting on the AT-778UV.

https://youtube.com/shorts/XliCvhrU4Js?feature=share

 

[Handy Andy]

Every now and then a hear a "bloop" like a EOT/PSK_END or a Dispatcher's unkey and the repeater "opens" for the return call. Could also be from a PC - but you don't get "bloop" - you just get noise.

So that is a commercial or other business operation that is using some kind of repeater, or a dispatch using a "roger beep" to end transmission.

Considering the noise also brought in, this is an image - not from the external - which isn't helping, but an image from the processing going on in the radio.

I feel your pain and I wish I could help more - but you're in a realm of warranty and returns that I do not wish to stand in the way of.

I would (and am, in a way) frustrated like you that foreign builders let this stuff get sold and then you're left wondering "If it's so great - why can't I hear my wife calling?"

 

[HomerBB]

I will try it in the mobile and see how it goes. Maybe with a lower gain antenna I'll hear less mess.