148 vs Export Radio - Why?

[Ace_King_21]

Heres the "subjective" specs direct from the manufactures

Ranger 2980wx
AM / CW: 0.7 µV for 10 db SINAD - Not as good as the 148
SSB .2 uv for 10db SINAD - About the Same as the 148
Spurious Emission - More Than 60 dB - Better than the 148
IF Rejection More than 80 db at 455 KHz Not nearly as good as the 148
Carrier Suppression More than 60db Better than the 148
No AGC Spec given
Image Rejection - "More than" 50db - This sucks the 148 is way better
Skirt Selectivity
AM / FM Selectivity - 50 db at 10 KHz - No 6db figure given -148 better
SSB Selectivity - 5 db at 2 KHz, 60 db at 4 KHz - Sloppy, Sloppy, Sloppy

Cobra 148
AM 0.5uV for 10 db SINAD
SSB 0.25 uV for 10 db SINAD
Spurious Emission - -55bd
IF Rejection - 100db @ 455khz
AGC - Less than 10db change in audio output from 5uv to 50,000uv.
Image Rejection - 75db
Selectivity
AM: 6dB @ 3 KHz, 50 dB @ 9 KHz.
SSB: 6 dB @ 1.1 KHz, 60 dB @ 2.3 KHz

The 2980 vs 148 - What kills me is the image rejection and skirt selectivity. This is why I am weary of an export. Most of them have these very same specs or similar. But the price tag aint nearly the same.
It appears to be true that the freq counters in many exports is reading only one of the signals in the radio, that seems to leave alot of room for an inaccurate reading.

 

[222DBFL]

There are actually a few export radios that can track both TX/RX, and have basically a true RIT. The microprocessors tend to keep these radios on frequency better than the old radios. I am not a tech, so don't flame me. But I do know that some of the new export radios aren't that bad and there are a couple that actually kick butt! The Optima MK3, no longer in production, is one awesome SSB radio. Not the best on AM, but it was geared more toward SSB use IMO, and it shows when you are on SSB. Tuning into freq is not that hard if you have decent hearing and know what people sound like normally. There are so many HF radios being used these days even on 11m SSB that it's not too hard to find someone on freq and tune to them. Or have a monitor radio.
Radios like the strkyer 955hp actually do show the last 2 digits and allow for fine tuning of the clarifier I beleive. Someone that owns one of them will know.
I do understand the hesitation to get an expensive export radio, maybe think along the lines of a kenwood 480HX. 200w SSB and they do pretty darn good on AM as well. And you won't have any drift issues with it. But we are talking exports and CB's here, so idk if this is something you may or may not have thought about. At any rate, good day and enjoy those old radios! A lot of them work very well and I actually have a couple myself that I have kept over the years.
Anyways, again, have a good day.

 

[undertaker]

Cant beat a 2950dx.....

 

[Steve_Buckeye]

You can find a good export radio for about $300 pushing 80 watts or so. More money for higher output! A 148 is a great 30 year old radio, by the time you have it recapped aligned, etc it will cost you about $500 for 4 watts output. Unless you are the tech, its cheaper to get the export. If you are talking about a new 148, China model, you need to spend another $100 for the mods and alignment and still give only 4 watts. RM Italy has a cheap KM-203 amp $80 for 80 watts. So do the math.

 

[Tallman]

You can find a good export radio for about $300 pushing 80 watts or so. More money for higher output! A 148 is a great 30 year old radio, by the time you have it recapped aligned, etc it will cost you about $500 for 4 watts output. Unless you are the tech, its cheaper to get the export. If you are talking about a new 148, China model, you need to spend another $100 for the mods and alignment and still give only 4 watts. RM Italy has a cheap KM-203 amp $80 for 80 watts. So do the math.

Plus you still won't have the extras that come with a good quality ham radios. Such as notch filters, adjustable AGC, and so on.
Also some of those specifications were a bit misleading on the SSB. Notice the modulation frequencies are different between the two so the results will be different. I would like to see what would happen if the test conditions were the same.

2980wx
SSB Selectivity - 5 db at 2 KHz, 60 db at 4 KHz

Cobra 148
SSB: 6 dB @ 1.1 KHz, 60 dB @ 2.3 KHz

 

[Old_Crow]

Nothing like my old 148, its day are numbered, II will be very sad when she blows.

 

[Ace_King_21]

So much good information here. Thanks to all who responded with useful 411 and not being drunk behaving like children and cussing at people.

Anyway ..
Tallman the specs you referenced are for the RX filter not the TX bandwidth ?.. i must have not been clear. At least thats what I think looking at the specs.
I believe the spec refers to the shape factor of the filter
That, according to many intellectual books on radio, definition indicates the degree to which the real filter differs from the ideal". - Shape Factor
To calculate the S.F. just divide the bigger number by the smaller. the closer to 1 the better.
2980 Shape Factor Calculation
4/2 = 2
148
2.3/1.1=2.09
The 2980 spec starts at -5db and the 148 at -6db. It was unpublished on the Ranger site the spec at -6db. Makes me wonder why Ranger would vary away from the "Normal" spec's. My guess, is the shape factor is more than 2.
Again, according to real radio books, a shape factor of 2 or more is a the very bottom end of performance.

Referring to the BW of the filter with can be calculated using the formula:
Bw=Fr/q

Where
BW = bandwidth at -3db ponts
Fr =resonant frequency
Q= selectivity factor

2980

Audio bandwidth - 300hz - 2500hz
Upper and Lower sideband separated by 600 (2x300(lowest audio frequency passed))
IF Frequency 10.695

Q=Fr/BW
10.695mhz/600hz=17825

The problem is the -60db point on the 2980 is +/- 4khz - thats wide enough to pass 2 ssb conversions!! Far to wide to provide good adjacent channel rejection which appears as poor receiver selectivity.

148

7.8mhz/600 = 13000

It may seem, at first, the rci with a filter Q of 17,825 is better but not so

The -60 db is 2.3 khz which is only wide enough to fit 1 channel - this makes the 148 filter superior to the RCI export and appears as good selectivity and adjacent channel rejection.



The 148-GTL DX has even better performance

-6db 2.1khz
-60 db 3.3 khz

Filter Q = 17825 - Same as the RCI 2980

3.3/2.1 = 1.57

These are nice specs.


One can use this information to determine how cheap the manufactures of CB type radios are. As an example:

Uniden Washington (8719 pll)

The spec

-6db 4.2 -60db 7.9

7.9/4.2 = 1.88
Q= 7.8/600=13000

Its obvious that this a single conversion receiver that gets it's selectivity from the IF filter - shared by SSB and AM - Thats wide enough to pass a full DSB signal + a bit more.

When I see -6 db at more than 3.0 khz if makes me worry that the receiver is compromise - and in this case it is. What other reason would there need to be to have a filter wider than the incoming signal? To me thats like trying to filter dust with chicken wire fencing.

Thanks to ALL , I hope I got this right.

After all this investigation - A nice Kenwood does seem like a viable option.

 

[Tallman]

After all this investigation - A nice Kenwood does seem like a viable option.

I like Kenwood equipment I have four of them also two Yaesu and three Icom radios.
I wasn't trying to rattle your cage but filters can have have wildly different characteristics. The test inputs were different enough to question.

 

[Ace_King_21]

No cage considered rattled!! Actually, every post with the exception of a few, I have researched. From the Stryker, Magnum S-9, RCI and 148 cb version and the DX version. i do feel an affinity to the 148DX

May I ask which manufacture you prefer? As in Kenwood, Icom or Yeasu?
I do like that Kenwood 850 ,price isn't bad for what it can do.

Im not looking for the cheapest radio but one that has the most performance / dollar.

Even more specifically the RX performance. Theres a million mods for increased TX performance but not so many for RX.





thanks for your time and expertise

 

[Ace_King_21]

And Mr Old Crow

I can tell u love your 148!!! I hope it never breaks on ya!!!

 

[Tallman]

May I ask which manufacture you prefer? As in Kenwood, Icom or Yeasu?
I do like that Kenwood 850 ,price isn't bad for what it can do.
Im not looking for the cheapest radio but one that has the most performance / dollar.

My favorite radio is my Icom 7100. I bought seven "Ham Sticks" antennas because I use it as a mobile in my truck. I have individual antennas for 6, 10, 15, 17, 20, 40, and 75 meter bands. I use the 40 meter for 80 meters and have a MFJ antenna tuner inside the cab. For good measure I also run a Uniden 980 SSB for CB while on the road.
I also have the Antron ADB-270 for two meter and 70 cm bands. This radio covers a huge amount of frequencies.

 

[Ace_King_21]

Nice..just looked it up...lots of stuff on that baby!!!

Love the SSB Filter - That must sound fantastic.

Thanks Again, Tallman!! Your input to my post does make a difference to me and my decisions.

I'm obliged to you.

 

[Ace_King_21]

Undertaker - Thanks for the 2950 recommendation, it does seem like a good radio if you can get a square price for it!!!

 

[Tallman]

Nice..just looked it up...lots of stuff on that baby!!!

Love the SSB Filter - That must sound fantastic.

Thanks Again, Tallman!! Your input to my post does make a difference to me and my decisions.

I'm obliged to you.

It does need an external speaker though. The factory speaker is mounted in the control head and directs the sound away from you.

 

[9C1Driver]

I am wondering why people like export 10 meter radios so much? I mean the specs for a 148 are as good or better than many of the so called high end export.

any truck stop can add freq's to the 148 and a two pill amp makes it an export.

some how robot voice and echo/echo depth knobs don't really seem like real adjustments.

So my question is why spend 400+ on a radio when a slightly modded 148 will be the same as a
very expensive export?

My base radio is a Uniden Madison with channels, I love it. I also have a Magnum Delta Force, 257HP, and S45HP, they are all great radio's. I like tha fact that they are processor controlled, 12 bands of channels, FM, echo, talkback, they scan, split channels. That's my reasons. Love the old Uniden Grant xl too.