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AM sensitivity

B

BobOnTheJob

My AM sensitivity is probably not what it could be. Icom IC-R1500 receiver with specs that show great sensitivity above 1.8mhz, but far lower sensitivity below 1.8mhz. What alerted me to the low sensitivity is getting a listenable signal at 130 miles from WLBH/Mattoon,IL 1170 on the 180' vertical longwire (S7 strength) yet barely being able to identify WLBH on the Wellbrook 1530 loop (S0 strength). Hooking a few feet of wire to the Icom produced a weak WLW at 90 miles, yet a couple feet of wire on a car radio brings in WSM at 230 miles. Bottom line...the $80 car radio is far more sensitive on AM than the $600 Icom. Is there a mod to "wake up" the Icom below 1.8mhz? If not, what's the consensus on an AM receiver that isn't deaf without a huge long wire?
 
I have an older ICOM ham rig (IC-745) that does the same thing. I never bothered about it because it's usually connected up to a large antenna anyway for ham radio use.

Have you thought of trying a tuned loop? I think that might do the trick without requiring a long wire.
 
audioguy said:
I have an older ICOM ham rig (IC-745) that does the same thing. I never bothered about it because it's usually connected up to a large antenna anyway for ham radio use.

Have you thought of trying a tuned loop? I think that might do the trick without requiring a long wire.
Click to expand...
Wonder why they do that? I already have the 180' long wire and the Wellbrook Loop (which I specifically acquired because it is broad-banded). The performance of the tuned loop is amazing, but having to tune it manually takes the fun out of it. Wonder if there's a receiver that doesn't suffer from this self-imposed sensitivity penalty?
 
Those are good radios for what they are intended but the issue is oscillator phase noise when you get that low. 25 uv sensitivity 500 to 1800 kilocycles but all the way down to 2.5 uv from 1.800 to 50 mc and that might be max at mid-band. Find you a Sony ICF-2002 much better down in the broadcast band.

w/
 
My old ham rig did the same thing actually had reduced selectivity below 1500. There was supposedly a mod to change that but I never tried it
 
Most ham rigs have considerably more RF amplification above 1600 khz. My understanding is that the sensitivity on these rigs below 1600 khz is intentially reduced to alleviate overloading of Broadcast stations which are usually more numerous, use wider Amplitude Modulation and generally operate with much more powerful than most ham stations. If the same receiving specs were used in the AM band, overloading would be intolerable, especially in larger metro areas where many stations operate. I have several ham rigs which do this, but with a long-wire receiving antenna, they still are pretty sensitive for BCB DXing.
 
KR4BD said:
Most ham rigs have considerably more RF amplification above 1600 khz. My understanding is that the sensitivity on these rigs below 1600 khz is intentially reduced to alleviate overloading of Broadcast stations which are usually more numerous, use wider Amplitude Modulation and generally operate with much more powerful than most ham stations. If the same receiving specs were used in the AM band, overloading would be intolerable, especially in larger metro areas where many stations operate. I have several ham rigs which do this, but with a long-wire receiving antenna, they still are pretty sensitive for BCB DXing.
Click to expand...
Point well taken, but most of these receivers have attenuators on the front panel...don't they think hams are smart enough to use them? With a long wire, the sensitivity is fine, with the amplified Wellbrook 1530 loop (a quite expensive antenna by the time you ship it from Europe), the sensitivity has quite a bit of room for improvement.
 
Has anyone used a preamp with the Wellbrook active loop antenna? If so, what model of preamp & what were the results? It seems apparent that all non-portable AM receivers suffer from this self inflicted sensitivity wound.
 
Not with the Wellbrook, but a 1925 vertically-squashed loop. Think of an elongated hexagon. That part is rotatable, and reasonated
with a 1930 Crosley "book" capacitor. Inside and loose coupled ( variably by angle) is about 4 loops to the actual output.
That I feed into an MFJ noise-cancelling antenna amplifier, (as the noise signal) and turn the gain up.
Feed that into my Collins 390A which which is getting kinda weak on 1 Mhz range.
Well, actually now it's asleep awaiting diagnosis after eating some 26Z5s..... Probably main filter caps.

Did it wake things up? A lot. If you've ever played with a Q amplifer it's a lot like that in effect.

The Sangean 803 ATS is just the opposite ,sensitivity is pretty hot off the built-in loop up to 1620, then WAY down on the whip
at 1621. Always wished it had a switch instead, but I understand the limitations of the varactor capacitor step-tuning in a
non-hardware radio. :mad:
 
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