I've upgraded to an icom 718 , iy has a pre amp, typicaly useless but on the rare norning when I can turn on the pre amp and the static level is still low it can help. pre amp can be helpful, just not very often.typically zero noise without pre amp and 3-5 s units with pre amp, or greater.. doubt it will be much use on AM but. SSB, it can help. they are inexpensive but raising your antenna might be a better upgrade.
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internal CB preamps
- Thread starter Red Ranger
- Start date
The preamp in the 718 is within the AGC loop and keeps the noise blanker function exactly the same as it is when turned off.
HF hammm radio preamps are usually just the normal rf amp used on most superhet sets. They make it available to cut out to improve rejection of unwanted signals. This helps boost the radio's specs.
There are more then a few hamm sets that only use a mixer and no rf amp at all. The TS-440 is one of those. Squires Sanders SSR-1 was another.
tonight a buddy was mobil about thirty miles away. zero noise with pre amp off, pre amp on 5 s units of static but his signal was 9s units. the pre amp helped me hear him. weather the pre amp helps or not is something you need to try to figure out.
Receiver Preamps!
To be effective they " RX Preamps" first have to be located at the antenna end. Also they work best on antennas like beverage antennas, k9ay loops and flags etc. These antennas are receive only and very useful. If you run skip you know that the incoming signals change polarity moment to moment and having an ability to change receive antenna polarity is a must, and having antennas that work on the magnetics of the signal is where it is at. But this means in many cases a tuned preamp at the antenna. But there are times they do ok at the Radio end , but seldom, and only in certain band conditions.
73
Jimmy, WX9DX
To be effective they " RX Preamps" first have to be located at the antenna end. Also they work best on antennas like beverage antennas, k9ay loops and flags etc. These antennas are receive only and very useful. If you run skip you know that the incoming signals change polarity moment to moment and having an ability to change receive antenna polarity is a must, and having antennas that work on the magnetics of the signal is where it is at. But this means in many cases a tuned preamp at the antenna. But there are times they do ok at the Radio end , but seldom, and only in certain band conditions.
73
Jimmy, WX9DX
A preamplifier has no affect on signal polarity. It can only amplify a weak signal, so that may be what you are talking about there.
At HF a preamplifier certainly does not have to be at the antenna end of the feed line unless that feed line is the cause of a signal being weak. That's certainly possible at VHF/UHF and above but not HF in most cases (really terrible feed line).
The biggest liability with common preamplifiers is that they can not descriminate between wanted and unwanted signals, everything is treated the same.
- 'Doc
At HF a preamplifier certainly does not have to be at the antenna end of the feed line unless that feed line is the cause of a signal being weak. That's certainly possible at VHF/UHF and above but not HF in most cases (really terrible feed line).
The biggest liability with common preamplifiers is that they can not descriminate between wanted and unwanted signals, everything is treated the same.
- 'Doc
I second that on a proper alignment from a reputable tech. For example:Last year I sent in a NOS/NIB Royce 1-604 cb radio to DTB Radio for a basic tune. After getting it back I gave it to my brother as a gift. He thought that the receive sensitivity was cranked up too high,him having a few NOS/NIB radios himself but had never had them aligned by a tech but believed that all radios come aligned from the manufacturer. Also,I have a NOS/NIB GE 35 year old cb radio that had poor receive sensitivity. After tweaking the RX sensitivity I could then hear distant stations. A good performance properly set up base station antenna makes hearing distant stations a possibility.
I had one of those Bandit cb receive preamps decades ago. The RX signal could be attenuated as well as boosted. That worked in a mobile environment during quiet conditions. One more thing. Developing a good ear for listening to incoming signals is a bonus as long as the noise didn't overcome the RX signal.
Preamps, whether external or internal, are a complete and utter waste of time on HF. Unless your noise floor is S0, all that using a pre-amp does is make the signal to noise ratio worse making stations harder to copy. They don't make weak signals easier to copy, reducing gain does that.
Unless you live in the absolute arse end of nowhere preamps are of no use.
The noise floor for everyone, regardless of where they are is also above that of what the noise floor of the radio is, even standard un-tweaked. The standard 12dB SINAD figures quoted in the receiver specs are typically around -122dBm. At 12dB SINAD the received signal is still very clear. Galactic noise which is the dominant noise source you'll find on 27MHz in the quietest areas is around -121dBm. There is a chart from the ITU in the ARRL handbook. In short, weak signals are dominated by man made noise and using a pre-amp only makes the situation worse.
Here's some further reading.
ITU report.
Unless you live in the absolute arse end of nowhere preamps are of no use.
The noise floor for everyone, regardless of where they are is also above that of what the noise floor of the radio is, even standard un-tweaked. The standard 12dB SINAD figures quoted in the receiver specs are typically around -122dBm. At 12dB SINAD the received signal is still very clear. Galactic noise which is the dominant noise source you'll find on 27MHz in the quietest areas is around -121dBm. There is a chart from the ITU in the ARRL handbook. In short, weak signals are dominated by man made noise and using a pre-amp only makes the situation worse.
Here's some further reading.
ITU report.
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I learned to never use a CB preamp.
Many years ago a company built small preamps that were heat shrinked in a nice little package. All I can say is they worked....but maybe too good. Think I ended up removing the dozen or so I installed.
They kept coming back with the front end of the radio blown out. Every time someone would come by them with an amplifier on it over loaded their front ends.
I do run preamps today. But only on VHF weak signal and are mast mounted preamps from Research tech.
Many years ago a company built small preamps that were heat shrinked in a nice little package. All I can say is they worked....but maybe too good. Think I ended up removing the dozen or so I installed.
They kept coming back with the front end of the radio blown out. Every time someone would come by them with an amplifier on it over loaded their front ends.
I do run preamps today. But only on VHF weak signal and are mast mounted preamps from Research tech.
The ONLY time a preamp works is when there is NO noise on the band and that includes DX etc. They simply amplify the signal AND the noise by the same amount. In most cases with CB preamps the transistor used in the preamp has a higher noise floor than the radio's front end and as such actually degrades the weak signal ability of the system despite showing a higher signal strength. Preamps really show their merit on a quiet band such as is found on the VHF and UHF bands where there is no or very little man made noise to contend with.
Receive Preamps don't always increase noise without signal. I have one I bought online and it works great. It was not expensive and I didn't have to wait a month to get it. I bought mine on ebay here http://ebay.to/2owK8u1
I have seen other models called LiL Preamp but I don't know where to get them. There is another one you can build on CB Tricks. Also do a search on youtube for receive preamp. There is a good video of a home made one installed in a Cobra radio.
I have seen other models called LiL Preamp but I don't know where to get them. There is another one you can build on CB Tricks. Also do a search on youtube for receive preamp. There is a good video of a home made one installed in a Cobra radio.
While it is true you can design a preamp with filtering to do a stand up job it does not change the fact that just because you can not hear said station that they can hear you.
This hobby is based on talking to each other not listening to each other.
What most people really need is not a pre-amp but a method of filtering out the noise so they can hear the weak station over the noise. General rule of thumb is that if you can not hear them they can not hear you!
If you just want to hear distant stations we have another hobby for that sort of thing and we call that short wave radio and we use fairly small receive only radio's for that sort of thing!
This hobby is based on talking to each other not listening to each other.
What most people really need is not a pre-amp but a method of filtering out the noise so they can hear the weak station over the noise. General rule of thumb is that if you can not hear them they can not hear you!
If you just want to hear distant stations we have another hobby for that sort of thing and we call that short wave radio and we use fairly small receive only radio's for that sort of thing!
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