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For a listener, a transmatch has something of a similar nature - it can help create a resonant path between the radio and the antenna system (we'll get to that in a moment) and improving the efficiency.
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For a listener, a transmatch matches the impedance of an antenna to the impedance expected by the receiver. This allows energy to be transferred from the antenna and feedline to the radio, increasing the receive efficiency of the antenna.
 
 
 
 
Why an 'antenna system'?. Keep in mind that with a transmatch, you are not just tuning the antenna, but in some cases (depending on the antenna design), the feedline as well. Here is the basic different between a true antenna tuner and a transmatch. Recall that a true antenna tuner is placed at the '''feedpoint''' - therefore, it does not tune the feedline. A transmatch might need to tune the feedline, and is usually placed at the '''shack location''', close to the receiver.
 
  
  
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* Pi network tuner
 
* Pi network tuner
 
* L Tuner
 
* L Tuner
* T Tuner
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* Tee section Tuner
 
* Z Match Tuner
 
* Z Match Tuner
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Here are a couple of homebrewed solutions
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* [http://www.hard-core-dx.com/nordicdx/antenna/special/2010ant.html Build Your Own Antenna Matching Device - Improve Sony 2010 Reception]
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* [http://www.hard-core-dx.com/nordicdx/antenna/lab/tuner.html Homebrew Simple Antenna Tuner]
  
  
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It's important to evaluate if a filter will solve your problem before you buy it. The better ones have a response curve that will show you how the filter attenuates at different frequencies. A practical example would be something like this; you have a FM broadcaster at 100.3 Mhz that overloads your radio. The unit you are looking at has a response curve that shows attenuation doesn't start until 101 Mhz. Therefore this filter would be largely ineffective in blocking the 100.3 broadcaster. See the FM filter from PAR electronics link for an example of a response curve diagram.
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It's important to evaluate if a filter will solve your problem before you buy it. The better ones have a response curve that will show you how the filter attenuates at different frequencies. A practical example would be something like this; you have a FM broadcaster at 100.3 Mhz that overloads your radio. The unit you are looking at has a response curve that shows attenuation doesn't start until 101 Mhz. Therefore this filter would be largely ineffective in blocking the 100.3 broadcaster. See the filters from PAR electronics and ICE for examples of a response curve diagram.
  
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* [http://www.dlwc.com/ DLW Associates BCB Reject Brick Wall High Pass Filter]
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* [https://www.dxengineering.com/parts/hiz-hpf Hi Z Antennas Hi Pass Filters]
 
* [http://www.iceradioproducts.com/filtersrf.html#bcb ICE BCB Filters]
 
* [http://www.iceradioproducts.com/filtersrf.html#bcb ICE BCB Filters]
* [https://www.kiwa-electronics.com/ Kiwa Electronics Filters page]
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* [https://kiwa-electronics.com/ Kiwa Electronics]
 
* [http://www.parelectronics.com/swl_filters.htm PAR BCST-HPF Filter]
 
* [http://www.parelectronics.com/swl_filters.htm PAR BCST-HPF Filter]
* [http://www.parelectronics.com/fm-broadcast.php PAR FM Broadcast filter]
 
 
* [http://www.scannermaster.com/SearchResults.asp?Cat=39 Scanner Master Filters page]
 
* [http://www.scannermaster.com/SearchResults.asp?Cat=39 Scanner Master Filters page]
* [http://www.stridsberg.com/prod02.htm Stridsberg Engineering Filters]
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* [http://www.stridsbergeng.com/filters.html Stridsberg Engineering Filters]
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* [http://www.scott-inc.com/html/notch.htm Tunable AM Band notch filter]
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* [http://www.hard-core-dx.com/nordicdx/antenna/special/highpass.html Homebrew High Pass Filter]
  
 +
  
 
==Preamplifiers==
 
==Preamplifiers==
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; Transmatches
 
; Transmatches
 
* [https://steadynet.com/emtech/ EMTech]
 
* [https://steadynet.com/emtech/ EMTech]
* [https://www.universal-radio.com/catalog/preamps/2964.html MFJ-956]  
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* [https://mfjenterprises.com/collections/tuners/products/mfj-16010?_pos=1&_sid=b95ad564c&_ss=r MFJ-16010]  
* [https://www.universal-radio.com/catalog/preamps/1329.html MFJ-16010]  
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* [https://mfjenterprises.com/collections/mfj-enterprises/products/mfj-9201?_pos=1&_sid=b68e43450&_ss=r MFJ-9201 QRP Antenna Tuner]
 
   
 
   
  
 
; Passive Preselectors
 
; Passive Preselectors
* [http://www.mfjenterprises.com/Product.php?productid=MFJ-1046  MFJ-1046]
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* [https://www.hamradiosecrets.com/hf-preselector.html A Simple Low Cost HF Preselector] via Ham Radio Secrets
 
* [http://www.crosscountrywireless.net/preselector.htm Cross Country HF Preselector]
 
* [http://www.crosscountrywireless.net/preselector.htm Cross Country HF Preselector]
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* [https://shop.elad-usa.com/preselector/ Elad Preselectors and parts]
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* [http://herostechnology.co.uk/pages/hf_preselector.html Heros Technology HF Preselector SCR CAT 2020]
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* [http://herostechnology.co.uk/pages/Tiny_CAT_SCR_Radio_preselector.html Heros Technology Tiny CAT SCR Preselector]
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* [https://mfjenterprises.com/collections/tuners/products/mfj-956?_pos=1&_sid=037138021&_ss=r MFJ-956]
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* [https://mfjenterprises.com/collections/mfj-enterprises/products/mfj-1046?_pos=1&_sid=cd9f2ff98&_ss=r  MFJ-1046]
  
  
 
; Active Preselectors
 
; Active Preselectors
* [https://www.universal-radio.com/catalog/preamps/6146.html Apex Radio 530-AP]
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* [https://mfjenterprises.com/collections/tuners/products/mfj-959c?_pos=1&_sid=eb7b89bb3&_ss=r MFJ-959C]
* [http://www.mfjenterprises.com/Product.php?productid=MFJ-1040C MFJ-1040C]
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* [https://mfjenterprises.com/collections/mfj-enterprises/products/mfj-1020c?_pos=1&_sid=87513119d&_ss=r  MFJ-1020C]
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* [https://mfjenterprises.com/products/mfj-1040c?_pos=1&_sid=0d0e42441&_ss=r MFJ-1040C]
 
* [http://www.palstar.com/en/mw550p/ Palstar MW550P MW Active Preselector/tuner]
 
* [http://www.palstar.com/en/mw550p/ Palstar MW550P MW Active Preselector/tuner]
  
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* [https://www.universal-radio.com/catalog/preamps/pclp.html Ameco PCL-P]
 
* [https://www.universal-radio.com/catalog/preamps/pclp.html Ameco PCL-P]
 
* [https://www.universal-radio.com/catalog/preamps/pt.html Ameco PT]
 
* [https://www.universal-radio.com/catalog/preamps/pt.html Ameco PT]
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* [https://www.universal-radio.com/catalog/preamps/6146.html Apex Radio 530-AP]
 
* [https://www.universal-radio.com/catalog/preamps/DP40.html McKay Dymek DP-40 passive preselector]
 
* [https://www.universal-radio.com/catalog/preamps/DP40.html McKay Dymek DP-40 passive preselector]
 
* [https://www.universal-radio.com/catalog/preamps/DP4044.html McKay Dymek DP-4044 passive preselector]
 
* [https://www.universal-radio.com/catalog/preamps/DP4044.html McKay Dymek DP-4044 passive preselector]
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* [https://www.universal-radio.com/catalog/preamps/P410X.html Palomar P410X transceiver preamp]
 
* [https://www.universal-radio.com/catalog/preamps/P410X.html Palomar P410X transceiver preamp]
 
* [https://www.universal-radio.com/catalog/preamps/3790.html RF Systems P-3 passive preselector]
 
* [https://www.universal-radio.com/catalog/preamps/3790.html RF Systems P-3 passive preselector]
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** [http://www.naswa.net/journal/2000/01/equip200001 NASWA Journal Review of the RF Systems P-3] (with response curves)
  
  
 
; Tuners
 
; Tuners
 
* [https://www.universal-radio.com/catalog/preamps/1643.html MFJ 959B Antenna Tuner]
 
* [https://www.universal-radio.com/catalog/preamps/1643.html MFJ 959B Antenna Tuner]
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---
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* Return to [[Decoding the SW Radiogram Broadcasts]]
  
 
[[Category:HF Antennas]]
 
[[Category:HF Antennas]]
 
[[Category:Amateur Radio Antennas]]
 
[[Category:Amateur Radio Antennas]]
 
[[Category:Receive-Only Antennas]]
 
[[Category:Receive-Only Antennas]]

Latest revision as of 21:17, 10 March 2021

Antennas

  • No matter how good the radio, without an antenna, it won't hear very much. Here are 2 places with lots of links and information on the subject
    • HF Antennas
    • Loops Some are broadbanded enough to reach the HF spectrum
    • See Bobs America website for more technical discussions on preconditioners, tuners, reviews and more


Antenna Tuners

This term is widely misused in both the ham and listening communities. True antenna tuners are placed at the antenna feedpoint, not at the shack position. They are intended to insure that the antenna delivers as much energy as is possible from the antenna and down the feedline. They usually need a bit of RF to begin the tuning process, so for a listener, they're pretty much useless.


So-called 'antenna tuners', such as those marketed by MFJ, are more correctly called a transmatch. For a ham, a transmatch can be used to overcome difficulties with matching a transceiver to an antenna. This can happen for many reasons, but one that's common is to make an antenna work on a band that isn't matching very well, even though it's supposed to. Doing this without tuning can cause the RF finals to overheat, causing them to cut power, or in extreme cases, be damaged. Another use, depending on the design, is to limit any spurious emissions coming from the transceiver.


For a listener, a transmatch matches the impedance of an antenna to the impedance expected by the receiver. This allows energy to be transferred from the antenna and feedline to the radio, increasing the receive efficiency of the antenna.


Do I need to buy a transmatch that can handle high power?

In a word, no. Units like these are intended for hams running 1 kw of power, or some commercial applications. Many tuners that are designed for QRP (low power) amateur applications will work just fine for listening applications - just don't try to put too much power into them by accident.


What can a transmatch load?

For many years, hams have used transmatches to load things you wouldn't normally consider as an antenna. Things like bed springs, gutters and metal fences have all been used. There's no reason to think that a listener couldn't do the same thing.


What kind of transmatches are there?

There are several different circuits for transmatches; a good Google search on these terms will yield many results. Construction can be thought of as being easy to somewhat complex, depending on the skill of the builder.

  • Pi network tuner
  • L Tuner
  • Tee section Tuner
  • Z Match Tuner

Here are a couple of homebrewed solutions


Filters

In urban areas, it's sometimes necessary to add some front end filtering to eliminate reception (or at least reduce it) of MW signals. These signals can cause multiple false signals (often heard as distorted spurs) to appear throughout parts, or all, of the HF spectrum. This is particularly true of the many wide banded Software Defined Radios (SDRs) on the market.


It's important to evaluate if a filter will solve your problem before you buy it. The better ones have a response curve that will show you how the filter attenuates at different frequencies. A practical example would be something like this; you have a FM broadcaster at 100.3 Mhz that overloads your radio. The unit you are looking at has a response curve that shows attenuation doesn't start until 101 Mhz. Therefore this filter would be largely ineffective in blocking the 100.3 broadcaster. See the filters from PAR electronics and ICE for examples of a response curve diagram.



Preamplifiers

You will see many ads for broad banded and distribution preamps from various distributors, and in places like eBay. Some receivers even have a preamp built in. But just what is a preamp? A preamp is an untuned device that amplifies a wide range of frequencies, usually with no gain control.


This fact can cause considerable headaches, particularly for those living in urban areas with a lot of MW, FM and TV stations in the neighborhood. If your receiver (or SDR) can't handle the additional gain, not only do you risk hearing these stations where they don't belong, the background noise will also increase.


Preamps have their place in certain weak signal work on VHF and UHF (such as Earth-Moon-Earth experiments), but on HF, there is a better alternative...


Preselector

A preselector can come in two basic flavors...

  1. Passive- By far, these have the best application, particularly in use with an old time single conversion receiver, and SDRs that often lack robust front ends to reject spurious signals. Passive preselectors have no amplifier, but the tuning is so sharp that they severely attenuate signals from outside the frequency being tuned.
  2. Active- These units actually have an amplifier with a tuned circuit, and better ones like the Palomar, have a gain control so you can control the amount of gain you apply to the radio


Active preselectors are great for the older desktop radios whose sensitivity tends to drop off around 20 Mhz or so. It does take some practice to use, however. It's a mistake to run an active preselector at 100% gain all the time, because you could still overload the radio, and also increase the noise factor. Listen to the band you're tuning - lower frequencies tend to be noisier. You should consider running it at a very low gain setting, then slowly increase it. In some cases, at some point the automatic gain control in the radio will clamp down on the signal, so no matter how much more you amplify it, you may find it's not getting any stronger. Remember, you are tuning to increase the intelligibility, not increase the noise.


Another way an active preselector could be used is to use it to load a very short dipole - say not more than 1 meter (roughly 3 foot) for each leg. A number of years ago, a company called Datong marketed such an antenna (with a preamp right at the antenna feedpoint) that was popular in Europe and to some lesser extent in the Americas because it's easy to hide the antenna.


Passive preselectors are quite different. You tune a passive preselector until the signal is free from distortion and noise. By definition, you might see a small amount of gain, but nothing like what you would get from an active preselector. These units should be used on SDRs that lack a good front end to resist overloading when a lot of MW, FM or TV signals are in the area. Examples would include many of the SDRPlay units, the RTL-SDRs (with upconverters for HF coverage) and the Funcube. They will work just fine for old desktop communications receivers, too - but without the issues with having too much gain


Commercial Units

Please put any additional items here

Transmatches


Passive Preselectors


Active Preselectors


  • Note: These units were found on Universal's discontinued page. Use them for reference.
Preselectors/preamps


Tuners


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